Planets lacking plate tectonics and sufficient carbon dioxide and oxygen could make advanced civilizations like ours extremely rare, Manuel Scherf and Helmut Lammer of the Austrian Academy of Sciences suggested during a presentation at the Europlanet Science Congress and the Division for Planetary Science (EPSC-DPS) in Helsinki earlier this month.

According to their research, for a biosphere to persist long enough to allow for the evolution of complex life and subsequent advanced technology, an Earth-like planet needs to meet certain criteria.

First, there must be enough carbon dioxide to sustain photosynthesis and prevent atmospheric escape — but not too much that the atmosphere becomes toxic or traps too much heat. The key to this balance is plate tectonics, which regulate the amount of atmospheric carbon dioxide via the carbon-silicate cycle.

But plate tectonics won't maintain the biosphere forever. "At some point, enough carbon dioxide will be drawn from the atmosphere so that photosynthesis will stop working. For the Earth, that's expected to happen in about 200 million to roughly one billion years," Scherf said in a statement. Thus, a planet would also need a life-sustaining biosphere that lasts longer than the time it takes for technologically intelligent life to evolve. On Earth, that evolution took 4.5 billion years.

Second, a world must have a nitrogen-oxygen dominant atmosphere to develop an advanced civilization. Oxygen, in particular, is crucial not only for biology but also for technological advancement. For example, levels below about 18% oxygen could prevent the use of fire, which historically has been essential for metalworking and thus the development of advanced tools.

The team created models to compare the lifespans of biospheres with various atmospheric compositions to the amount of time it might take advanced civilizations to evolve. They concluded that if an advanced technological civilization were to exist in our Milky Way galaxy, the closest it would be to Earth is likely about 33,000 light-years away. Such a civilization would also have to survive for at least 280,000 years — and possibly much longer — for there to be any chance it overlaps with ours in time.

In other words, the odds are very slim that we coexist with another intelligent civilization in the Milky Way.

Despite the grim outlook, the authors encourage continued efforts, especially through SETI (the search for extraterrestrial intelligence). "Although ETIs [extraterrestrial intelligences] might be rare, there is only one way to really find out, and that is by searching for it," said Scherf. "If these searches find nothing, it makes our theory more likely, and if SETI does find something, then it will be one of the biggest scientific breakthroughs ever achieved, as we would know that we are not alone in the universe."

A team from NASA's Jet Propulsion Laboratory (JPL) and Penn State University looked at when and where human transmissions would be most detectable by intelligent life outside the solar system. This helped to build patterns that could be employed by SETI in its hunt for signs of intelligent life or "technosignatures" beyond the solar system.

"Humans are predominantly communicating with the spacecraft and probes we have sent to study other planets like Mars," team leader and Penn State Eberly College of Science researcher said in a statement. "But a planet like Mars does not block the entire transmission, so a distant spacecraft or planet positioned along the path of these interplanetary communications could potentially detect the spillover; that would occur when Earth and another solar system planet align from their perspective. This suggests that we should look for alignment of planets outside of our solar system when searching for extraterrestrial communications."

To reach their conclusion, Fan and colleagues looked at data logs from NASA's Deep Space Network (DSN), a relay system that enables two-way communication with spacecraft and planetary rovers. The team focused on transmissions to deep space instruments like interplanetary spacecraft and space-based telescopes rather than transmissions to equipment in orbit around Earth, like satellites and low-Earth orbit spacecraft. This is because the latter type of signal is low-power and unlikely to be detected at vast distances.

The researchers chose the DSN from a range of alternative deep-space networks because this NASA-operated relay has led more space missions than any other to date. That makes it the ideal representation of communications between Earth and deep space.

"NASA's Deep Space Network provides the crucial link between Earth and its interplanetary missions like the New Horizons spacecraft, which is now outbound from the solar system, and the James Webb Space Telescope (JWST)," team member and JPL scientist Joseph Lazio said. "It sends some of humanity's strongest and most persistent radio signals into space, and the public logs of its transmissions allowed our team to establish the temporal and spatial patterns of those transmissions for the past 20 years."

By comparing DSN logs with spacecraft locations, the team was able to determine the direction of human transmissions to this equipment and the timing of such communications. They found that deep-space radio signals were predominantly directed toward spacecraft near Mars, with common transmissions directed toward the other planets of the solar system.

There were also a great deal of transmissions toward the gravitationally stable points between Earth and the sun known as Lagrange points. That is because these are the ideal locations around our planet for space telescopes like the JWST.

"Based on data from the last 20 years, we found that if an extraterrestrial intelligence were in a location that could observe the alignment of Earth and Mars, there's a 77% chance that they would be in the path of one of our transmissions — orders of magnitude more likely than being in a random position at a random time," Fan said. "If they could view an alignment with another solar-system planet, there is a 12% chance they would be in the path of our transmissions.

"When not observing a planet alignment, however, these chances are minuscule."

Alien signals could be found where the planets allign

These findings give astronomers a hint at where and when to look for technosignatures; the periods during which extrasolar planets, or "exoplanets," in other star systems align with their stars are of particular interest.

Alignments between exoplanets and stars, called transits, that occur when these worlds cross the face of their parent star from our perspective on Earth, are particularly useful for detecting planets beyond the solar system.

"However, because we are only starting to detect a lot of exoplanets in the last decade or two, we do not know many systems with two or more transiting exoplanets," Fan said. "With the upcoming launch of NASA's Nancy Grace Roman Space Telescope, we expect to detect a hundred thousand previously undetected exoplanets, so our potential search area should increase greatly."

The team found that because the planets are mostly on the same orbital plane, signals passing through the DNS tend to be oriented within around 5 degrees of Earth's orbital plane rather than travelling out at an extreme angle. They also found that the average signal passing through this NASA relay could be detectable at a distance of up to 23 light-years away, assuming extraterrestrial life with telescope technology similar to ours.

In combination, these factors indicate that the search for technosignatures should focus on planetary systems that are edge-to-edge with the solar system in terms of orientation (think two plates sat on a flat surface), and are no more than 23 light-years away.

The next step for the team is to begin identifying planetary systems that fit these criteria.

While the team's research predominantly focuses on radio transmissions, the model could also apply to laser transmissions like the laser communication system currently being tested by NASA. Laser transmissions are, however, less likely to "leak" past their intended targets than radio signals.

"Humans are pretty early in our spacefaring journey, and as we reach further into our solar system, our transmissions to other planets will only increase," team member Jason Wright, director of the Penn State Extraterrestrial Intelligence Center, said. "Using our own deep space communications as a baseline, we quantified how future searchers for extraterrestrial intelligence could be improved by focusing on systems with particular orientations and planet alignments."

The team's research was published on Thursday (Aug. 21) in The Astrophysical Journal Letters.

Recently, the Coller Dolittle Challenge awarded the winner of its first $100,000 annual prize to accelerate progress toward interspecies two-way communication. A prize of equal value will be awarded every year until a team deciphers the secret to interspecies communication.

This year's winning team of researchers has discovered that dolphin whistles could function like words — with mutually understood, context-specific meaning.

Crack the code

The winning team was led by Laela Sayigh from the Woods Hole Oceanographic Institution. The researchers are studying the resident bottlenose dolphin community offshore of Sarasota, Florida.

They were on the lookout for "non-signature" whistles, which comprise approximately 50% of the whistles produced by Sarasota dolphins. Non-signature whistles differ from the more widely studied "signature" whistles, which are referential, name-like vocalizations.

Sayigh's team used non-invasive suction-cup hydrophones, which they placed on the dolphins during unique catch-and-release health assessments, as well as digital acoustic tags.

"Bottlenose dolphins have long fascinated animal communication researchers," Sayigh said in a statement. "Our work shows that these whistles could potentially function like words, shared by multiple dolphins."

Sayigh and her team can now use deep learning in an attempt to "crack the code" and analyze those whistles.

Zoologist's guide to the galaxy

But what does all this have to do with E.T.?

"My interests are very firmly here on Earth, in learning about how dolphins communicate with each other," Sayigh told Space.com "I do know that there are others in the animal communication world that are interested in this, however."

One of those researchers is Arik Kershenbaum, an associate professor and director of studies at Girton College, part of the University of Cambridge in England. He's the author of "The Zoologist's Guide to the Galaxy: What Animals on Earth Reveal About Aliens — and Ourselves" (Viking, 2020).

Kershenbaum explained that the book is about life on Earth, because "that's all we have to look at." He also contributed a white paper for a workshop at the Search for Extraterrestrial Intelligence (SETI) Institute in California, titled "What Animal Studies Can Tell Us about Detecting Intelligent Messages from Outside Earth."

Cross-species database

In that paper for the SETI Institute, Kershenbaum and colleagues concluded that animal communication research is the closest we are likely to get to studying extraterrestrial signals, until such signals are actually received.

"Many of the challenges facing SETI research are similar to those already addressed in the investigation of animal behavior, and the evolutionary origins of human language," they wrote. "Indeed, the evolution of language on Earth may in fact have been driven and constrained by similar principles to those operating on life on other planets."

The researchers have proposed the establishment of a large cross-species database of communicative signals, made available to all SETI and animal behavior researchers.

In addition, they also proposed that tools, algorithms and software used to analyze these signals should be made publicly available for application to these data sets, "so that comparative studies can take full advantage of the expertise from the biological, mathematical, linguistic and astronomical communities."

Complex vocalizations

The topic of dolphin language interpretation, as well as the vocalizations of humpback whales and the field of non-human communications more broadly, is increasingly drawing the interest of SETI researchers and astrobiologists, explained Bill Diamond, president of the SETI Institute.

Humpback whales have very complex vocalizations, Diamond told Space.com, "where it seems clear that they are transmitting information and not simply making sounds associated with mating, feeding or dealing with threats. They plan ahead and communicate complex instructions to one another."

Leading that look is SETI researcher Laurance Doyle, who's working on a project in partnership with the Alaska Whale Foundation to study the vocalizations of humpback whales.

Fundamental rules

For Diamond, the relevant research question is whether or not there are some fundamental mathematical rules associated with the transmission of information that would be universal — like the laws of physics and chemistry — within our known universe.

"If there's an underlying rule structure to the transmission of information, and we can decipher it," Diamond said, "we would firstly be able to recognize a detected SETI signal as containing information, and therefore intelligence. And, possibly, we might even ultimately be able to translate it!"

According to Diamond, "there's definitely a connection between SETI/astrobiology and the study of non-human communication and non-human intelligence."

To do this, they built a network of all-sky cameras across the globe, which they named the Global Fireball Observatory.

"This has been a decade-long detective story, with each recorded meteorite fall providing a new clue," one of the project’s founders, Peter Jenniskens of the SETI Institute and NASA Ames Research Center, said in a statement. "We now have the first outlines of a geologic map of the asteroid belt."

Jennisken’s colleague, Hadrien Devillepoix of Curtin University, added: "Others built similar networks spread around the globe, which together form the Global Fireball Observatory. Over the years, we have tracked the path of 17 recovered meteorite falls."

The team's research was published on Monday (March 17) in the journal Meteoritics & Planetary Science.

From the main asteroid belt to Earth's atmosphere

Meteorites are rocks from space that survive their fiery descent through Earth's atmosphere and reach the ground. More than just dazzling streaks of light as meteors, these ancient fragments are among the oldest materials in our solar system, originating from planets, asteroids, and comets.

Most meteorites, however, originate from the solar system's main asteroid belt—a vast region between the orbits of Mars and Jupiter where more than a million asteroids circle the sun. Its formation remains a subject of debate, but astronomers believe it dates back around 4.5 billion years to the formation of the solar system's planets. These asteroids are thought to consist of leftover planetesimals, the building blocks of planets that never fully coalesced into a larger body.

The asteroid belt contains debris fields known as clusters, which form when larger asteroids break apart due to random collisions. These smaller fragments remain grouped together and are called asteroid families.

By measuring the radioactive elements present in a meteorite, astronomers can determine their age and match it to the "dynamical age" of asteroid debris fields. The dynamical age is the amount of time that has passed since an asteroid or group of asteroids was disrupted or scattered, determined by studying how the objects have spread out over time due to their movements and interactions, like gravitational forces or collisions.

The more spread out the asteroids are, the older the debris field is likely to be. Essentially, it gives an estimate of how long it has been since the original disruption that caused the objects to scatter.

By analyzing data gathered from watching the night sky and by using a combination of video footage and photographic observations of meteors, Devillepoix, Jenniskens, and their teams have tracked the origins of 75 meteorites in the asteroid belt.

"Six years ago, there were just hints that different meteorite types arrived on different orbits, but now, the number of orbits (N) is high enough for distinct patterns to emerge," they wrote in their paper.

One particularly interesting finding centers around iron-rich ordinary chondrite meteorites or "H chondrites," one of the most common types of meteorites that land on Earth. Their chemistry is considered primitive because they have never undergone melting and have experienced very few chemical interactions since their formation—making them valuable time capsules for understanding the early solar system.

"We now see that 12 of the iron-rich ordinary chondrite meteorites (H chondrites) originated from a debris field called 'Koronis,' which is located low in the pristine main belt," said Jenniskens. "These meteorites arrived from low-inclined orbits with orbital periods consistent with this debris field.

"By measuring the cosmic ray exposure age of meteorites, we can determine that three of these twelve meteorites originated from the Karin cluster in Koronis, which has a dynamical age of 5.8 million years, and two came from the Koronis2 cluster, with a dynamical age of 10-15 million years," he continued. “One other meteorite may well measure the age of the Koronis3 cluster: about 83 million years.”

The team also discovered that several groups of meteorites, including H-chondrites, originated from different regions in the asteroid belt. Some H-chondrites, with an age of about 6 million years, come from the Nele asteroid family, while others, with an exposure age of 35 million years, come from the inner main belt, likely from the Massalia asteroid family.

They also found that the second most common group of meteorites, stony L chondrites, and the least abundant stony meteorites, LL chondrites, which are primarily from the inner main belt, trace back to the Flora and Hertha asteroid families. The L chondrites, in particular, experienced a violent origin 468 million years ago and are linked to a massive collision.

While this provides one of the most comprehensive maps of the asteroid belt to date, not all meteorites in the database were assigned, and some assignments still carried uncertainty.

But for Devillepoix and Jenniskens, this is just the beginning.

"We are proud about how far we have come, but there is a long way to go," said Jenniskens. "Like the first cartographers who traced the outline of Australia, our map reveals a continent of discoveries still ahead when more meteorite falls are recorded.

"We're arguing that intelligent life may not require a series of lucky breaks to exist," said lead author Dan Mills of the University of Munich in a statement. "Humans didn't evolve 'early' or 'late' in Earth's history, but 'on time' when the conditions were in place."

It was the Australian physicist Brandon Carter who first popularized the notion that life on Earth was the result of a sequence of unlikely events, which he described as "hard steps" in a 1983 paper.

A black hole theorist, from time to time Carter also dipped his hand into more existential matters, specializing in drawing assumptions from probabilistic and anthropic (i.e. the argument that conclusions about the nature of the cosmos have to be constrained by the fact that we exist) reasoning to say something about our existence in the universe.

Related: The search for alien life

This is no better seen than in his Doomsday argument, in which Carter posits that we, as individuals, are more likely to exist at a time when the greatest number of humans are alive. For example, imagine every human who ever lived is given a number based on the order in which they were born, and then these numbers are pulled from a pot like the numbers in a lottery — you're more likely to pull a higher number than a very low number if the total number of humans who have lived and will ever live is large. Since population growth can be modeled as exponential, the fact that we exist now with a relatively low birth number compared to all the hundreds of billions to trillions of people who will follow us suggests that something catastrophic could be about to happen to the human race that will curtail future population numbers. At least, that's the argument; philosophers and statisticians have been arguing about it ever since Carter proposed it.

Carter's "hard steps" model of our evolution on Earth is similarly probabilistic in nature. The sun is nearing the halfway point of its approximately 10-billion-year lifespan, and yet it's taken us — Homo sapiens — nearly all of that time to arrive on the scene. Carter could not see any reason why it would take so long for human-like life to evolve on Earth if complex life is common in the universe. This suggested to Carter that the development of human-like life must be difficult, passing through a series of evolutionary bottlenecks for which the chances of life succeeding are so remote that we would not typically expect those evolutionary transitions to occur in the lifetime of Earth. Life on our planet would therefore be a complete fluke, unlikely to be repeated elsewhere in the universe.

The hard steps idea has subsequently morphed into the concept of the "great filter," the idea that something in the history of all life inevitably brings that life to an end. Suggested great filters have included the origin of life in the first place, the evolution of technological life and the ability of said life to wipe itself out. The existence of the great filter would certainly help explain the apparent "great silence" in the universe that SETI (search for extraterrestrial intelligence) researchers have encountered, with no confirmed evidence of alien life in all the decades that we have been searching.

However, like the Doomsday argument, the "hard steps" model has its critics, and now adding to them are the authors of a new paper that highlights what they say is a fallacy in Carter's reasoning.

Carter specifically assumed that the age of the sun, and therefore the Earth, should have no bearing on how quickly complex life evolved. However, the new paper by Mills (a geomicrobiologist), along with Penn State University co-authors Jennifer Macalady (a professor of geosciences), Adam Frank and Jason Wright (both astrophysicists), points out that the age of the sun and therefore the Earth very much have something to do with it.

The team selected five of the more universally agreed-upon "hard steps:" the origin of life, the evolution of eukaryotes (organisms with cells made from a nucleus containing genetic information surrounded by a membrane), the oxygenation of Earth's atmosphere, the development of complex multicellular life and the arrival of Homo sapiens. They then looked at how geological and atmospheric changes to Earth might have affected when these supposedly hard steps occurred. If Earth were initially hostile to these supposed hard steps, it would naturally explain why they took so long to pass — because they had to wait for Earth to reach the point where they could be possible.

Take, for example, the oxygenation of Earth's atmosphere. For over two billion years after its formation, Earth's atmosphere was mostly carbon dioxide. It was only about 2.1 to 2.4 billion years ago that Earth's atmosphere began to fill with oxygen. This was thanks to the onset of photosynthesis, brought about by the evolution of microbes called cyanobacteria. In turn, the development of cyanobacteria relied on certain climactic and environmental conditions. In some models, the oceans of this era were hot, and the water would have had to cool below 70 degrees Celsius (158 degrees Fahrenheit) for cyanobacteria to evolve. In other models, conditions were milder and the development of cyanobacteria then depended upon the availability of freshwater and how much of Earth's landmass was above sea level. Either way, cyanobacteria's evolution and the onset of photosynthesis and the oxygenation of the atmosphere was delayed until these conditions were met; it couldn't have happened any sooner.

And even once cyanobacteria were ingesting carbon dioxide and exhaling oxygen via photosynthesis, it took time for oxygen levels to build up. Multicellular life requires a certain abundance of oxygen, with more complex life in general requiring more oxygen. The oxygen abundance in the atmosphere suitable for the evolution of Homo sapiens didn't occur until 400 million years ago — meaning that for 91% of Earth's history, there wasn't enough oxygen in the atmosphere to support human life.

In other words, Mills' team propose that these were not "hard steps" as Carter saw them, but that life simply had to wait until Earth could facilitate them — that Earth and life had to co-evolve together.

Related: Fermi Paradox: Where are the aliens?

Other variables that may have had an effect on how soon the different stages of life's evolution could occur include atmospheric ozone levels, nutrient availability, decreasing sea surface temperatures, decreasing ocean salinity, snowball Earth periods in which the planet completely iced over, and the development of plate tectonics.

"This is a significant shift in how we think about the history of life," said Macalady. "It suggests that the evolution of complex life may be less about luck and more about the interplay between life and its environment, opening up exciting new avenues of research in our quest to understand our origins and our place in the universe."

We know from geological evidence that life existed on Earth as early as 3.7 billion years ago, and possibly even earlier. The initial development of life on Earth is known as the "habitability boundary." As different windows of habitability subsequently opened up, life would have been able to evolve in bursts. And if this is the way it happens on Earth, it could be the way it happens on other worlds, too — and perhaps faster or more slowly, depending upon how the geology of those worlds develops.

There is a caveat, in that evolutionary biologists still do not understand how life originated on Earth. This moment of genesis is currently lost in the mists of time, and we cannot yet say whether it was a fluke one-off event or whether it was an easy step. One possibility is that life developed on multiple occasions on Earth, but all the other lineages went extinct, leaving only ourselves — the descendants of LUCA, the last universal common ancestor, from which all known life on Earth evolved — as the only ones left standing. This would give the illusion that life originated only once when it could have had several independent origins.

Other mysteries include how biological cells first evolved, and what caused the dramatic onset of complex life during the Cambrian explosion 540 million years ago.

It is still entirely possible that these were unique and rare events, but the new paper is not arguing that life is common in the universe, only that the concept of hard steps in evolution is not necessarily true and that the development of planetary environments has a big role to play, counter to Carter's original model.

Another caveat is that, so far, astronomers have not yet found another world like Earth, so geologists cannot yet say whether the way in which Earth's geology and atmosphere developed is typical or not. It could yet be that creating a habitable world is where the hard steps really lie.

Until we discover true extraterrestrial life, whether that be microbes on Mars or bonafide little green men, we will continue to grapple with the possibility that Earth and its life are unique. For now, it's a lonely universe out there.

The Mills et al paper was published on Feb. 14 in the journal Science Advances.

It seems like a somewhat reasonable assumption that if other civilizations are out there in the universe, eventually they will discover how to emit powerful radio broadcasts. Radio waves are capable of traversing great interstellar distances, so they make a great calling card. This is the foundational assumption for the search for extraterrestrial intelligence (SETI). Strange radio signals might be a sign of an artificial transmission from an alien species.

But our Milky Way galaxy is swimming in radio emissions of all sorts, from exploding stars to the vibrational hum of the galaxy's magnetic field. Plus, humanity has developed a particular fondness for radio transmissions, so any radio search for aliens must deal with enormous quantities of human-caused signals.

Previous SETI searches have scanned large areas of the sky and flagged anything interesting that popped up. Then, researchers have combed through the flagged results by hand, searching for signs of artificial transmission while ruling out potential causes of human-made interference.

Previous SETI searches have also come up totally empty — which isn't a big surprise, since this semimanual technique limits how much data any one research team can process.

Enter COSMIC, the Commensal Open-source Multi-mode Interferometric Cluster. COSMIC is a computer and software system that piggybacks on that of the Karl G. Jansky Very Large Array, the iconic radio array located in the desert of New Mexico.

COSMIC is designed to automate the process of SETI searches as much as possible. By combining fast processing and a series of restrictive filters, the system searches signal after signal, deciding if it's likely to be artificial and, if it is, determining if it matches the signature of a known terrestrial source.

In particular, COSMIC searches for radio signals that are very tightly focused, suggesting that they come from a very small source, like a planetary surface. Next, it looks for Doppler shifting of that radio signal. If the signal comes from a planet, the motion of the planet will either redshift or blueshift the signal, depending on whether the planet is moving away from or toward us when the signal was emitted. If the system finds a signal matching these properties, it is flagged and advanced to the next stage of filtering.

Related: How AI is helping us search the universe for alien technosignatures

Next, the astronomers behind COSMIC know the properties of terrestrial radio emission. This unwanted artificial emission follows particular statistical properties. If the flagged signal of interest matches those properties, the signal is rejected. Any remaining signals are then flagged for further review.

The COSMIC system is a part of the VLA Sky Survey, which completed a scan of roughly 82% of the Northern Hemisphere's sky. All told, the COSMIC system analyzed over 950,000 individual pointings of the telescope. Although the system initially flagged thousands of potentially interesting signals, none survived all of the filtering steps.

In other words, a deep radio search of a good chunk of the Northern Hemisphere found no artificial radio signals.

Although this is initially discouraging, this result still represents an important advance in our search for alien life. We can use this data to narrow down the probabilities of life appearing on any one planet, and we now have a valuable tool for collecting and processing data in future surveys, which might turn up something much more interesting.

In particular, the team led by Sofia Sheikh from the SETI Institute was interested in how the signals from pulsars distort as they travel through space. Pulsars are dense stellar remnants called neutron stars that blast out beams of radiation that sweep across the cosmos as they spin. To study how these stars' signals are distorted in space, the team turned to archival data from Arecibo, a 1,000-foot (305-meter) wide suspended radio dish that collapsed on Dec. 1, 2020, after the cables supporting it snapped, punching holes in the dish.

The researchers investigated 23 pulsars, including 6 which had not been studied before. This data revealed patterns in pulsar signals showing how they were impacted by the passage through gas and dust that exists between stars, the so-called "interstellar medium."

When the cores of massive stars rapidly collapse to create neutron stars, they can create pulsars capable of spinning as fast as 700 times every second thanks to the conservation of angular momentum.

When pulsars were first discovered in 1967 by Jocelyn Bell Burnell, some proposed the frequent and highly regular periodic pulsing of these remnants to be signals from intelligent life everywhere in the cosmos. Just because we now know that isn't the case doesn't mean SETI has lost interest in pulsars!

The radio wave distortions the team was interested in are known as diffractive interstellar scintillation (DISS). DISS is somewhat analogous to the patterns of rippling shadows seen at the bottom of a pool as light passes through the water above.

Instead of ripples in water, DISS is caused by charged particles in the interstellar medium that create distortions in radio wave signals traveling from pulsars to radio telescopes on Earth.

The team's investigation revealed that the bandwidths of pulsar signals were wider than current models of the universe suggest should be the case. This further implied that current models of the interstellar medium may need to be revised.

The researchers found that when galactic structures such as the spiral arms of the Milky Way were accounted for, the DISS data was better explained. This suggests that challenges in modeling the structure of our galaxy should be faced in order to continually update galactic structure models.

Understanding how signals from pulsars work is important to scientists because, when considered in large arrays, the ultraprecise periodic signals from pulsars can be used as a timing mechanism.

Astronomers use these "pulsar timing arrays" to measure the tiny distortions in space and time caused by the passage of gravitational waves. A recent example is the use of the NANOGrav pulsar array to detect the faint signal from the gravitational wave background.

This background hum of gravitational waves is believed to be the result of supermassive black hole binaries and mergers in the very early universe. A better understanding of DISS could help refine the detection of gravitational waves by projects like NANOGrav.

"This work demonstrates the value of large, archived datasets," Sheikh said in a statement. "Even years after the Arecibo Observatory's collapse, its data continues to unlock critical information that can advance our understanding of the galaxy and enhance our ability to study phenomena like gravitational waves."

The team's research was published on Nov. 26 in The Astrophysical Journal.

UFOs came to Washington again today.

The U.S. House of Representatives' Committee on Oversight and Accountability held a hearing titled "Unidentified Anomalous Phenomena: Exposing the Truth" at the Rayburn House Office Building in Washington, D.C. at 11:30 a.m. EST (1530 GMT) on Wednesday (Nov. 13). Unidentified anomalous phenomena (UAP) is a relatively new catch-all term that includes sightings of unexplained objects or events that take place in the air, underwater, in space, or that travel between those domains. 

Like previous congressional UFO hearings, today's event featured testimony from current U.S. military personnel who claim the American government has for decades hidden evidence of advanced technologies and otherworldly visitors from the public. A multitude of anecdotes were presented about flying orbs coming out of the ocean, disc-shaped objects, and craft "exhibiting flight and structural characteristics unlike anything in our arsenal." While such claims are nothing new, what is noteworthy about today's hearing are the pedigrees of some of the whistleblowers who testified, including a former U.S. counterintelligence officer, a retired U.S. Navy rear admiral and a former NASA associate administrator. All of them stressed the need for more government transparency, less stigma about the UFO topic and new policies to bring UAP data out of the "black" classified world and into the public domain.  

This isn't the U.S. government's first attempt to investigate the recent wave of UFO claims that began in 2017. A similar hearing was held last year, in which a whistleblower told Congress the U.S. government is hiding evidence of 'non-human intelligence.' 

The Pentagon also created the All-Doman Anomaly Resolution Office (AARO) in 2022 to investigate UAP reports and government data about UFOs, but critics, including some government officials, are skeptical of the office's aims and methods. 

Related: UFO whistleblower tells Congress the US government is hiding evidence of 'non-human intelligence'

"AARO is unable, or perhaps unwilling, to bring forward the truth about the government's activities concerning UAPs," Representative Nancy Mace (R-South Carolina) said during the hearing's opening remarks today. "I'm disturbed that AARO itself lacks transparency; even its budget is kept from the public. So if there is no 'there' there, then why are we spending money on it? And by how much? Why the secrecy?"

Other representatives stressed the need for transparency and data analysis today, a common theme of other recent UAP studies. "We have evidence that what we are detecting things, and we know that we don't understand them, and this is worth investigating," Rep. Robert Garcia (D-CA) said. "I believe we can always be more transparent. To me, this hearing and others are simply about the truth and getting to the facts of what these UAPs actually are."

Luis Elizondo, a former U.S. counterintelligence officer who has been vocal about such claims in recent years, told the assembled representatives at the hearing that "excessive secrecy has led to grave misdeeds against loyal civil servants, military personnel and the public — all to hide the fact that we are not alone in the cosmos." 

We are "in the midst of a multi-decade, secretive arms race  — one funded by misallocated taxpayer dollars and hidden from our elected representatives and oversight bodies," Elizondo stated during his testimony. 

Elizondo, who claims to have previously investigated UFOs as part of a secret Pentagon program, suggested that the U.S. government create a "whole-of-government" approach to studying UAP, create a national UAP strategy and offer protections so that whistleblowers who are "desperate to do the right thing can come forward without fear."

During questioning, Elizondo was asked if some of the "advanced technologies" that have been seen monitoring sensitive military installations around the globe could be operated by aliens or private companies. "Maybe both," Elizondo replied.

Elizondo also stated point-blank to Rep. Mace's questioning that the U.S. government has programs to retrieve crashed UAP and reverse-engineer them, but avoided giving any specifics in an unclassified public setting such as the hearing.

Rep. Jared Moskowitz (D-FL) then questioned Elizondo, asking the former counterintelligence agent about a document he signed that limits him from speaking publicly about crash retrieval programs. "The document said you can't talk about crash retrieval. Well, you know, you can't talk about Fight Club if there's no Fight Club, correct?"

Like other witnesses, Elizondo stated that the alleged excessive government secrecy around UFOs harms national security. In response to questioning from Rep. Tim Burchett (R-TN), Elizondo stated that, if UAP sightings turned out to be technologies operated by adversarial nations, it would be "an intelligence failure eclipsing 9/11 in order of magnitude."

Retired U.S. Navy rear admiral Tim Gallaudet offered similar testimony as Elizondo. "We know from last year's UAP hearing and recent statements and publications by credible whistleblowers that UAP, NHI [non-human intelligence], and their technology of unknown origin (TUO) represent a new realization that we are not the only advanced intelligence in the universe," Gallaudet said on Wednesday, according to his published remarks. 

"Unelected officials in the U.S. government do not have an exclusive right to this knowledge about the nature of reality. The American people have a right to that knowledge," Gallaudet said. The retired rear admiral also stressed the national security and airspace safety concerns related with UAP sightings, calling them "extensive."

When Rep. Garcia asked Gallaudet and other witnesses what UAP might represent, the retired rear admiral said he believes they are evidence of a "non-human higher intelligence."

Former NASA Associate Administrator for Space Policy and Partnerships Michael Gold also testified at today's hearing, and previously served on NASA's UAP study team. Gold's testimony was more grounded; for example, he stressed the need for NASA to contribute its authority and expertise toward analyzing what UAP data it might already possess and helping dispel the stigma associated with the UFO topic. 

"Our best tool for unlocking the mystery of UAP is science, but we cannot conduct a proper inquiry if the stigma is so overwhelming that just daring to be part of a NASA search team elicits such a vitriolic response," Gold said during today's hearing. "Therefore, one of the most important actions that can be taken, relative to exposing the truth of UAP, is to combat the stigma, and this is where I believe that NASA can be eminently helpful."

Gold added that NASA has a massive archive of data that could possibly contain evidence of UAP, and suggested that artificial intelligence/machine learning algorithms could help sort through the agency's trove of data to help shine light on the UFO phenomenon. In addition, the former NASA associate administrator said the agency should develop specialized instruments that might be able to gather useful data about UAP.

Related: NASA UFO report finds no evidence of 'extraterrestrial origin' for UAP sightings

Journalist Michael Shellenberger also testified today, telling the representatives that there's a "growing body of evidence that the government is not being transparent about what it knows about unidentified anomalous phenomena (UAP), formerly called UFOs, and that elements within the military and IC [intelligence community] are in violation of their Constitutional duty to notify Congress of their operations." 

Shellenberger stated that there is a secret program within the U.S. government known as "Immaculate Constellation" whose sole purpose is to collect UFO and UAP reports from military personnel and sensor data and quarantine them away from the rest of the government and military. While he noted that a Pentagon spokesperson has stated no such program exists, Shellenberger recounted prior examples in which the Department of Defense has initially denied knowledge of UAP-related information only to later change its stance and either admit the information exists or release it to the public. 

"The U.S. government appears to know significantly more about UAPs than it is revealing," Shellenberger said at the hearing. "But even those who believe the U.S. government has revealed all that it knows should have no objection to Congressional demands for greater transparency."

To conclude the meeting, Rep. Mace asked each of the witnesses to define what non-human biologics or non-human intelligence mean to each of them.

"I don't think it's a stretch, when you look at the diversity of life on this planet and the size of this universe, to think that there will be more diverse, higher-order, non-human intelligence throughout the universe, and that's probably what's visiting us," Gallaudet said.

Elizondo stated he would take a scientific approach: "The definition would be the ability to react to a stimulus in a manner that requires an intellectual thought process."

Gold, meanwhile, questioned whether non-human intelligence necessarily implies life, suggesting sophisticated artificial intelligence might be responsible for some UAP encounters. Shellenberger simply stated he did not know what they might be.

Related: The search for alien life

In today's hearing, as in other UFO hearings, there was a lot of telling and not a lot of showing. One of the core tenets of these whistleblower testimonies is that much of the credible UFO data is classified and can't be revealed to the public based on the military capabilities that some of that data could reveal. 

Whistleblowers have attested for years that, because advanced or classified sensors and satellites sometimes capture footage or photos of unexplained phenomena or advanced craft, those photos or videos are likewise classified by the U.S. government in order to not reveal America's full surveillance or sensing capabilities. 

Such was the case in 2023 when U.S. military aircraft shot down a mysterious object off the coast of Alaska. The American government has yet to release any imagery from the event, but a Canadian freedom of information request unveiled a photograph earlier this year of a balloon-like object.

Those incidents and others like it, such as a weeks-long drone incursion above Langley Air Force Base in Washington, D.C., were discussed in today's hearing. "The origin of these drones and their operators remains a mystery," Rep. Glenn Grothman (R-Wis.) said. "This incident and other sightings near sensitive military installations highlights the complexity of the UAP challenge facing our intelligence, defense and homeland security committees."

The European Space Agency's (ESA) ExoMars Trace Gas Orbiter Mars probe beamed the signal at us in May 2023 as part of "A Sign in Space," a multi-week art project led by Daniela de Paulis, the current Artist in Residence at the SETI Institute in Mountain View, California and the Green Bank Observatory in West Virginia. The project was intended as an experiment to test what types of techniques might be useful for decoding signals that might be detected as part of SETI (search for extraterrestrial intelligence) efforts.

After over a year, a father-daughter team has decoded that signal. Ken and Keli Chaffin were able to decipher the message after "following their intuition and running simulations for hours and days on end," according to an ESA statement. 

Before the simulated alien signal could be decoded, it first had to be extracted from the raw radio signal data. That took just 10 days, thanks to a group of some 5,000 citizen scientists. But that was the easy part.

Related: The search for alien life

It took the Chaffins over a year to decode the signal. They finally found that it "contained movement," ESA wrote in the statement, which suggested to them that it might harbor information about cellular formation or life. 

But decoding a signal doesn't necessarily mean that it can be understood. Now that the cryptic message has been decoded, citizen scientists like the Chaffins will have to begin attempting to interpret its contents and find possible meaning in it. 

And that's the overall goal of the A Sign in Space Project. "Receiving a message from an extraterrestrial civilization would be a profoundly transformational experience for all humankind," de Paulis said in a 2023 statement describing the project. 

"A Sign in Space offers the unprecedented opportunity to tangibly rehearse and prepare for this scenario through global collaboration, fostering an open-ended search for meaning across all cultures and disciplines."

But interpreting a message of true alien provenance could prove much, much harder, if it ever happens. Any simulated messages like the one beamed to Earth from the ExoMars Trace Gas Orbiter were created by humans and thus will embody how we view the universe and communicate our experience of it. 

All our ideas about language, data, information and communication are rooted in how physics work on Earth, how human sensory organs perceive the world around us, how human languages have evolved, etc. It's hard for us to imagine how these same processes might work on an exoplanet harboring life, simply because we've never found or experienced one yet.

For all we know, alien communication might more resemble a collection of odors or the movements of a pile of leaves in the wind than anything we recognize as language.

Still, the search has to begin somewhere. 

Projects like A Sign in Space offer useful thought experiments for planning how we might respond to the detection of a true alien radio signal. And the fact that this signal was decoded by citizen scientists shows exactly the type of out-of-the-box thinking that will likely be required when and if we ever receive that signal.

"More than astronomy, communicating with E.T. will require a breadth of knowledge," said Wael Farah, project scientist with the SETI Institute's Allen Telescope Array in northern California. "With A Sign in Space, we hope to make the initial steps towards bringing a community together to meet this challenge."

TRAPPIST-1 is a multi-planet system about 40.7 light-years away. Its seven rocky worlds, some of which lie in the habitable zone — the zone around a star where it isn't too hot nor too cold for a planet to host liquid water — are all bunched up so tightly that they transit their star every few days. The number of planets and their relative proximity to us make the TRAPPIST-1 system a tantalizing target for the search for extraterrestrial intelligence (SETI).

Although this latest search — in which the Allen Telescope Array of radio telescopes in California spent 28 hours in total listening to TRAPPIST-1 — did not detect any alien signals, "the point of the study was to demonstrate a more efficient search strategy, utilizing the natural orbital configuration of an edge-on multi-planet system to our advantage," Nicholas Tusay, a graduate student at Penn State University, told Space.com. 

Traditionally, SETI has scanned the sky in search of powerful signals directed at us. However, after decades of not finding anything, SETI researchers are increasingly considering other strategies. These include searching for radio leakage: incidental transmissions not intended for us, but which might leak out from a planetary system. Such transmissions could range from communications and spacecraft emissions to radar or even the equivalent of alien TV. However, because this incidental leakage would not be transmitted with the intention of being heard light-years away, it would likely be of much lower power than deliberate signals would be. 

The likelihood of us spotting such leakage by chance would thus be slim, so we need strategies that can improve the odds. 

To this end, Tusay led the observations of TRAPPIST-1, which took advantage of a phenomenon called planet–planet occultations (PPOs). An occultation occurs when one object in the sky appears to move in front of another. As the seven TRAPPIST-1 planets orbit in a plane around their star that is almost perfectly edge-on to us, we can witness many PPOs, where effectively the two planets involved in the PPO and our detectors are all in a direct line.

Related: How AI is helping us search the universe for alien technosignatures

Now suppose that transmissions from the planet being occulted are directed at the planet doing the occulting. These transmissions might be communications similar to those from NASA's Deep Space Network (DSN), in which large radio transmitters in Canberra, Madrid and California keep in constant touch with our fleet of interplanetary spacecraft. Similarly, it is possible that during a PPO, when two planets and ourselves are in a line, we could pick up leakage from radio transmissions between the two planets from the alien equivalent of the Deep Space Network. That's what this latest survey of TRAPPIST-1 was hunting for.

"TRAPPIST-1 is the ideal laboratory because it has known transiting planets, nearly perfectly edge-on, and it’s so close that we have enough sensitivity to detect certain signals," said Tusay.

No signals were detected, but we needn’t be downhearted. 

That's because the Allen Telescope Array is only sensitive enough to detect interplanetary transmissions at TRAPPIST-1 that are being broadcast with a power equivalent to an Arecibo-sized transmitter. Before it collapsed in 2020, the Arecibo radio telescope was a 305-meter (1,000-foot) dish. However, a powerful transmitter such as Arecibo would be “overkill” for interplanetary communications, said Tusay. The telescopes of the DSN are smaller in comparison with a lower effective power — too low for the Allen Telescope Array to detect. However, when it begins science operations towards the end of this decade, the Square Kilometer Array in South Africa and Australia should have the sensitivity to detect DSN-level transmissions during PPO events.

The Allen Telescope Array experiment has now shown that this PPO method is feasible. The ATA observed seven PPO events during the 28 hours it spent gazing at TRAPPIST-1 in 2022. In total it detected 25 million radio signals during that time.

"Most of that is radio frequency interference (RFI) from our own communications, so we needed to filter that out," said Tusay.

Radio frequency interference (RFI) is the terrestrial background of radio signals on Earth, from mobile phones to airport radar. In order to remove RFI from the observations more easily, Tusay developed something called the NBeamAnalysis pipeline. It is computer code that is able to distinguish signals that come only from the target, in this case TRAPPIST-1, from RFI that is seen in other directions in the telescope's field of view. By doing so, the code was able to whittle the 25 million signals down to just 2,264 that required further attention from a human being.

"Instead of looking through tens of millions of hits by eye, I only have to look through a few thousand, and most of them are still obvious to the human eye as RFI," said Tusay.

Ultimately, all the detected signals during the TRAPPIST-1 observations were RFI, but there are reasons why the Allen Telescope Array should keep looking. Although we can only guess as to the nature of an alien communication system and how often non-Earth beings would communicate with neighboring planets, comparing their signals to our own Deep Space Network is a starting point. Tusay's team estimates that the DSN is transmitting to Mars about a third of the time, meaning, on average, aliens would have to watch three PPO events of Earth and Mars to spot us sending a signal to one of our spacecraft around the Red Planet. If aliens are following a similar cadence at TRAPPIST-1, we'd have to watch at least three PPO events of each combination of planets to stand the best chance of spotting them.

This raises a question: Could aliens be watching for PPOs of planets in our own solar system? Those would happen more infrequently than in the TRAPPIST-1 system, where the planets are so close to their star that they orbit in a matter of a few days. Conversely, PPOs of Earth and Mars would take place approximately once every two years. In order to see a PPO of Earth and Mars, aliens would also have to be on a planet orbiting a star that is in the ecliptic on the sky, because the ecliptic is the plane of our solar system, and only by seeing this plane edge-on would they see any transits or occultations.

Nevertheless, "I know that searching for evidence that our own DSN transmissions have been picked up is an active area of investigation by other SETI scientists,” said Tusay. "I personally think that search strategy has merits."

In the meantime, we must keep listening to the sky — and thanks to these new observations of TRAPPIST-1, we at least now have a better idea of the best times during which to listen.

The findings are described in a paper that has been accepted for publication in The Astronomical Journal, and there is a pre-print available on arXiv.

This notion, along with the discovery that habitable worlds are common throughout the cosmos, has influenced a question that has perplexed scientists and others for decades: "Why is the universe so quiet?" This conundrum, which is said to have been proposed by physicist Enrico Fermi in 1950, is known as the Fermi paradox. If our solar system is young compared with the rest of the universe and humans could be capable of interstellar travel someday, shouldn't we have seen signs that other intelligent entities have spread throughout the cosmos by now? Basically, where are the aliens?

Perhaps we haven't encountered alien civilizations because there's a "universal limit to technological development" (ULTD) for every intelligent species in the universe and this limit sits well below a civilization's ability to colonize an entire galaxy, Antonio Gelis-Filho, a researcher in public policy at the Getúlio Vargas Foundation at the School of Business Administration (FGV EAESP) in Brazil, proposed in a recent paper published in the journal Futures. 

"If the ULTD hypothesis is correct, there has never been, there is not and there will never be something like an interstellar civilization, or anything similar to an 'interstellar conversation,'" Gelis-Filho told Space.com in an email. 

Related: Are we alone? Intelligent aliens may be rare, new study suggests

Based on the history of the rise and fall of human civilizations, the feasibility of constructing and running scientific projects that expand our knowledge and technology, and the apparent lack of technological intelligence elsewhere in the cosmos, Gelis-Filho thinks we should be careful about assuming the technological capacities of humans and other intelligent beings are limitless. 

The "uncrossable gap" 

Nobel prize-winning physicist Richard Feynman once said, "What I cannot create, I do not understand." The most straightforward interpretation of this is that our technology — what we can create — is constrained by our knowledge. 

There are, of course, natural limits to human technology. We can't travel in a straight line faster than the speed of light, for example. There may also be natural barriers to human knowledge — facts about the universe that are forever inaccessible to us due to the configuration of our biology. Sure, we have created technology that scaffolds our senses and cognition: Microscopes let us peer into the world of the small, telescopes provide a window into the world of the big, and computers crunch numbers and data that our individual minds are incapable of processing. 

However, the technologies and experiments that allow us to expand our knowledge are coming at an ever-increasing price. Projects like the Large Hadron Collider at CERN ($4.75 billion to construct and $286 million annually), the International Space Station ($3 billion per year), and the international effort to achieve nuclear fusion at ITER (an estimated $18 billion to $20 billion for construction) show that human efforts to probe our scientific horizons require increasing energy and resources. 

"If we are candid about it, the fact is that the last major fundamental advances in the science of the universe (macro- and micro-realms, cosmology and quantum mechanics) are almost a hundred years old," Gelis-Filho said. 

Sure, black holes and other phenomena are much better understood today than they were a century ago, but their theory is nowhere as consequential to human technology as relativity and quantum mechanics have been, Gelis-Filho contends.

Just "compare the scientific evolution from 1830 (no theory of evolution, no theory of electromagnetism) to 1930 (relativity and quantum mechanics already there) and from 1930 to 2024 (still no unifying theory) for us to perceive that the rate of advancement is slowing, to say the least," Gelis-Filho said. "Low-hanging fruits have already been picked. The remaining ones seem to be hanging from impossibly high branches." 

The growing price of probing the frontiers of human knowledge means we might decide the price is too high. Indeed, the European commission recently abandoned its plan to select a number of billion-euro flagship research projects, which included plans to convert solar and wind energy into fuels, and to bring cell and gene therapies into clinical settings. In such a case, the development of new technologies that leverage new breakthroughs in our understanding of reality will also come to a standstill, along with our dreams of becoming an interstellar civilization. 

Any intelligent civilization in the cosmos will have to face this same scenario, Gelis-Filho said. At a certain point, no matter how ingenious they become, they will have to make a decision: Do we build a particle accelerator as large as the Milky Way to test our new unifying theory, for example, or do we build necessary infrastructure for our civilization's survival? 

The ULTD hypothesis sustains that, even if a civilization decided to build such a machine to test the limits of their knowledge, they would discover that the levels of energy needed to perform experiments to facilitate a leap in scientific knowledge do not increase linearly. They would reach a point where their current technology would not allow them to cross the gap between one level and the next. 

"Since the laws of physics are the same throughout the universe, every single civilization will eventually clash against that 'uncrossable gap,'" Giles-Filho said. 

The cost of increasing societal complexity  

Gelis-Filho also thinks lessons from the rise and fall of human civilizations can be applied to this astrobiological context. Complex societies expand by adding layers of societal complexity to produce more "energy" to keep growing. However, after a certain point, complexity does not "pay for itself," and its returns will decrease, he said. 

"If we think of a hunter-gathering society, the number of social roles (chief, hunter, collector and so on) is minimal; in the Late Roman Empire, it was much higher and in our industrial society it is immensely higher," Gelis-Filho explained.

Of course, with added specialization, more complex societies can produce more. As people developed agriculture on Earth, for instance, the influx of food provided by the new technology led to new societal roles aimed at increasing production further. But as the level of complexity increased, so did the need for costly infrastructure to support it.  

Related: First contact with aliens could end in colonization and genocide if we don't learn from history

Gelis-Filho borrows his argument from Joseph Tainter, an archaeologist who studied many complex societies throughout history. Tainter  hypothesizes that, although the fatal blow to a society may vary (e.g., war, drought, epidemics or an astronomical event), the root cause is always the same: decreasing returns on complexity that have made the society fragile. 

"I have applied the concept to any technological society anywhere in the universe," Gelis-Filho said. "Advanced spatial technology demands legacy infrastructure to be developed. That infrastructure is just a part of societal complexity. … It is possible that many non-terrestrial societies have collapsed because of diminishing returns on societal complexity, even before clashing against the limits imposed by energy requirements to test scientific theories."

Cosmic messages in a bottle 

Despite all of this, Gelis-Filho doesn't rule out the possibility of receiving a message or signal from another intelligent civilization. The universal limit to technological development prohibits technological development beyond a level that prevents the organized, self-sustaining spread of a civilization beyond its solar system. 

"However, it does not preclude the existence of 'castaway technology,' like wandering dead space probes (just think about the Voyager 1 in a hundred thousand years, silently crossing our galaxy), isolated messages being received (the Wow! signal being a candidate) or even 'alien dead Voyagers' being retrieved by us (however improbable that event is)," he said. 

Such attempts to communicate with other intelligent civilizations across the vastness of space resemble "great cosmic bottle messages" — like a stranded captain of a sunken ship on a remote island trying to signal to the outside world with the rudimentary tools they have, Gelis-Filho explained. 

Giles-Filho's hypothesis is one possible explanation for why our attempts to observe an interstellar civilization have fallen short. Yes, we have been searching for signs that we are not alone in the cosmos for only a few decades. Maybe we haven't been looking long enough, in the right place or even for the right thing. The unambiguous detection of an intelligent alien civilization would obviously prove the ULTD hypothesis wrong, as would the sudden leap in knowledge that could facilitate the expansion of human civilization into the stars. Until then, the ULTD hypothesis provides a sobering reminder that our species' destiny is not a given.

Nathalie Cabrol's book, "The Secret Life of the Universe: An Astrobiologist's Search for the Origins and Frontiers of Life" (Scribner/Simon & Schuster), released last month, offers an insightful and reflective view of the search for life — a mind-stretching quest not only looking "out there" but also right here on Earth.

Perhaps part of the challenge is that humankind is both the observer and the observation, Cabrol explains. That is, we are life trying to understand itself and its origin. "We are reminded that the universe is both an enigmatic puzzle and a profound mirror reflecting our own existence," Cabrol writes.

Nathalie Cabrol is a French-American explorer and the director of the Carl Sagan Center for Research at the SETI Institute in Mountain View, California. In an exclusive interview, Space.com discussed with her the new book and the professional odyssey that she has embarked upon.

Space.com: Your book consists of a dozen unique chapters - is there a theme linking them? Perhaps in those subjects you tackled, you were on your own personal journey to help recognize the issues surrounding the are we alone question?

Nathalie Cabrol: The questioning behind every single chapter is that we're looking for something that we don't understand. It's a point of reference that this is us. And that's okay. It doesn't matter that we don't have the answers. Because if we had the answers we wouldn't make the journey.

Space.com: So that journey is one that's open-ended in that we should standby for surprises?

Cabrol: The chapters are the journey. Each one helps you see a different perspective, a different angle, shine a different light on a question. I am not necessarily buying the way we're going after life in the universe right now. I'm very vocal about this. But this is where we are and this is what we have. The missions are telling us that the stuff we're made of is not an accident. It's almost common out there. I wanted to share at the same time there are unanswered questions … show there might be other ways of exploring for life.

Space.com: You write about Mars and the long saga of looking for life on the Red Planet. In particular, flagging the Viking Labeled Release (LR) experiment of the 1970s, results that you say today are still deemed inconclusive.

Cabrol: Yes, it's inconclusive and just another acknowledgment that five decades later you have people thinking that it showed that life was there on Mars. We have today evidence those results could be achieved without life and by the environment alone. That [evidence] says we didn't demonstrate that life was there. You have to prove that the environment alone didn't yield those LR results. Environment and life … how do you detangle the two and come up with an unambiguous signature of life? When life is somewhere, you don't have one or the other anymore. You have co-evolution, a mixed thing, a living world.

Space.com: Is the search for Mars life a template, a teaching tool, for looking for life elsewhere? 

Cabrol: It depends on the scenario you are choosing. Scenario 1 is that life never appeared on Mars, period. The problem for us will be to demonstrate that. In science this is the hardest one — when do we pull the plug and just admit that there's no life on Mars and we're sure of that.

Scenario 2 is Mars has life, but unfortunately somehow we contaminated each other through planetary exchange. So it's likely to be related and not teaching us much about other types of life. 

Scenario 3 is that life on Mars is found to be a separate genesis. 

Mars can teach us general rules of looking for life elsewhere, and especially the relationship between life and the environment. It will teach us general rules of co-evolution for sure. Can it teach us how to search for life on Titan or on Venus? I don't think so. Those environments are so different.

Space.com: There is on-going and growing interest in Venus being a hot-bed for life.

Cabrol: If we discover life on Venus then it's extraordinary because this is pretty much the anti-Earth, a dry, super hot, super acidic environment. But the point is that we're exploring those worlds and we're learning about very different potential co-evolution. We are looking for complexity of life informing its environment and the environment informing life.

Space.com: Another thing struck me when reading your book: We're all youngsters when it comes to trying to put the puzzle pieces together about the search for life.

Cabrol: We are so young. I was born in 1963. Just a few years before that all we knew about the universe came from ground-based telescopes. My childhood [saw the] Mariner spacecraft hurled to Venus and Mars. Since then, just in 60 years, everything has literally taken off. 

We are very young and the search for extraterrestrials is the same thing. We're just starting to learn what the universe is about, the diversity. What people are missing is the iteration of science. You ask a question. You build an experiment. You go and test it. Then you have the science and it's nothing like what you have predicted. Now you have to scramble and make sense of it. Develop another hypothesis. Build more experiments and test it. And this is what we're doing.

Space.com: When do you think we will find life?

Cabrol: I do get the question all the time. 

I will tell you that we are close. I really do think we are close. Exoplanets are going to be a tricky one. They are so far away. We don't know where life is and we cannot bring back samples right now. Perhaps finding traces of pollution and synthetic molecules could happen, to make sure we're finding life. 

As for SETI, it could come anytime and anything could land on our planet at any time too.

Space.com: And that brings me to your chapter, "Connecting Blue Dots" which includes a look at unidentified flying objects (UFOs), now rebranded in some circles as unidentified aerial phenomenon, or UAPs. 

Cabrol: We're looking for aliens in the kind of world that we understand, a world of space and time with the laws that we know. And in a universe of space and time, there's a lot to be said about sending robots, that the first encounter will be the technology of a different species. If they are organics like us, then they are fragile like us. 

At this point what absolutely fascinates me is the Venn diagram between astrobiology, neuroscience and quantum physics. Consciousness is a function of the brain, but perhaps the brain might just be the computer that you need to get to something that is much bigger and larger. 

Experts in these areas are talking with each other and there are very interesting conversations going on. And this has incredible implications for the search for life elsewhere in the universe. There are immediate implications for how we treat life on Earth, meaning everything that is alive on this planet is conscious. 

I am watching this with great interest.

Space.com: In your book, you paraphrase a comment from the late Carl Sagan that, as a scientist, "I do not want to believe. I want to know."

Cabrol: My message throughout this book is that what we have now is absolutely mind boggling. It's not only searching for life in the universe, it is also understanding how this search will actually mirror how we understand ourselves, our place on the planet, our relationship with the world and the universe around us. 

They were attending this year's annual Breakthrough Discuss conference — a meeting of the minds to unravel how artificial intelligence, astrobiology and space missions may one day come to redefine our understanding of life and humanity's relationship to the cosmos. 

"This was the first time we had the Breakthrough Discuss conference outside the U.S. It speaks to how technosignature science is becoming more universally accepted across universities. It's now a part of mainstream astrophysics," Vishal Gajjar, search for extraterrestrial intelligence (SETI) investigator and project scientist for Breakthrough Listen's international collaboration, told Space.com.  

The conference is associated with other "Breakthrough" initiatives, including the Breakthrough Listen Project, which is a 100 million dollar program that will use some of the world's most advanced telescopes to search about one million nearby star systems for signs of technologically advanced civilizations. Another initiative, Breakthrough Watch, is aiming to characterize a number of Earth-size rocky planets within 20 light-years of Earth to accomplish the same goal of finding life beyond our world. The Discuss conference provides a platform for researchers working in different fields of astrobiology to compare and discuss their work, and to speculate on what the future of this exciting field might hold. 

Related: Could AI find alien life faster than humans, and would it tell us?

The hot topic of this year's conference centered around how artificial intelligence tools can help comb through massive sets of data generated by telescopes and other observatories to identify any indications that we are, in fact, not alone in the universe. 

Historically, scientists with the search for extraterrestrial intelligence (SETI) institute — an organization that focuses on the search for extraterrestrial life —  have had to decide where to look for signals as well as what type of signals to look for in the first place. How would a sufficiently technologically advanced civilization alert their presence to anyone out there listening? How would we locate any such messages? The answers to these questions — answers that would mark the starting point of any quest to find advanced alien life — have been, at best, educated guesses thus far.

But maybe that doesn't need to be the case going forward. 

New developments in artificial intelligence and improved levels of observational capabilities mean enormous volumes of data can be captured and sifted through at record rates. And these advancements, perhaps, may resolve some of the current limitations in how SETI scientists conduct their searches. Rather than taking observational stabs in the dark, it might now just be a matter of waiting for something unexpected. 

Where to look? 

Which part of the sky should a typical technological signature (or technosignature) search focus on? 

This has been a question SETI investigators have sought to answer because, as time and resources are limited when it comes to having access to large and expensive telescopes, investigators want to give themselves the best chance at spotting something potentially interesting. 

Largely thanks to funding, as well as new observatories that capture data from large areas of the sky simultaneously, SETI investigators are overcoming some of these limitations when it comes to the "where" in this equation.

"We are surveying almost a million nearby stars identified by the Gaia mission," Gajjar told Space.com. 

Launched in 2013, Gaia is a space-based telescope that's creating a catalog of over one billion stars in the Milky Way. From this catalog, SETI investigators identified one million nearby stars of various sizes and luminosities to keep track of using some of the world's most powerful ground-based radio and optical telescopes, including the Green Bank Telescope, Parkes Observatory and the MeerKAT Array. 

Scientists aren't only restricting themselves to stars, though. It's possible that a technosignature could come from empty space — from an object that isn't a star or planet but rather something like a spacecraft or probe that might be broadcasting a signal. "We are also broadly looking at the entire galactic plane of the Milky Way and the galactic center as well, where there is the highest concentration of stars," said Gajjar. 

But new technologies can also create new problems. 

When we are searching with such a large number of targets, and therefore collecting such a large volume of data, it's inevitable that we'll generate a massive number of false positive detections from our own technology. For instance, in terms of electromagnetic waves, human technology is constantly producing signals (phone towers, airplanes and drones, to name a few) and these local interferences are also picked up by scientists' technosignature detection mechanisms. So, separating our own signals from those of a potential extraterrestrial source becomes a real challenge. 

Gajjar explains that researchers have successfully been able to train artificial intelligence models on raw data that has been collected so far (which is full of local false positives), so the model can effectively eliminate these signals, reducing the amount of "noise" that researchers must shift through to find interesting signals. "With AI we have been able to remove 99.8% of our own signals," said Gajjar. 

What to look for?  

Deciding what a "typical" technosignature should look like is difficult because, as humans, we may assume another technologically advanced civilization would create a signal with characteristics we use to allude to our own existence. For example, a probe like Voyager 1, or broadcasting radio waves into space. 

However, we ought to get away from our anthropocentric way of thinking. "So far we have been limited in our imagination of what these technological signatures might look like," Gajjar said. 

There are still legitimate scientific reasons, though, why scientists think a signal should have certain features. "Our main argument has to do with energy," says Gajjar. If a civilization wanted to create a "beacon" to disclose its presence, for example, it makes sense that they would want to create a signal that stands out — but doesn't cost extreme amounts of energy to create. 

Consider a signal that taps into the electromagnetic spectrum, the continuum of various wavelengths and energies of radiation. The shorter the wavelength, the more energy is required to generate a signal within its range. It would thus cost a civilization vast amounts of resources to generate a unique signal in the gamma band of the spectrum, but way less to create one in the radio band. On the other hand, though it sounds extreme, what if an extremely advanced civilization could actually move a whole star in such a way that they form unique gravitational waves? Generating ripples in the fabric of spacetime by moving a massive object to alert the rest of the universe to your presence would be astounding of course, but it would take mind boggling amounts of energy to do — according to the physics we know about, at least.

If the signal is too low in energy, though, it can get lost among the background of other electromagnetic sources in the galaxy — so, theoretically, radio signals may not be the optimal way to go despite the relative ease with which they can be generated. "But even within that boundary, there is still a vast amount of possible ways a signal could look," says Gajjar. 

For instance, it also might not be the case that we detect "beacon" signals where a civilization wants to be seen. It could be a "leakage" signal, where we intercept communication intended for a civilization's own internal communicative purposes (our own radio signals are leaking into space in this way, in fact). So, if we want to be agnostic about what a signal could look like, Gajjar says we need to simply search for anomalies. All of them. 

And this is where artificial intelligence comes in.

Researchers have been developing artificial intelligence models capable of identifying anomalous signals in vast astronomical datasets generated by surveys like the ones mentioned earlier. These models work in similar ways to how large language models (LLMs), like ChatGPT, work. LLMs basically predict the most likely word to follow another in a sentence based on large quantities of data, and these anomaly-detectors predict what electromagnetic signals are most likely to follow based on previous observational data.

If you take hundreds of hours of observational data that you have already gathered, and then you train an AI to make probabilistic predictions about what electromagnetic signals should happen next, and then if the new data violates what the AI predicts, that could be considered an anomaly. 

"Machine learning algorithms in particular have proven effective at detecting anomalies but humans still have a crucial role to play," Michelle Lochner, an astrophysicist who also spoke at Breakthrough Discuss, and who develops anomaly detection algorithms told Space.com. It's then the job of astrophysicists to develop an explanation for what could be the cause of this anomalous signal.  

The future

While galactic surveys are already generating large quantities of data for SETI investigators to sift through, even more are on the way. Next year, the Vera C. Rubin Observatories Survey of Space and Time will begin operations and is expected to generate 20 terabytes of data every single night (60 petabytes over 10 years), and ultimately provide “32 trillion observations of 20 billion galaxies.” 

In addition, the Square Kilometer Array, which will exceed the image resolution of Hubble by 50 times, is slated to open in 2028. 

There will be computational challengers for astronomers seeking to identify new potential  targets in large data sets created by current and future observatories, however, "the possibilities for scientific discoveries are enormous and, by combining large datasets, sophisticated AI algorithms and human insights, this may be the time for one of the most important discoveries in human history," said Lochner. 

Gajjar says he is also excited about the future of technosignature science. 

"When Breakthrough Listen started, it changed the whole game and opened up this new area of research and triggered so many opportunities across the world - it's being funded at all levels of academia which was certainly not the case when I finished my P.H.D!"

Technosignature science appears to have entered the mainstream. Researchers wanting to enter the field are finally being taken seriously, and new avenues for funding as well as emerging technologies are turning what was once a field for retired astrophysicists into a respected scientific pursuit. 

"Searching for technological signs of aliens', can sound a bit absurd to say, but why build multibillion dollar telescopes if we can't even check to see if there is another advanced civilization out there? They might even want to say hi."

Conducted with the Murchison Widefield Array (MWA) in Australia, the search concerned itself with low radio frequencies in the 80–300 MHz range. For comparison, SETI (which stands for Search for Extraterrestrial Intelligence) typically looks for alien signals in the 1,420 MHz hydrogen emission frequency. In fact, low frequencies are relatively unexplored real estate for SETI.

The search was conducted by Chenoa Tremblay of the SETI Institute in California and Steven Tingay, the director of the MWA from Australia's Curtin University. The team focused on a 30-degree field of view in the constellation of Vela, the Sails, encompassing 2,880 galaxies. The redshifts, and hence distances, to 1,317 of these galaxies have previously been measured with high accuracy — so, Tremblay and Tingay targeted these galaxies in particular. By knowing the galaxies' distances, the duo could place constraints on the power of any transmitters in those galaxies.

While their initial search failed to detect an extraterrestrial signal, Tremblay and Tingay concluded in their paper that they would have been capable of detecting one with a transmitter power of 7 x 10^22 watts at a frequency of 100MHz.

"This work represents a significant step forward in our efforts to detect signals from advanced extraterrestrial civilizations," said Tremblay in a statement. "The large field of view and low-frequency range of the MWA makes it an ideal tool for this kind of research, and the limits we set will guide future studies."

Related: Are we alone? Intelligent aliens may be rare, new study suggests

For much of its 64-year history, SETI has focused on stars in our own Milky Way galaxy — in recent years, however, the net has begun to widen.

In 2015, for instance, the Glimpsing Heat from Alien Technologies (G-HAT) project surveyed 100,000 galaxies with NASA's Wide-field Infrared Survey Telescope (WISE) in search of civilizations that may have built "Dyson swarms" around all the stars in their respective galaxies. None were found. In 2023, a team led by Yuri Uno of the National Chung Hsing University in Taiwan suggested that there could be no more than one civilization within three billion light-years of us that's pointing a radio transmitter with a power above 7.7 x 10^26 watts at the Milky Way.

The same year, Michael Garrett of the Jodrell Bank Center for Astrophysics and Breakthrough Listen's Andrew Siemion conducted a search of background galaxies to constrain the maximum detectable power, arriving at a range of about 10^23 watts to 10^26 watts. (The exact maximum power for a potential signal would depend on the distance to the galaxy in which it originates.) Finally, the SETI Institute's Carmen Choza led a team that recently conducted a targeted search of 97 galaxies with the Green Bank Telescope — but detected nothing.

Where would so much power come from?

To achieve these transmitter powers, technological aliens would have to harness the power of a star, or perhaps even several stars. 

In 1964, the Soviet astronomer Nikolai Kardashev developed a classification scale for extraterrestrial civilizations based on how much energy they have at their disposal. A type 1 civilization would harness all the energy available on one planet, generalized as 10^16 watts or greater. A type 2 civilization would be able to harness the power of an entire star, which would be 10^26 watts for a sun-like star. And a type 3 civilization would be able to utilize the entire power output of every star in its galaxy, amounting to about 10^36 watts.

The null detections so far do not necessarily mean that technological, communicative extraterrestrial life does not exist, just that our observations are not comprehensive enough yet to say anything about its existence either way. We simply aren't sure. Estimates suggest there are up to 2 trillion galaxies in the observable universe and we have only searched a small fraction of them, and for only a short period of time. 

Running an intergalactic radio beacon would also not be cheap; it's possible any radio beacons were switched off to conserve power when we looked. Or, perhaps they were pointed in the direction of other galaxies. Maybe Kardashev type 2 and 3 civilizations are rare, meaning we wouldn't see transmitters with those powers so, per the constraints, the radio beacons might be out there but operating at a power less than our ability to detect. Furthermore, this new survey operated at low frequencies — but transmitters at higher frequencies cannot be ruled out.

Tremblay and Tingay point out that several powerful radio emitters on Earth, as well as some of our earliest transmissions, are at low frequency — thus justifying the search within this range. Plus, given the relative dearth of SETI searches at these low frequencies, there is always the chance of finding something unexpected. For SETI to succeed, radio searches have to cover a multitude of frequencies to make sure that we don’t miss that elusive signal. 

"Continuing to work together to cover the frequency space will be crucial in the future," conclude Tremblay and Tingay in their paper.

The study was published on 26 Aug. in The Astrophysical Journal.

A common axiom in the search for extraterrestrial intelligence (SETI) is that if we do detect technologically advanced aliens, there are probably many, many instances of alien life out there rather than there just being two cases (us and the new discovery).

In a new paper, astronomers David Kipping of Columbia University in New York and Geraint Lewis of the University of Sydney describe how this logic works, based on a probability distribution first introduced by the biologist and mathematician J. B. S. Haldane in 1932. Let's imagine a bunch of Earth-like exoplanets, all with similar characteristics. Given their minor differences, we would expect life to arise either on all of them or on none of them; there's no obvious reason why half of these near-identical planets would support life and half wouldn't, for example. 

We can then display the various outcomes in a U-shaped graph, with the probability on the y-axis and the fraction of planets with life on the x-axis. The two prongs of the U-shape correspond to none or very few planets with life, and lots of planets with life. The valley of the U-shape, which corresponds to a low likelihood, represents half the planets having life.

Related: Drake Equation: Estimating the odds of finding E.T.

Now Kipping and Lewis have ascribed Haldane's logic to the famous Drake equation. Developed by astronomer Frank Drake prior to the first-ever SETI conference, at Green Bank Observatory in 1961, as a means of providing the workshop with an agenda, the Drake equation has subsequently taken on a life of its own, being used to estimate the number of technological lifeforms in the Milky Way galaxy. 

The Drake equation is written as N = R* x fp x ne x fl x fi x fc x L, where N is the number of civilizations, R* is the star-formation rate, fp is the fraction of stars that have planets, ne is the number of planets that are potentially habitable, fl is the fraction of those potentially habitable planets that evolve life, fi is the fraction that develop "intelligent" life, fc is the fraction that have communicative life, and L is the average lifetime of civilizations.

Astronomers know the star-formation rate (less than 10 solar masses per year in our galaxy) and the fraction of stars that have planets (almost every star has planets) very well. The number of potentially habitable planets is less well known, but astronomers are learning more about them every day as they probe exoplanetary atmospheres with the James Webb Space Telescope and characterize those worlds. The values of the other four terms remain a complete mystery, which renders any attempts to use the Drake equation less than satisfactory because so much of it is guesswork.

However, Kipping and Lewis point out that the first six terms in the Drake equation describe the "birth" of what they call extraterrestrial technological instantiations, or ETI. This is how they refer to technological alien life, neatly sidestepping terms such as "civilizations," "species" and "intelligence," which have not only proven problematic (for example, how do we define intelligence?) but may also be inaccurate when describing alien life. Meanwhile, the final term, L, relates to the "death," or otherwise the disappearance, of ETI. 

Splitting the terms of the Drake equation this way has allowed Kipping and Lewis to simplify the formula, to read: The time-averaged number of ETIs in the galaxy equals the birth rate of ETIs multiplied by their death rate. 

"The beauty of our approach is that it is totally general," Kipping told Space.com. This means that there is no need to have to worry about the terms of the Drake equation that we don't know. 

"We are not assuming any particular mechanism or means of birth," added Kipping. "The births could occur via spontaneous emergence, or panspermia seeding, or empire building or whatever else you want — there simply is a birth rate."

Kipping and Lewis assume what they call a steady state Drake equation, where there is a roughly equal level of birth and death rates in an equilibrium that is inevitably reached once enough time has passed. The two astronomers then relate this back to Haldane's prior (a "prior" is the name for a type of probability distribution, such as the U-shaped curve) by way of a characteristic called the occupation fraction, F. In the exoplanet example mentioned earlier in this article, a high value of F — close to 1 — would correspond to every planet having life, and a low value — close to or equal to 0 — would relate to no planets having life.

The problem facing SETI scientists is that, based on observations so far, F probably is not near 1; otherwise, we would have noticed by now that we are not alone, assuming that intelligent aliens are proficient at spreading across the galaxy, building megastructures such as Dyson swarms and beaming out radio signals. This means that, if we really are not alone in the universe, then the occupation fraction must be closer to 0.5, placing it in that unlikely valley of the U-shaped curve. Based on that U-shape, it is likely that we are relatively alone — that technological life elsewhere in the universe is rare. 

"These are instances of life who become obvious, firstly through the signals they produce and then through their colonization where they would be seen through megastructures," Lewis told Space.com. "If such an ETI had arisen in the life of the Milky Way, then they could have colonized the entire galaxy in 10 million to 100 million years, and even after they fall, then their debris would be around for a long time. The fact that we don't see anything out there means that if they did exist, they vanished long ago and their signatures have decayed away and we are back to our original premise — ETIs appear to be rare in time and space."

Related: The search for alien life

Yet Kipping and Lewis don't advocate giving up on SETI. If we ignore the lack of evidence for a moment, the steady state Drake equation predicts a crowded universe as being equally likely as one in which we are lonely. For a crowded universe, the occupation fraction must be close to 1, and perhaps this is still possible under certain circumstances. Maybe ETI stays in their own region, and our solar system just happens to be in a region that no one has spread into yet. That would mean the aliens are quite far away, and our strategy of searching for them around stars close by is the wrong one. These inhabited regions might be more clearly detected in other galaxies. "I certainly would advocate for extragalactic SETI," said Kipping.

Or perhaps interstellar travel and megastructure-building are too difficult, or maybe they are not even desired by an ETI living a more frugal, less colonial, existence. And with regards to a lack of a radio or optical signal detection, SETI has hardly had the resources to be particularly comprehensive in its search so far, and we could easily have missed a signal.

It's also possible that there is plenty of complex life, but that the development of technological life is rare.

There's also a chance that the birth and death rates of ETI have not reached a steady state after all, meaning that there would be still time for new ETI to arrive on the scene and increase the occupation fraction. Given the age of the universe and the finite lifespan of an ETI, however, this seems unlikely.

The research is currently available as a pre-print, and has been submitted to the International Journal of Astrobiology for peer-reviewed publication.

Plate tectonics are absolutely essential if complex life is to evolve, argue Robert Stern of the University of Texas at Dallas and Taras Gerya of ETH Zurich in Switzerland. On Earth, complex multicellular life appeared during a period known as the Cambrian explosion, 539 million years ago.

"We believe that the onset of modern-day-style plate tectonics greatly accelerated the evolution of complex life and was one of the major causes of the Cambrian explosion," Gerya told Space.com.

Plate tectonics describes the process of continental plates, which are buoyed up on a molten mantle, sliding over one another, leading to subduction zones and mountains, rift valleys and volcanoes, as well as earthquakes.

Related: The search for alien life (reference)

The modern-day form of plate tectonics, say Stern and Gerya, only began between a billion and half a billion years ago, in a geological era known as the Neoproterozoic. Prior to that, Earth had what's known as stagnant lid tectonics: Earth's crust, called the lithosphere, was one solid piece and wasn't broken into different plates. The change to modern-day plate tectonics only happened once the lithosphere had cooled enough to grow sufficiently dense and strong to be capable of being subducted — that is, to be pushed under other parts of the lithosphere for a significant amount of time before being recycled back onto the surface where two tectonic plates are moving apart.

The environmental stresses that modern-day plate tectonics places on the biosphere could have instigated the evolution of complex life a little over half a billion years ago, as life suddenly found itself living in an environment where it was forced to adapt or die, creating an evolutionary pressure that pushed the development of all manner of life that existed in the oceans and on the dry land associated with the continental plates. Given that kickstart, life eventually — through no design or evolutionary imperative other than natural selection — ended up evolving into us, the idea goes.

"The long-lasting coexistence of oceans with dry land seems critical for obtaining intelligent life and technological civilizations as the result of biological evolution," said Gerya. "But having continents and oceans is not sufficient on their own, because life's evolution is very slow. In order to accelerate it, plate tectonics is needed."

However, there's a problem. Earth is the only planet in the solar system to have plate tectonics. What's more, models indicate that plate tectonics could be rare, especially on a class of exoplanets known as super-Earths, where the stagnant lid configuration could dominate.

Coupled with the need for plate tectonics is the need for oceans and continents. Models of planetary formation indicate that planets covered entirely in oceans dozens of miles deep could be common, as could desert worlds with no water at all. Earth, with its relatively thin veneer of ocean water and topography that allows continents to rise above the oceans, seems to occupy a sweet spot that is carefully balanced between the two extremes of deep ocean planets and dry desert worlds.

Having oceans is crucial because it is strongly suspected that life on Earth began in the sea. Land is also critical, not only for providing nutrients via weathering and facilitating the carbon cycle, but also for enabling combustion (in concert with oxygen) that can lead to technology when harnessed by intelligent life.

If planets with plate tectonics, as well as the right amount of water and land, are rare, then technological, communicative, alien life may also be rare.

"What we have tried to explain is, why have we not been contacted?" said Gerya.

Related: Fermi Paradox: Where are the aliens? 

To illustrate this, Gerya and Stern used the Drake equation. Devised in 1961 by the late SETI pioneer Frank Drake, it was intended to provide an agenda for the first-ever SETI (search for extraterrestrial intelligence) scientific conference, held in that year at the Green Bank Observatory in West Virginia, by summarizing the various factors required for the development of technological civilizations, resulting in an estimate of the number of extraterrestrial civilizations that might exist. However, it should be noted that the Drake equation is more of a thought experiment to highlight what we know and what we don't know about the evolution of technological life, rather than an absolute guide to the number of civilizations out there.

"Previous estimates for the lower limit of the number of civilizations in our galaxy were rather high," said Gerya.

One of the terms of the Drake equation is fi, the fraction of exoplanets that develop intelligent life (how we define "intelligence" in this context is still debated, but the modern way of thinking includes all intelligent animals, such as chimps and dolphins). Stern and Gerya argue that fi should be the product of two more terms, specifically the fraction of planets with both continents and oceans (foc), and the fraction of planets with long-lasting plate tectonics (fpt).

However, given the apparent rarity of plate tectonics, and worlds that can have oceans and continents, Stern and Gerya find that fi is a very small number. They estimate that just 17% of exoplanets have plate tectonics, and the proportion with just the right amount of water and land is likely even smaller — between 0.02% and 1%. Multiply these together and they give a value of fi as between 0.003% and 0.2%.

Then, by plugging this value into the Drake equation, Stern and Gerya arrive at a value for the number of extraterrestrial civilizations as somewhere between 0.0004 and 20,000. That's still quite a large range, the result of the other terms in the Drake equation not being known well, if at all. However, it is still orders of magnitude less than the value of a million civilizations that Drake predicted in the 1960s.

"A value of 0.0004 means that there could be as few as 4 civilizations per 10,000 galaxies," said Taras.

There are several caveats to all this. One is, as mentioned, that some of the other terms of the Drake equation such as the fraction of planets that evolve life in the first place, the fraction with intelligent life that develops technology and the lifetime of those civilizations are completely unknown. If their values turn out to be extremely high — for example, if civilizations typically survive for billions of years — then the chances of more of them being around now will increase.

Another caveat is that while, in general, life as we know it needs plate tectonics, oceans and land to evolve and thrive, it is possible to imagine scenarios where technological, ocean-dwelling life that never steps foot on land could evolve. However, these would be specific cases, outliers that are the exception to the rule.

There's also a risk of jumping the gun when saying that we haven't been contacted yet. SETI astronomer Jill Tarter is fond of saying that if, the galaxy were an ocean, we'd have searched only a cup's worth of it. While the search has accelerated recently thanks to the ambitious Breakthrough Listen project, the point still stands. We've not searched every star yet, and those that we have searched, we have not listened to or watched for very long. We could easily have missed an extraterrestrial signal.

A final point to consider is that of the "Great Filter." This is a concept first proposed by the economist and futurist Robin Hanson, which suggests that there might be some universal bottleneck in the evolution of all life that prevents technological civilizations from existing. In Stern and Gerya's model, that bottleneck is provided by the lack of plate tectonics, oceans and continents. However, despite their estimate for the number of civilizations being low, it is non-zero, and there is a school of thought that plays into the Copernican principle, which states that Earth should not be treated as special and is just another planet orbiting a humdrum star. Therefore, if life can evolve on Earth, it should be able to evolve on many planets, because Earth shouldn't be special. The question then becomes, At what point does the Great Filter kick in?

Related: Why haven't aliens contacted Earth? New Fermi Paradox analysis suggests we're not that interesting yet

Perhaps Stern and Gerya have jumped the gun, declaring that planets with plate tectonics and just the right amount of water and land are rare, before we have the observational evidence to support that statement.

"Of course, it would be ideal to have observational data on how common continents, oceans and plate tectonics are on exoplanets," said Gerya. "Unfortunately, this is far beyond our current observation capacities. On the other hand, the planetary formation process is to some extent understood, and planetary formation models are capable of delivering predictions about what we can expect. Those predictions can be used to evaluate the probability of rocky exoplanets having continents, oceans and plate tectonics."

If Stern and Gerya are correct, then we could very well be effectively alone in the universe. If that's the case, we have an enormous responsibility to shoulder. "We should take all possible care to preserve our own — very rare! — civilization," said Gerya. Otherwise, we could kill ourselves off and render extinct the only technological life in our Milky Way galaxy.

Stern and Gerya's analysis was published on April 12 in the journal Scientific Reports.

Michael Garrett is the Sir Bernard Lovell chair of Astrophysics and Director of Jodrell Bank Centre for Astrophysics, University of Manchester.

Artificial intelligence (AI) has progressed at an astounding pace over the last few years. Some scientists are now looking towards the development of artificial superintelligence (ASI) — a form of AI that would not only surpass human intelligence but would not be bound by the learning speeds of humans.

But what if this milestone isn't just a remarkable achievement? What if it also represents a formidable bottleneck in the development of all civilizations, one so challenging that it thwarts their long-term survival?

Related: Could AI find alien life faster than humans, and would it tell us?

This idea is at the heart of a research paper I recently published in Acta Astronautica. Could AI be the universe's "great filter" – a threshold so hard to overcome that it prevents most life from evolving into space-faring civilizations?

This is a concept that might explain why the search for extraterrestrial intelligence (SETI) has yet to detect the signatures of advanced technical civilizations elsewhere in the galaxy.

The great filter hypothesis is ultimately a proposed solution to the Fermi Paradox. This questions why, in a universe vast and ancient enough to host billions of potentially habitable planets, we have not detected any signs of alien civilizations. The hypothesis suggests there are insurmountable hurdles in the evolutionary timeline of civilizations that prevent them from developing into space-faring entities.

I believe the emergence of ASI could be such a filter. AI's rapid advancement, potentially leading to ASI, may intersect with a critical phase in a civilization's development – the transition from a single-planet species to a multiplanetary one.

This is where many civilizations could falter, with AI making much more rapid progress than our ability either to control it or sustainably explore and populate our Solar System.

The challenge with AI, and specifically ASI, lies in its autonomous, self-amplifying and improving nature. It possesses the potential to enhance its own capabilities at a speed that outpaces our own evolutionary timelines without AI.

The potential for something to go badly wrong is enormous, leading to the downfall of both biological and AI civilizations before they ever get the chance to become multiplanetary. For example, if nations increasingly rely on and cede power to autonomous AI systems that compete against each other, military capabilities could be used to kill and destroy on an unprecedented scale. This could potentially lead to the destruction of our entire civilization, including the AI systems themselves.

In this scenario, I estimate the typical longevity of a technological civilization might be less than 100 years. That's roughly the time between being able to receive and broadcast signals between the stars (1960), and the estimated emergence of ASI (2040) on Earth. This is alarmingly short when set against the cosmic timescale of billions of years.

This estimate, when plugged into optimistic versions of the Drake equation – which attempts to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way – suggests that, at any given time, there are only a handful of intelligent civilizations out there. Moreover, like us, their relatively modest technological activities could make them quite challenging to detect.

Wake-up call

This research is not simply a cautionary tale of potential doom. It serves as a wake-up call for humanity to establish robust regulatory frameworks to guide the development of AI, including military systems.

This is not just about preventing the malevolent use of AI on Earth; it’s also about ensuring the evolution of AI aligns with the long-term survival of our species. It suggests we need to put more resources into becoming a multiplanetary society as soon as possible – a goal that has lain dormant since the heady days of the Apollo project, but has lately been reignited by advances made by private companies.

As the historian Yuval Noah Harari noted, nothing in history has prepared us for the impact of introducing non-conscious, super-intelligent entities to our planet. Recently, the implications of autonomous AI decision-making have led to calls from prominent leaders in the field for a moratorium on the development of AI, until a responsible form of control and regulation can be introduced.

But even if every country agreed to abide by strict rules and regulation, rogue organizations will be difficult to rein in.

The integration of autonomous AI in military defense systems has to be an area of particular concern. There is already evidence that humans will voluntarily relinquish significant power to increasingly capable systems, because they can carry out useful tasks much more rapidly and effectively without human intervention. Governments are therefore reluctant to regulate in this area given the strategic advantages AI offers, as has been recently and devastatingly demonstrated in Gaza.

This means we already edge dangerously close to a precipice where autonomous weapons operate beyond ethical boundaries and sidestep international law. In such a world, surrendering power to AI systems in order to gain a tactical advantage could inadvertently set off a chain of rapidly escalating, highly destructive events. In the blink of an eye, the collective intelligence of our planet could be obliterated.

Humanity is at a crucial point in its technological trajectory. Our actions now could determine whether we become an enduring interstellar civilization, or succumb to the challenges posed by our own creations.

Using SETI as a lens through which we can examine our future development adds a new dimension to the discussion on the future of AI. It is up to all of us to ensure that when we reach for the stars, we do so not as a cautionary tale for other civilizations, but as a beacon of hope – a species that learned to thrive alongside AI.

Originally published at The Conversation.

As the president of Messaging Extraterrestrial Intelligence, or METI, International, I helped design the message on Clipper with two fellow members of our board of directors: linguists Sheri Wells-Jensen and Laura Buszard-Welcher. METI International is a scientific organization dedicated to transmitting powerful radio messages to extraterrestrial life.

We collected audio recordings in 103 languages, and we decided how to convert these into waveforms that show these sounds visually. Colleagues from NASA etched these waveforms into the metal plate that shields the spacecraft’s sensitive electronics from Jupiter’s harsh radiation.

Related: Our solar system's ocean moons may be habitable — and their icy shells could hold proof

I also designed another part of the message that visually depicts the wavelengths of water’s constituents, because water is so important to the search for intelligent life in the universe.

Etching messages into spacecraft isn’t a new practice, and Clipper’s message fits into a decades-old tradition started by astronomer Carl Sagan.

In 1972 and 1973, two Pioneer spacecraft headed to Jupiter and Saturn carrying metal plaques engraved with scientific and pictorial messages. In 1977, two Voyager spacecraft headed to Jupiter, Saturn, Uranus and Nepture bearing gold-plated copper phonograph records. These records contained tutorials in mathematics and chemistry, as well as music, photos and sounds of Earth and greetings in 55 languages. 

Water words 

As water is essential for life on Earth, searching for its presence elsewhere has been key to many NASA missions. Astronomers suspect that Europa, where Clipper is headed, has an ocean underneath its icy surface, making it a prime candidate for the search for life in the outer solar system.

Part of the Clipper message features the word for water in 103 languages. We started with audio files collected online, but we then needed to analyze those and find an output that could be engraved on a metal plate. I ended up going back to some of the techniques I used in some of my early psycholinguistic research, where I explored how emotions are encoded in speech.

The 103 spoken words we recorded represent a global snapshot of the diversity of Earth’s languages. The outward-facing side of the Clipper plate shows the words as waveforms that track the varying intensity of sound as each word is spoken.

Each person whom we recorded saying the word “water” for the waveform had a connection to water. For example, the lawyer who contributed the word for water in Uzbek – “suv” – organizes an annual music festival in Uzbekistan to raise awareness of the desertification of the Aral Sea.

The native speaker of the Catalan water word – “aigua” – hunts for exoplanets, discovering potentially habitable planets that orbit other stars. 

Clipper’s message also pays homage to astronomer Frank Drake, the father of SETI – the Search for Extraterrestrial Intelligence – by bearing the Drake Equation, his namesake formula. By drawing on scientific data, as well as some best guess hunches, the Drake Equation estimates the number of extraterrestrial civilizations in the galaxy currently sending messages into the cosmos.

By one widely quoted estimate, there are a tenth as many of these extraterrestrial civilizations as one’s average lifetime in years. If civilizations survive for a million years, for example, there should be about 100,000 in the galaxy. If they last only a century on average, scientists would estimate that about 10 exist.

Radio astronomers study the universe by examining the radiation that chemical elements in space give off. They spend much of their time mapping the distribution of the most abundant chemical in the universe – hydrogen.

Hydrogen emits radiation at a certain frequency called the hydrogen line, which radio telescopes can detect. During Project Ozma, the first modern-day SETI experiment, Drake looked for artificial signals at the same frequency, because he figured scientists on other worlds might recognize hydrogen as universally significant and broadcast signals at that frequency.

The water hole 

As our team developed our water words message, I realized that the message would only make sense if it were discovered by someone already familiar with the contents inscribed on the plate. The Drake Equation would only make sense if someone already knew what each of the terms in the equation stood for.

The Europa Clipper will crash into Jupiter or one of its other moons, with Ganymede or Callisto the leading candidates. But if for some reason the mission changes and it survives that fate, then humans far in the future with a radically different cultural background and different language conventions may retrieve it millennia from now as an ancient artifact.

To ensure we had at least one part of the message that a distant future scientist might be able to understand, I also designed a pictorial representation of the same frequency that Drake used for Project Ozma: the hydrogen line. We engraved this on the Clipper plate, along with a frequency called the hydroxyl line.

When hydrogen (H+) and hydroxyl (OH-) combine, they form water. Scientists call the range of frequencies between these lines the “water hole.” The water hole represents the part of the radio spectrum where astronomers conducted the first SETI experiments.

We displayed the hydrogen and hydroxyl lines using their wavelengths in the Clipper message. The metal plate also has diagrams showing what hydrogen and hydroxyl look like at the atomic level.

We’re hoping that future chemists would recognize these chemical components as the ingredients of water. If they do, we will have succeeded in communicating at least a few core scientific concepts across time, space and language.

Waveforms let our team tie the messages on the two sides of the Clipper plate together. On the water words side, over a hundred words are depicted by their waveforms. On the other side, the wavelengths of hydrogen and hydroxyl – the constituents of water – are etched into the plate.

METI International funded the collection and curation of the water words, as well as my design of the hydrogen and hydroxyl lines, providing these to NASA at no cost.

While designing the message for the Europa Clipper, we got to reflect on the importance of water on Earth, and think about why astronomers feel so compelled to search for it beneath the icy crust of Jupiter’s moon Europa. The spacecraft is scheduled to enter Jupiter’s orbit in April 2030.

But spoiler alert: For the chief leader of the SETI Institute, established to search for and understand life beyond Earth, there's a need to step back and cuddle up to a cup of cosmic reality. 

"We don't have any evidence of any credible source that would indicate the presence of alien technology in our skies. And we never have," said Bill Diamond, president and chief executive officer of the SETI Institute, headquartered in Mountain View, California. "The idea that the government is keeping something like this secret is just totally absurd. There's no motivation to do so." 

Related: 'It's getting closer and closer for sure.' How SETI is expanding its search for alien intelligence (exclusive)

SETI is a key research contractor to NASA and the National Science Foundation, and collaborates with industry partners throughout Silicon Valley. Space.com caught up with Diamond for a close-encounter with his own thoughts and counterpoints to claims of alien visitation and to ask whether there's any signal in all the UFO noise.

Thought experiment 

Diamond said that, while we should not outright rule out the possibility that we might someday discover evidence of alien technology in our skies, "we should equally not jump to the conclusion that UFOs are alien technology in the absence of any compelling evidence to that effect. And there is no compelling evidence," he contends.

To help visualize why, Diamond urges people to try a thought experiment. 

The fastest spacecraft that humans have ever built and continues to head outward from Earth is NASA's New Horizons spacecraft. It was hurled outward back in January 2006, cruising by Pluto and is still adding mileage to its odometer.

"If you sent that spacecraft to our closest neighbor star, Alpha Centauri, it would take 80,000 years to get there," said Diamond. "Any civilization that has mastered the ability to traverse the incomprehensibly vast distances of interstellar space would have technology so far advanced from our own as to be beyond our comprehension."

It would be much like a smartphone to a Neanderthal, Diamond suggested. 

"If such beings exist, they would likely send hardware here first and not biology, and they certainly wouldn't crash-land in our deserts," he said, like the alleged and highly acclaimed 1947 nose-dive of a UFO and its accident-prone occupants near Roswell, New Mexico.

In short haul language, that's a long way to travel and run out of braking fluid.

Where's the mothership? 

"Long before they sent any craft into our sky they would have some understanding of what they were dealing with," Diamond observed, "as they would already know everything about our atmosphere, our airspace, our technology and more." 

It just wouldn't happen, Diamond emphasized.

"And if it did they wouldn't leave them behind. And by the way, if you have a small craft zipping around in our airspace, where is the mothership? And if they didn't want to be observed, they wouldn't be!"

Connective tissue 

All the same, in the public mind, is there some kind of connective tissue between SETI and UFOs?

"There is definitely connective tissue," Diamond responded. "Why do people have these beliefs? It is because they want to believe. Nobody really wants to think that this Earth is the only place in the vastness of space where life has emerged. Even that idea is also kind of absurd."

For example, Diamond points to the revelations cranked out by the NASA Kepler mission, lofted in March 2009. 

That hunter/data-gatherer spacecraft discovered more than 2,700 planets beyond our solar system. Compiling deep space data for nine years, the message from Kepler: there are billions of unseen planets, indeed, more planets than stars.

Statistical probability 

"Statistically speaking, every single star in the sky has one or more planets around it," Diamond pointed out. Furthermore, 50 percent or more of these are Earth-like (rocky surface and similar size) and in the habitable zone of their host star, he said.

"That implies the existence of tens of billions of potentially habitable worlds in our galaxy alone," Diamond said. "So indeed, the statistical probability that we are alone in the Universe is zero. Surely there is life beyond Earth!"  

But the presence, both in space and time, as well as proximity, of advanced alien civilizations is another matter completely, Diamond continued. "There are innumerable variables, all of which in the sciences of astrobiology, planetary science, astronomy and astrophysics, we are trying to figure out."

Accidental observations 

Diamond questions why any alien civilization would send biology when they could isntead send hardware. 

"The farthest things we have sent into space are hardware. And that's logical," said Diamond. "But if you did send beings and the most interesting thing you can do is draw circles in crops … come on!"

One other scoop of skepticism Diamond added is that every single UFO — now tied to the term Unidentified Anomalous Phenomena (UAP) — are all "accidental observations."

"Therefore, they are highly unreliable. They don't have instrumentation, technology, or methodology to discern what they are looking at," said Diamond.

Lastly, the SETI Institute leader said if the government actually believed in ET buzzing our planet, where's the study money? 

"The lack of government funding to study UAP/UFO is evidence of either the government being quite certain that there's nothing to these accidental observations — or — the government preferring that we not use available technology to closely watch our skies because of our own human technologies that are being developed — in secret," said Diamond.

"I think that's the most compelling bit of evidence against the idea that we've got visitors in our skies," Diamond concluded.

For more information on the SETI Institute and its programs, go to https://www.seti.org/ 

Netflix's new eight-episode alien invasion saga "3 Body Problem" uses the famous SETI (search for extraterrestrial intelligence) signal as a prominent plot device in its wild centuries-spanning narrative.

The Wow! signal was an intense narrowband radio signal detected on the night of Aug. 15, 1977 by Ohio State University's Big Ear Radio Observatory and the North American Astrophysical Observatory (NAAPO) during a standard SETI search. No personnel were on duty at the time, yet the strong 72-second-long signal was recorded by a computer printer.

Related: The search for alien life

It's so named for the exclamatory word boldly written in red on the computer printout sheet by its discoverer days later, OSU professor and astronomer Dr. Jerry Ehman, and remains perhaps the most promising SETI candidate ever received of a potential radio transmission from an extraterrestrial species. 

After 47 years and decades of dissection by researchers, the most recent work suggests that the Wow! signal might have come from the vicinity of a sun-like star situated 1,800 light-years away in the constellation Sagittarius. It's also been speculated that the signal came from a hydrogen cloud accompanying one of two comets, 266P/Christensen and P/2008 Y2 (Gibbs), which were passing through that exact section of the sky in 1977 when the Wow! signal was noticed.

"3 Body Problem," which drops on March 21, puts its own spin on the signal. In the series, Wow! is a real message from intelligent aliens beyond Earth. A Chinese astrophysicist in Inner Mongolia responds to the translated signal by inviting the aliens to visit Earth — to humanity's detriment, as we later learn.

In "3 Body Problem," the non-repeating communication is revealed to have been authenticated by one other radio telescope installation at China's Red Coast Base, yet covered up as a false alarm unique to the Ohio State University discovery.

But back to the real world: In 1977, the Big Ear was searching for any messages located at the electromagnetic frequency band of 1420.4056 megahertz, which is produced by the element hydrogen. 

"Since hydrogen is the most abundant element in the universe, there is good logic in guessing that an intelligent civilization within our Milky Way galaxy desirous of attracting attention to itself might broadcast a strong narrowband beacon signal at or near the frequency of the neutral hydrogen line," Ehman explained in a 30th anniversary report about the Wow! signal.

Whether the Wow! signal was the result of a broadcast from an alien civilization or simply a one-time natural cosmic event has never been determined. Multiple attempts to find it, or something like it, in the same patch of sky have come up empty over the decades.

So the enigmatic phenomenon adds an interesting layer to "3 Body Problem," introducing a new generation to the SETI mystery. 

"3 Body Problem" comes from "Game of Thrones" creators David Benioff and D.B. Weiss, along with "True Blood's" Alexander Woo." It's an adaptation of the first book in the "Remembrance of Earth's Past" novel trilogy by bestselling author Cixin Liu.

About 167,600 years ago, a blue supergiant star exploded as a supernova in the Large Magellanic Cloud, which is a small, satellite galaxy that neighbors our own Milky Way. Light emanating from that supernova raced through space at 299,792,458 meters per second (186,282 miles per second). 

Then, on 24 February 1987, it reached Earth. 

Related: Machine learning could help track down alien technology. Here's how

The supernova became known as SN 1987A, and its light did not stop at Earth. It  kept going, deeper and deeper into our galaxy where other alien life might catch a glimpse. This is where the concept of the SETI Ellipsoid comes from. It's defined as an elliptically shaped volume, with Earth at one foci and SN 1987A at the other; its perimeter indicates locations where there has been enough time for the supernova's light to reach a star, and for any technological life on a planet orbiting that star to send out a signal that would reach us now. 

The idea is that we can use the SETI ellipsoid as what's known as a Schelling point, a concept associated with game theory. It describes a kind of focal point  around which two protagonists — in this case, transmitting aliens and human astronomers watching or listening for their signals — can coordinate their activities without first communicating their intentions. If that sounds complicated, consider that SETI has been using Schelling points ever since Frank Drake's Project Ozma, the first-ever SETI search that occurred in April and May 1960. Drake had searched for radio signals at the iconic 21 centimeter hydrogen wavelength because he figured aliens would realize our astronomers routinely look at that wavelength. Transmitting on such a commonly used wavelength, he reasoned,  would increase the chance of a signal's detection.

"As Dr. Jill Tarter often points out, SETI searches are like looking for a needle in a 9-D haystack," said Sofia Sheikh of the SETI Institute and the University of California, Berkeley in a statement. "Any technique that can help us prioritize where to look, such as the SETI Ellipsoid, could potentially give us a shortcut to the most promising parts of the haystack."

The hope is that technological aliens who have seen SN 1987A would synchronize their signals with it, knowing that we would be looking for it on the SETI Ellipsoid. However, the problem has been that, until very recently, it has been impossible to search the ellipsoid with a reasonable degree of accuracy.

To understand why, let's take a look at some SETI and astronomical history. 

The concept of the SETI Ellipsoid is not new. It was first independently described by T. B. Tang in the Journal of the British Interplanetary Society in 1976, and by Soviet astronomer P. V. Makovetskii in 1977. At the time, there were no obvious targets around which to base a SETI Ellipsoid; Makovetskii proposed using Nova Cygni 1975, which was an outburst of a white dwarf accumulating matter from a companion red dwarf star, which prompted the system to brighten substantially for about a week.

After the discovery of SN 1987A, Hungarian astronomer Iván Almár realized it had created a new SETI Ellipsoid subject, and in 1994, Argentinian astronomer Guillermo Lemarchand described a search using that ellipsoid. But,  uncertainties in the distances of stars near the ellipsoid's perimeter were too great. Uncertainties in distance correspond to uncertainties in time; if we get the distance to a star wrong by even half a light year, for example, that means our search for synchronized signals would be six months too early or late. And timing may be everything with these technosignature hunts.

Only in the past ten years, with the advent of the European Space Agency's Gaia mission, meant to measure the positions and characteristics of a billion stars, have astronomers started gleaning distances to stars with the required accuracy to search SN 1987A's SETI ellipsoid. So, a team led by James Davenport of the University of Washington in Seattle combined the Gaia data with stars on the SETI Ellipsoid that are in the Continuous Viewing Zone of NASA's Transiting Exoplanet Survey Satellite (TESS).

TESS spends a year looking at each celestial hemisphere, and divides those hemispheres up into sectors. TESS gazes at each sector for 27 days, watching for exoplanetary transits, before moving on to the next sector. However, there's a region around each celestial pole that appears in every sector. This is the Continuous Viewing Zone — TESS gathers data from it for an entire year.

Davenport's team identified 32 stars in the Continuous Viewing Zone that are on the SETI Ellipsoid, and the year's worth of data allowed for some leeway in case of any lingering uncertainty in their distances. TESS, being an optical telescope, can only detect optical signals and not radio messages. Davenport's team studied the light of the 32 stars over the course of that year, looking for any anomalies that indicate a technological signature. These anomalies could include a brightening from a laser signal, an unorthodox transit from an artificial structure, or even an artificial outburst mimicking the light curve of SN 1987A. In 1994, Lemarchand suggested looking for a "fake pulsar" signal, as aliens might know that astronomers would be looking for a pulsar born in the fires of the supernova. (To date, no pulsar has been detected in SN 1987A.)

Suffice to say, Davenport's team found no anomalies and therefore no evidence of aliens was detected. However, the SETI Ellipsoid is always growing (at the speed of light, in fact) and it will move onto other stars in the future.

The upcoming PANOSETI (Panoramic SETI) project, which will continuously observe the entire sky visible from Lick Observatory in California and search for optical and near-infrared laser signals, will be perfect for probing the SETI Ellipsoid. The Vera C. Rubin Observatory in Chile could also be a game changer when it becomes operational later this decade.

"New surveys of the sky provide groundbreaking opportunities to search for technosignatures coordinated with supernovae," co-researcher Bárbara Cabrales of Smith College in the United States, said in the statement.

The analysis of the SETI Ellipsoid and the results from the stars in TESS' Continuous Viewing Zone were described last year in the The Astronomical Journal. 

Any "fishing expedition" for E.T. includes close-in studies of life in extreme environments right here on Earth, to help us recognize any signatures we might find on Mars or deep diving through the icy shell of Jupiter's moon, Europa. The search can also blend in the use of space-based telescopes to inspect Earth-like planets circling their home stars. Then there's cupping a proverbial ear to the cosmos using radio telescopes to pick up any bustling interstellar civilization or perhaps look for far-off laser-pulsed communiqués from extraterrestrial homebodies.

These and other efforts are actively pursued by the SETI Institute in Mountain View, California, right there in the high-tech heartbeat of Silicon Valley. More than a hundred institute scientists are busily carrying out research in astronomy and astrophysics, astrobiology, as well as exoplanets, climate and bio-geoscience and the Search for Extraterrestrial Intelligence (SETI).

Related: SETI scientists begin huge new hunt for intelligent aliens

Space.com caught up with Bill Diamond, President and CEO of the SETI Institute for an exclusive, mind-stretching close-encounter discussion regarding the mounting evidence for extraterrestrial intelligence. 

Spoiler alert! It's not that old tried, true and tired query "are we alone?" Rather, it's more like "just how crowded is it?"

Early stages

There's a lot going on today in terms of searching for and trying to understand potential extraterrestrial life in the universe, Diamond said.

"Much of the first several decades of SETI, the effort has been quite minimal, looking with fairly 'insensitive' instruments in fairly narrow parts of the radio spectrum in random parts of the sky. So hardly anything that could be considered a comprehensive endeavor," said Diamond.

But even today, in many ways, SETI work is still in the early stages. However, more and more is taking place with an increasing number of instruments and technologies around the world. "There's an extensive and expanded effort ongoing now," Diamond said.

COSMIC collaboration

For example, there's the Commensal Open-Source Multimode Interferometer Cluster Search for Extraterrestrial Intelligence — mercifully shortened to COSMIC SETI. 

All 27 antennas that constitute the Very Large Array (VLA) in New Mexico have been outfitted with new gear to perform 24/7 SETI observations under a collaboration between the SETI Institute and the National Radio Astronomy Observatory, the group that operates the VLA. 

Yes, that's the same VLA showcased in the 1997 sci-fi film "Contact," replete with actress Jodie Foster adorned with a tight-fitting stereo headset. In reality, the VLA was never used for SETI, Diamond noted, but now it is.

Detectable signatures

"COSMIC is really the most comprehensive SETI search on a single instrument in history. That's very exciting," Diamond said, and gives the COSMIC effort access to a complete and independent copy of the data streams from the entire VLA.

COSMIC will analyze data for the possible presence of "technosignatures" - detectable signatures and signals that shout out the presence of distant advanced civilizations. 

In scientific circles, technosignatures are viewed as a subset of the far more established search for "biosignatures" — evidence of microbial or other primitive life loitering on some of the billions of exoplanets we now know exist.

Newly augmented

"For classical radio SETI, there's more going on now around the world than there has ever been," Diamond said. That uptick also includes the SETI Institute's newly augmented Allen Telescope Array situated northeast of San Francisco. It was named after Paul Allen, co-founder of Microsoft, given his generous financial backing of the facility in its early phases.

The Allen Telescope Array (ATA) has undergone antenna redesign and now is outfitted with high-end computers, signal processors, and other electronics making it far faster than ever before, Diamond adds. "The instrument is performing at a level that it has never performed at since it was built. All of that is fairly new in the two to three years."

One output from ATA has been its use by SETI Institute scientists to delve into powerful Fast Radio Bursts (FRBs), a head-scratching phenomenon wanting of explanation. 

Philanthropic gift

A passionate booster in ATA's overhaul was Franklin Antonio, a co-founder of Qualcomm, a communications chip company. Antonio's support as an institute technical advisor continues with his philanthropic gift to the SETI Institute of $200 million after his passing last May.

That bequest is sparking an action plan that will enhance the institute's multi-disciplinary, multi-center research, education and outreach make-up, Diamond said.

Also on the institute's agenda is taking in and evaluating ideas from SETI researchers anywhere in the world to tap into a pool of money for such things as technology, software, or to run an experiment. 

"If we like what you're doing, we'll fund it," Diamond said. "We will kind of take the place of NASA for the time being as the only place in the world where you can submit a proposal to do SETI work."

Those three words

Roll back time to Columbus Day in 1992 when NASA initiated a formal, more intensive, SETI program. But less than a year later, Congress short-circuited the program. 

Is it time for the government to re-embrace the search for extraterrestrial intelligence?

"Yes, absolutely," Diamond responded. NASA, he said, has a trio of science questions it's spearheading: How does the Universe work? How did we get here?  Are we alone?

Almost every time NASA leadership publicly speaks, said Diamond, they invoke those three words — Are we alone?

"We all want to know. NASA clearly wants to know as it's one of their science priorities," Diamond said. "So isn't it time they get back in the business of trying to answer that question?"

Planets are everywhere

NASA's own Kepler space telescope served as the space agency's first planet-hunting mission. During nine years of deep space scoping, Diamond emphasized, it showed our galaxy contains billions of exoplanets. "It told us that planets are everywhere and a lot of them are potentially habitable."

NASA is starting to chip away at SETI work, Diamond noted. A NASA-funded grant to a SETI Institute scientist is using observations from the space agency's Transiting Exoplanet Survey Satellite (TESS). The intent is to purge out of the TESS data possible technosignatures aided by artificial intelligence/machine learning tools.

"So yes, I think the winds of change are blowing a little bit in favor of the government getting back into this business. And, in my opinion, I think they should step up and do it," Diamond said.

Neighborhood watch

With all the in-motion SETI research underway, just how prepared are we for a confirmed, door-ringing neighborhood watch revelation?

"The straight answer to that question is no, we are not necessarily ready, although it depends on what the answer is," Diamond responded. It's only a matter of time before this question is answered, he added, at one level or another. 

We should begin to think about how we convey this information, possible impacts to society, to religion, to politics, to technology, to governments, said Diamond. 

"I do think that with all these technologies, modalities, instruments looking in different ways," Diamond concluded, "it's getting closer and closer for sure."

Yes, I am being fully serious. It all begins with a fascinating paper entitled "Planet Hunters IX. KIC 8462852 – where's the flux?" 

In this paper, a crew of researchers presented their analysis of data gleaned from NASA's Kepler telescope. It concerned a star that resides about 1,470 light-years from where you're sitting named KIC 8462852, or Boyajian's Star in a nod to the study's lead author. According to the team's results, Boyajian's Star seemed to exhibit a bunch of very peculiar dips in light. 

Normally, when studying a star from our vantage point in the cosmos, telescopes can naturally see dips in starlight whenever something passes between them and the star itself. Imagine you're staring at a bright lightbulb, then someone passes in front of the lightbulb. Its emissions would appear interrupted. Usually, as you may expect, an exoplanet causes such dimming when orbiting its stellar host — but… not for Boyajian's Star. 

"It's not a sphere," Daniel Giles, a postdoctoral researcher at the SETI Institute said during the 243rd meeting of the American Astronomical Society in January. "It's composed of something like a bunch of panels … it looks like what a megastructure would look like." 

Because of this, following that 2015 result, the crowd went wild. News articles, follow-up observations, opinion pieces and even just general chatter started rippling through the astronomy niche. Okay, pause. I'll save you the trouble and let you know that the ultimate consensus was: No, these weird dips weren't caused by a massive piece of futuristic alien technology. "It's probably dust," Giles said. But here's the thing.

Related: 'Dyson sphere' legacy: Freeman Dyson's wild alien megastructure idea will live forever

"Signals like this were actually missed in the Kepler data," Giles explained. In fact, a huge reason the researchers behind the paper found the light dip anomaly at all was because citizen scientists spotted it by accident while searching for something else. 

Or as Giles puts it: "People weren't looking." 

So, that's precisely what he and fellow researchers aim to do. Perhaps, they believe, the truth about aliens lies straight in the data — we just have to look for it. But, like, really look.

Enlisting the machines 

In short, Giles and his team intend to search for the confusing, mysterious, intriguing and starkly out-of-the-ordinary signals in data collected by NASA's Transiting Exoplanet Survey Satellite, or TESS. They want to hunt for starlight dips that don't have a defined shape, a defined depth or even a defined timeframe. The cosmic outliers. 

Strange dips like these can be spotted through photometric curves, which represent brightness over time. "We're counting photons," Giles explained in a nutshell. The kicker, however, is precisely how the team wishes to embark on this anomaly-hunting quest: Machine learning. 

The process is pretty much as follows.

TESS data used in the study is based on the satellite's view of different sky sectors. These sectors were viewed across some 30 days at a time; during that scan, TESS took a snapshot of the observed area once every 30 minutes. This eventually led the team to about 60 million light curves ready for analysis, generated for stars brighter than 14 magnitude. In the magnitude system, smaller numbers are brighter than larger numbers — a magnitude 0 object is 100 times brighter than a magnitude 5 object, for instance. A full moon goes into the negatives with a magnitude of around -12.6; the sun shines around magnitude -27. And so on.

The next step is to start mass organizing the light curves based on things like their shapes and periodicities. "We're processing 60 million different light curves so we need them to be cheap and easy to calculate," Giles said. "We calculate these cheap metrics and then we run the anomaly detection on it, and this is a density based anomaly detection — we find out what has features that stick out." 

Then, after culling the data down to a manageable size, the team gets ready to apply more granular techniques that typically take more computational power. The nitty gritty, difficult-to-do analyses. "We ensure that the behavior actually exists, and is astrophysical and not due to an instrumentation issue," Giles said. 

If something exhibits a recognizable pattern, well, time to go back to the culling stage.

"Finally, we go through manually," Giles said, "because nothing is better at finding weird stuff than the human eye."

To find an alien, you might need a human 

To be perfectly honest, I was thrilled to hear something intrinsically human can find strange things like no machine really can. I think it grounds our admittedly wild endeavor of trying to locate intelligent aliens. We're inherently curious I suppose, and somehow drawn to lapses in patterns. 

"There's a certain level to which we can use ML methods," Giles told Space.com, "but ultimately, we need to be able to understand why it is things are happening."

Maybe a pool full of even the most highly accurate datasets is just that  —  a pool full of highly accurate datasets  —  until a human starts parsing through to make connections a machine hasn't yet been programmed to recognize. 

"For things like anomaly detection, there's an additional trick," Giles said. "There's not a ground truth, so we can't train something necessarily to find the weirdest stuff, or the stuff that's the most interesting, because we don't necessarily know what that's going to be."

Even when it comes to standard robotics that aim to mimic human structure, a limiting step for scientists is with regard to decoding physical laws that dictate the way we move. It's because, as humans, we don't really need to know how some aspects of humanity work. They just work. A few years ago, for instance, one team made a breakthrough in figuring out how our fingerprints impact our grip. You know how when you wash slippery dishes, you instinctively know how hard to hold the dishes so they don't fall out of your hands? You're unconsciously considering your fingerprints during that whole thing. But scientists literally had to make a new law of physics to convert that instinct into written fact.

There seems to be a similar concern for ML — and artificial intelligence, for that matter — even though the two are technically trainable to come up with some solutions of their own. It's tough to program a machine to find something that we haven't found before, because what would we tell it to look for? It's sort of like how scientists champion the James Webb Space Telescope as the invention that might answer some cosmic questions we never thought to ask. 

"There are limits to what AI and ML can do for us, but there are also a lot of opportunities as long as we understand what ML is doing specifically," Giles said.

Food for thought.

However, Giles says the team is also trying to search for specific anomalies that are indeed codable. "We have injected nearly 2 million different artificial signals into light curves that don't have any dip signatures we know about, but still have artifacts in them so they still have behavior going on," he said.

As for the anomaly results so far? "None of these so far speak to us like they're megastructures, 

"But they are certainly interesting."

Biologists, anthropologists, linguists and other experts specializing in language and communication have begun to explore what non-human, off-Earth language might look like. 

Arguably, such thinking sparks thought about the fabricated Klingon language, the cosmic "Klingonese" chatter spoken by one the alien species on "Star Trek." There's even a thriving Klingon Language Institute, which was founded in 1992.

But you can put sci-fi aside, for scientists in the real world are investigating the possible forms that alien languages might take — and whether we might be able to understand them.

Related: The search for alien life

Off-Earth intelligence

Astrobiologist Douglas Vakoch is president of Messaging Extraterrestrial Intelligence (METI International) in San Francisco. He's co-editor with Jeffrey Punske of a new volume, "Xenolinguistics: Towards a Science of Extraterrestrial Language" (Routledge Taylor & Francis Group (2023).

The book is anchored in what is known about human language and animal communication systems, but it offers suggestions about what we may find if we encounter non-Earth intelligence.

For over six decades, researchers have been engaged in the search for extraterrestrial Intelligence (SETI), listening for signals with radio telescopes — and they could succeed tomorrow, Vakoch told Space.com. (METI, as its name suggests, concerns the possibility of communicating with alien intelligence — making meaningful contact.)

"We might be faced with understanding a message from an unknown civilization, and linguists could provide the key to cracking the code," said Vakoch. "The recommendations coming out of our new book are directly shaping how we will say 'Hello, universe.'"

Vakoch highlighted the importance of communicating our intentions as the hallmark and rationale for METI messages. "Another key question is whether universal grammar of the sort we see across languages on Earth will also hold true more broadly in the universe," he says.

As noted in the volume, one major point is that communication involves more than getting across the content of your message. "You also want to communicate your intention," said Vakoch.

Related: If aliens have visited the solar system, here's how to find clues they left

Start a conversation

One of the common objections to METI, Vakoch pointed out, is that we may alert hostile extraterrestrials to our existence and provoke an alien invasion. 

"In reality, any civilization with the capacity to travel between the stars also has the technology to pick up the accidental radio and television signals that have been leaking off into space for the past century," Vakoch said. 

So any aliens picking up our targeted messages won't be surprised to know we exist, Vakoch added. "But what will surprise them is that we're attempting to start a conversation. That's the whole point of METI — to get across our intention of making first contact."

Universal principles

Vakoch said that the aliens he is most interested in are the ones we can make contact with. 

"Those are the aliens who have developed the technology to transmit and receive radio signals. In the past, when scientists have sent interstellar messages, this shared technology has provided the foundation for crafting the messages." 

The messages we've sent into space so far have relied on possibly universal principles of math and science as a starting point, said Vakoch. "But maybe there's something more basic. Long before humans had math and science, we had language. Maybe the same is true on planets orbiting other stars."

In the end, Vakoch thinks, the idea that we must choose between either math and science, on one hand, or language, on the other, is itself too simplistic.

Core of language

Co-editor of the new xenolinguistics book is Jeffrey Punske, an associate professor and the director of undergraduate studies in linguistics at Southern Illinois University in Carbondale. 

What we define as the core of language may be fundamentally constrained by external considerations. If so, then it is almost certain that a linguistic, non-human intelligence would have the same core of language, Punske suggests. 

"However, there are many aspects of language that are universal to human language that cannot solely be attributed to such externals," he said. "Those aspects are likely products of the structure of human cognition. There is certainly no guarantee that a non-human intelligence would share our cognitive systems. Thus, while the underlying structure of language might be the same, the message might not be interpretable."

New perspective

Excited that scientists are beginning to think seriously about xenolinguistics is Bridget Samuels of the University of Southern California (USC). 

Samuels is conducting research in two areas that address where universal grammar may fit in the universe: How did language arise in our species, and what are the limits of variation in human language? 

"The study of animal communication has exploded in recent years, and it's given us a new perspective on how human language is, and isn't, unique," Samuels, the project director at USC's Center for Craniofacial Molecular Biology, told Space.com. "Also, how communication systems are shaped by the unique cognitive abilities of the organisms that use them, as well as by the environmental niches they inhabit." 

Invariant laws of physics

Those lines of inquiry, combined with a "third factor" in language design — factors that shape language beyond our genetic endowment and experience — have set the stage for theorizing in entirely new ways about universal grammar, Samuels said.

That theorizing has helped Samuels shape and share a prediction with Punske: "Some aspects of language syntax and externalization may even be shared by extraterrestrial languages, as they are constrained by invariant laws of physics."

By pondering language and animal communication in a cosmic context, Vakoch said, we are forced to rethink just how unique language is, even on our own planet — whether or not we ever make contact with extraterrestrials. 

"Xenolinguistics shows that human language may not have the privileged position we've always assumed," he said.

The new project is called COSMIC ("Commensal Open-Source Multimode Interferometer Cluster") and is in operation at the Karl G. Jansky Very Large Array (VLA) of radio telescopes in New Mexico. The VLA was featured in Robert Zemeckis' 1997 movie "Contact," starring Jodie Foster and based on Carl Sagan's famous novel of the same name.

COSMIC makes this possible and delivers a huge jump in coverage. Whereas previous SETI surveys have only been able to scrutinize a few thousand stars, COSMIC on the VLA will listen in on hundreds of thousands, and potentially millions, of star systems at frequencies between 0.75 and 50 GHz. It will enable a detailed SETI search of 80% of the entire sky (from declinations of -40 degrees to the zenith), which is orders of magnitude more in depth than all previous SETI searches combined.

Related: The search for alien life

"Currently the focus is on creating one of the largest surveys for technological signals, with over 500,000 sources observed in the first six months," said COSMIC project scientist Chenoa Tremblay, an astronomer at the SETI Institute, in a press statement. Currently, COSMIC is scanning cosmic radio sources at a rate of about 2,000 per hour.

COSMIC is able to piggyback on the VLA Sky Survey (VLASS), which commenced its third observing run back in January 2023. COSMIC receives a copy of the raw data collected by the 27-dish radio array, before the VLA does any automated, standard processing to it. This allows SETI scientists to process the data however they want to, and in real time, too. 

This rapid analysis is crucial. Often, SETI searches have detected interesting narrowband signals, but they are not noticed until weeks or months later when the data is analyzed. Often, when astronomers go for a second look, the signal has vanished, so there's no way to know if it was a real E.T. signal or, more likely, radio frequency interference (RFI) from human activities on (or in orbit around) Earth. Bona fide ET signals could be brief bursts and require quick identification and follow up.

Speaking of rapid signals, COSMIC has extremely high time sensitivity; it's able to detect radio signals as short as nanoseconds. Again, this is an important ability to have. Transmitting across interstellar distances is not cheap: in terms of power output, the energy resources required to maintain an omnidirectional transmission across hours, days, months or years that can be detected dozens or even hundreds or thousands of light-years away is immense. More cost-effective would be for aliens to beam nanosecond pulses that hit Earth for a short time before moving on to other planetary systems, and then cycle back to Earth. Many previous SETI radio searches, however, have not had integration times short enough to detect these nanosecond, or even millisecond, pulses.

The COSMIC system has also been designed with the future in mind, by leaving room for upgrades that can keep it at the peak of SETI experimentation. For example, the number of targets that can be simultaneously observed could be increased, and machine-learning algorithms introduced to analyze the data even more assiduously. 

Related: SETI & the search for extraterrestrial life

Machine-learning experiments have previously been conducted on SETI data gathered by the 330-foot (100 meters) Robert C. Byrd radio telescope at the Green Bank Observatory in West Virginia. Currently, however, the data analysis is being conducted manually using statistical techniques while scientists better familiarize themselves with how the system collects and presents data. Once they are confident that they fully understand the system, they can unleash machine learning onto it.

The system is also adaptable, and can be used for astronomical projects beyond SETI.

"The flexibility of the design allows for a wide range of other scientific opportunities, such as studying fast-radio burst pulse structures and searching for axion dark matter candidates," said Tremblay.

To enable this, COSMIC and the VLA are utilizing an ethernet-based system that will allow other experiments to simply plug in and use COSMIC's processing power. This ethernet technology is already in use at several radio telescopes, including MeerKAT (which is also conducting its own SETI experiment) in South Africa and the Murchison Wide-field Array in Australia.

As a test of the COSMIC system, Tremblay's team listened in on a data downlink at 8.4GHz from NASA's Voyager 1 spacecraft, which is currently located about 159 astronomical units (14.8 billion miles, or 23.8 billion kilometers) from Earth.

Now, with about half a million radio sources already in the database and analyzed, the biggest-ever search for aliens is beginning in earnest.

Details of the first six months of the COSMIC project are described in a new paper, with Tremblay as lead author, published on Dec. 27 in The Astronomical Journal.

This was the message that a group of Kentucky scientists, linguists and scholars recently beamed at the TRAPPIST-1 system, which lies 40 light-years from Earth and harbors multiple potentially habitable planets.

The missive represented the very first interstellar travel advertisement, according to VisitLEX, the group behind the effort.

Related: The search for alien life

VisitLEX's tourism team at the Lexington Convention and Visitors Bureau partnered with the Cornett ad agency to devise a playful campaign with sci-fi flavor. The team used a modified infrared laser to deliver a specially coded message, which was approved by the U.S. Federal Aviation Administration. 

Here are details from the VisitLEX press release:

"When the message reaches its destination in 2063, TRAPPIST-1 inhabitants will find a coded bitmap image with clues as to its origin and intent of the transmission. They'll also see bucolic photos of the Horse Capital of the World, noting the wide-open spaces perfect for landing a spacecraft. They'll learn why Lexington has the best food, bourbon and music on Earth — getting a taste via an audio recording from legendary blues musician Tee Dee Young."

If E.T. does eventually receive the message and pack their bags for our solar system, eager to take in The Bluegrass State's hospitality, thoroughbred race horses and bourbon industry, they'll have to cover 235 trillion miles (378 trillion kilometers) to get here. That's a bit of a trip, but who knows how fast their craft can go?

"We are targeting the TRAPPIST-1 system because we might actually get an answer in somebody's lifetime if there's somebody there watching," said astrobiologist and SETI (search for extraterrestrial intelligence) scientist Robert Lodder. "But the reason scientists have been interested in it lately is because of the large number of planets it has in what is considered to be the habitable zone. So, there could be life there. Why not send a signal and see if they answer?"

This message was sent last month from Lexington's Kentucky Horse Park museum and event center, during a festive evening ceremony that drew a sign-waving crowd. 

"The bitmap image is the key to it all. We included imagery representing the elements of life, our iconic Lexington rolling hills and the molecular structure for water, bourbon and even dopamine … because Lexington is fun!" added linguistics expert Andrew Byrd.

First of all, the consequences of first contact strongly depend on the way it takes place. The paper offers the view that first contact with alien life poses considerable risks for humanity. Additionally, a first contact event could also take place without being culturally recognized.

The intriguing new research paper is led by Andreas Anton of the Institute for Frontier Areas of Psychology and Mental Health in Freiburg, Germany.

Related: The search for alien life

Scenarios

Anton and colleagues serve up a set of scenarios:

• The signal scenario is the basis of SETI (search for extraterrestrial intelligence) programs, in which radio astronomers search for signs of alien civilizations. It assumes that radio telescopes can pick up artificial signals from the far reaches of space.
• The technosignature scenario envisions that future powerful telescopes will find evidence of past or present extraterrestrial technology.
• The artifact scenario assumes that one day, somewhere in our solar system (or even on Earth itself), we will come across the material remains — such as a space probe — of an extraterrestrial civilization.
• The encounter scenario involves the appearance of an alien spacecraft in near-Earth space that can be assumed, based on its flight maneuvers or other actions, to be controlled by intelligence, either biological or artificial.

Biological beings or artificial intelligence?

The prospect of an encounter scenario, the paper points out, raises an important question: Whether the alien technology is controlled by a biological life form or an artificial intelligence.

"A biological life form, we suspect, could potentially cause greater anxiety, as the immediate question would be what 'they' want here. It also has an inbuilt assumption that they have a relatively nearby base or have superfast travel (maybe faster than light) and would thus be very far ahead of us technologically," Anton and co-authors write in their paper. 

"However, the question of whether the encounter is with a biological life form or the emissaries of a machine civilization could remain unresolved for a long time," they add.

Be prepared

The paper concludes by acknowledging that the more we know about the universe and the further we penetrate into the cosmos through our own research activities, "the more likely it is that we will be confronted with alien civilizations, their signals or their legacies."

That being the case, the researchers suggest, humanity needs to be prepared as a global society for this scenario.

"In the political sphere, the question of how to deal with this discovery and possible communication with extraterrestrial civilizations would lead to a global discourse," they write in the paper. "International cooperation would be essential to develop a unified approach to dealing with this new reality."

 This research paper, titled "Meeting extraterrestrials: Scenarios of first contact from the perspective of exosociology," is available here. 

Researchers from the SETI Institute, University of California Davis and the Alaska Whale Foundation recently "conversed" with a humpback whale named Twain using an underwater speaker and recorded a humpback "contact" call. Twain responded to the researchers' call by matching the interval variations between signals of each playback call over a 20-minute period. 

If you're having a Star Trek flashback, yes, this is awfully reminiscent of that one film in which the crew receives alien whale transmissions that can only be decoded underwater. And in fact, mirroring our sci-fi fantasies, this demonstration of interspecies communication has implications for the search for extraterrestrial intelligence, according to a statement from the SETI Institute. 

"We believe this is the first such communicative exchange between humans and humpback whales in the humpback ‘language,'" Brenda McCowan, lead author of the study from U.C. Davis, said in the statement. 

Related: Why are we still searching for intelligent alien life?

Much like how astronaut crews simulate missions to Mars or the moon on Earth, the Whale-SETI team is studying humpback whale communication systems to better understand how to detect and interpret signals from outer space. Their findings can be used to develop filters that can be applied to any extraterrestrial signals received, according to the statement. 

"Because of current limitations on technology, an important assumption of the search for extraterrestrial intelligence is that extraterrestrials will be interested in making contact and so target human receivers," Laurance Doyle, coauthor of the study from the SETI Institute, said in the statement. "This important assumption is certainly supported by the behavior of humpback whales."

Twain's response to each playback call showcases a sophisticated level of understanding and interaction. The humpback whale approached and circled the team’s boat upon hearing the contact call played via an underwater speaker. Matching the interval variations between each call mirrors a human-like conversational style, according to the study. 

"Humpback whales are extremely intelligent, have complex social systems, make tools — nets out of bubbles to catch fish — and communicate extensively with both songs and social calls," Fred Sharpe, co-author of the study from the Alaska Whale Foundation, said in the statement. 

Therefore, working with humpback whales offers a unique opportunity to study intelligent communication in non-human species. The team will apply principles of information theory to develop filters that can aid in processing extraterrestrial signals and the search for intelligent life beyond Earth.

Their findings were published Nov. 29 in the journal PeerJ.

The Search for Extraterrestrial Intelligence (Seti) constitutes a branch of astronomy dedicated to finding extraterrestrial life by searching for unusual signals, dubbed technosignatures. The identification of a technosignature wouldn’t just signify the existence of life, but specifically point to the presence of intelligent life using advanced technology.

That said, 60 years of searches have so far come up short. But now my colleagues at Breakthrough Listen and I have started investigating a previously unexplored range of frequencies.

Seti makes the assumption that extraterrestrial civilisations might rely on technology in a similar way to people on Earth, such as using cell phones, satellites or radar.

Related: The search for extraterrestrial intelligence gets a new home at Oxford

Since a significant portion of such technology generates signals that are prominently detectable in radio frequencies, focusing on these wavelengths serves as a logical starting point in the quest for potential extraterrestrial intelligence.

Previous technosignature surveys have included only the radio frequency band above 600 MHz, leaving lower frequencies virtually unexplored. That’s despite the fact that everyday communication services such as air traffic control, marine emergency broadcasting and FM radio stations all emit this type of low-frequency radiation on Earth.

The reason it hasn’t been explored is that telescopes that operate at these frequencies are rather new. And lower-frequency radio waves have less energy, meaning they can be more challenging to detect.

In our concluded survey, we ventured into these frequencies for the first time ever.

The Low Frequency Array (Lofar) is the world’s most sensitive low-frequency telescope, operating from 10-250 MHz. It’s composed of 52 radio telescopes with more on the way, spread across Europe. These telescopes can reach a high resolution when used in unison.

Our survey, however, only made use of two of these stations: one situated in Birr, Ireland, and the other in Onsala, Sweden. We surveyed 44 planets orbiting other stars than our Sun that had been identified by Nasa’s Transiting Exoplanet Survey Satellite. Over the course of two summers, we scanned these planets at 110 to 190 MHz with our two telescopes.

Initially, this doesn’t seem like a large amount of targets, but low-frequency observation boasts a major advantage in having large fields of view compared with their higher-frequency siblings. That’s because the area of the sky covered decreases with higher frequencies.

In the case of Lofar, we covered 5.27 square degrees of the sky for each pointing of our telescopes. This culminated in 36,000 targets per telescope pointing – or more than 1,600,000 targets in total, when you check what other stars are nearby and include their planets as well.

Interfering signals

Searching for technosignatures from space introduces a significant challenge — the same technosignatures are ubiquitous on Earth. This presents an obstacle as the telescopes in these searches boast sensitivity levels that can detect signals, such as a phone call, from halfway across the solar system.

Consequently, the data collected is inundated with thousands of signals originating from Earth, posing a considerable difficulty in isolating and identifying signals that could be of extraterrestrial origin. The need to sift through this extensive and noisy dataset adds a layer of complexity to the search.

We came up with an innovative approach to mitigating such radio frequency interference, called the “coincidence rejection” method. This takes into account the local radio emissions at each of our telescopes. For example, if I am using the telephone close to the telescope in Ireland to call my supervisor, that same call won’t appear in the data in Sweden, and vice versa (mainly because the telescope isn’t pointing in our direction, it’s pointing at an exoplanet candidate).

So, we decided to only include signatures in the dataset if they exhibited a simultaneous presence at both stations, suggesting they come from outside Earth.

In this way, we whittled down thousands of candidate signals to zero. This means we didn’t find any signs of intelligent life with our search, but we have only just started – and there are likely to be an enormous number of Earth-like planets out there. Knowing that the coincidence rejection method works with a high success rate may be key to helping us discover life at one of these planets in the future.

There are many ways forward for technosignature searches at low frequencies. Currently, there is a sister survey (Nenufar) being carried out on that operates at 30-85 MHz. Along with this, further Lofar observations will increase the volume of the survey by a factor of ten over the course of the coming year. The collected data is also used for investigating astronomical objects known as pulsars, fast radio bursts, radio exoplanets and more.

Thankfully, we’re only at the start of a long journey. I have no doubt that many wondrous things will be found. And if we’re lucky, we may reap the biggest reward of all: some company in the cosmos.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Thus, a new philanthropic gift for the SETI Institute, to the tune of 200 million dollars, will ensure the SETI Institute's efforts will continue long into the future, giving astronomers the best chance of answering one of the most intriguing scientific and philosophical questions our species grapples with — are we alone? 

The large sum was donated by the estate of the late tech entrepreneur and co-founder of Qualcomm, Franklin Antonnio. Antonnio spent 12 years working with SETI before he passed away on May 13th, 2022. 

Related: 'Alien' signal beamed to Earth from Mars in SETI test

"Not only was Franklin the primary benefactor of SETI research at the Allen Telescope Array (ATA), but he was an integral part of the technical team. His extraordinary knowledge of communications technology was invaluable in upgrading the ATA to the world-class radio telescope instrument it is today," Andrew Siemion, director of SETI Research at the University of Oxford, said in a statement.

The SETI Institute, founded in 1984,  is a non-profit, multidisciplinary research and education organization that employs over 100 scientists across 173 separate programs. Research grants form the bulk of SETI's federal funding, yet most projects the Institute carries out are dependent on philanthropic and private funding. SETI has an annual operating budget that usually falls between 25 and 30 million, which means the gift will quite greatly ensure the continued operations of the Institute for years to come. 

The additional funding will also allow SETI to consolidate current projects which have sought to harness the power of data analytics, machine learning and advanced signal detection technologies in their efforts to identify intelligent technology elsewhere in the universe. 

"This gift will impact all research domains of the SETI Institute," Nathalie Cabrol, director of the Carl Sagan Center for Research, said in the statement.

"It will provide our teams the freedom to pursue their own science priorities, and to examine the technological, philosophical and societal impact of their research on our daily lives here on Earth," she added. 

Increasingly, researchers working in astronomy and astrobiology are taking seriously the idea that our first unambiguous detection of life elsewhere in the cosmos could come in the form of a technosignature — evidence that points to the use of alien technology.  

SETI, the search for extraterrestrial intelligence, has traditionally focused on radio frequencies higher than a gigahertz, such as the hydrogen-line frequency at 1.42 GHz. SETI astronomers tend to shy away from lower frequencies because Earth's atmosphere renders observations noisy.

However, Europe's Low Frequency Array, or LOFAR for short, is specially designed to conduct radio astronomy at these very frequencies. 

Related: The search for alien life (reference) 

LOFAR is an array of radio antennas that span hundreds of kilometers across Europe, centered in the Netherlands but with additional stations in France, Germany, Ireland, Latvia, Poland, Sweden and the United Kingdom. The stations incorporate two types of antenna: low band antennas that operate between 10 and 90 MHz, and high band antennas that listen to the universe between 100 and 250 MHz.

In conjunction with the Breakthrough Listen SETI project, the LOFAR stations in Ireland and Sweden have been used in conjunction with one another in the first part of Breakthrough Listen's first-ever low-frequency search.

This search used the high band antennas to listen for radio signals at frequencies of between 110 and 190 MHz. Primarily, the search is looking for leakage from high-power transmitters, such as planetary radar or communications with spacecraft. The search encompassed 1,631,198 target star systems identified by NASA's Transiting Exoplanet Survey Satellite (TESS) and the European Space Agency's Gaia astrometric probe.

By using multiple sites in Ireland and Sweden, astronomers were able to negate the effects of radio-frequency interference and quickly rule out any false positives. For example, if an anomalous signal were only spotted by one station and not the others, it would be local interference. Only a signal coming from space could be detected by all the stations.

No narrowband radio signals with a distinctive frequency drift caused by the orbital motion of an exoplanet hosting a transmitter beaming out signals with a power of at least tens of millions of watts were detected. However, the low-frequency search is only just beginning, and improvements in coming years will increase its sensitivity. 

"LOFAR is soon to undergo a staged series of upgrades across all stations in the array across Europe, which will allow an even broader SETI at ranges of 15-240MHz," said graduate student Owen Johnson of Trinity College Dublin, who is the lead author of a new paper describing the results, in a statement. 

Among these upgrades will be two new LOFAR stations in Bulgaria and Italy. Computing software and artificial-intelligence algorithms will also speed up the analysis of the results.

"We have billions of star systems to explore and will be relying on some machine-learning techniques to sift through the immense volume of data," said Johnson. "That in itself is interesting — it would be fairly ironic if humankind discovered alien life by using artificial intelligence." 

The first results from the LOFAR SETI search were published on Oct. 24 in The Astronomical Journal.

SETI, which stands for the Search for Extraterrestrial Intelligence, received a huge boost in 2015 with the launch of Breakthrough Listen. This $100-million-dollar private venture by the Breakthrough Initiatives foundation focuses on searching for technosignatures, signals from or indications of technologically-advanced extraterrestrial species. 

Breakthrough Listen has previously been headquartered at the University of California, Berkeley, but the new international headquarters at the Department of Physics at Oxford will take better advantage of the Square Kilometer Array (SKA), which is a huge array of radio dishes and antennas in South Africa and Australia. 

The SKA should be operational by around 2030. It will transform radio astronomy, observing the radio sky with 50 times the sensitivity of other radio-telescope arrays, and will be capable of surveying the sky 10,000 times faster. Physicists at Oxford have played a leading role in building hardware and writing software for the SKA, and will be able to tailor specific instrumentation for SETI. 

Related: At a powerful radio telescope, the hunt for signals from intelligent extraterrestrial life is on

Joining the team at Oxford will Andrew Siemion of the University of California, Berkeley, who has been Breakthrough Listen's Principal Investigator since its inception. "We are delighted to launch a new era of Listen here at Oxford," concluded Breakthrough's Executive Director, Peter Worden. "This collaboration will be a tremendous fusion of knowledge, resources, and passion to understand our place in the cosmos."

"This is an extraordinarily exciting partnership, bringing a large-scale SETI program to the UK," said Rob Fender, who is Oxford's Head of Astrophysics, in a statement. "This move recognizes how the University of Oxford's existing astrophysics programs in radio astronomy instrumentation, astrophysical transients and exoplanetary studies make it the perfect base for Breakthrough Listen."

The timing coincides with Breakthrough Listen's other new partnership with South Africa's MeerKAT array of 64 radio antennas, which has been a technological precursor for the SKA. MeerKAT began listening to a million stars for extraterrestrial radio signals in December 2022.

Breakthrough Listen, like most SETI projects, focuses on searching for radio signals, but it also encompasses technosignatures in general. These are defined as evidence for the activity of technological extraterrestrial species, but SETI astronomers deliberately keep the definition open-ended so as not to allow human biases to rule anything out. For example, one area in which astronomers search for technosignatures is in anomalous astrophysical transients — bursts of energy or light with no obvious explanation, which could potentially originate from extraterrestrial engineering on scales vastly greater than we can conceive. 

Breakthrough Listen scientists will search for anomalous astrophysical transients in data collected as part of the Legacy Survey of Space and Time (LSST) that will be conducted by the Vera C. Rubin Observatory in Chile when it becomes operational in 2024.

Breakthrough Listen also searches for possible "megastructures," giant non-natural objects, in transits detected by the likes of NASA's Transiting Exoplanet Survey Satellite (TESS), with the best example being Tabby's Star, which was revealed in 2015 to be experiencing irregular and very deep dimming events caused by unknown objects passing in front of it and dimming its light. It was later revealed that the objects were huge clouds of dust, but any real megastructures orbiting a star would result in similar transit events.

In particular, the Oxford group will place emphasis on the search for life on the nearest exoplanets. And all of the above will be done by developing new cutting-edge machine-learning algorithms that can analyze large amounts of data faster and in greater detail than more traditional methods.

Already, astronomers have used machine learning to detect eight possible SETI signals in data from the Green Bank radio telescope in West Virginia.

Looking a little further ahead, proposals for a lunar far side radio telescope to be used for SETI will also be developed by scientists at Oxford. The far side of the moon is a radio-quiet area, shielded from all the radio frequency interference put out by human activity on Earth, meaning it can obtain an unprecedented sensitivity for listening for faint radio signals.

An increasing number of scientists suspect that if we ever do make contact with alien life, we will be communicating with a computer.

This thinking revolves around an event called the singularity. This term, borrowed from mathematics, signifies a point where our knowledge of math and physics breaks down and we can no longer accurately characterize what we're trying to describe. A black hole singularity is a good example of this.

Related: Could AI find alien life faster than humans, and would it tell us?

In computer science and technology, the singularity describes the moment when artificial intelligence develops so fast that it results in a superintelligence — an artificial general intelligence, as opposed to the very specific machine-learning algorithms we have today — that experiences runaway growth in computing power and intellectual ability. This superintelligence would grow so far ahead of us, so quickly, that we would lose the ability to understand or explain it. 

Computer scientists have been speculating that the singularity could come soon; most predictions seem to agree on the period between 2030 and 2045. What happens beyond the singularity is anyone's guess.

There's no guarantee that the singularity will come to pass; many academics remain skeptical. However, if it does, the timescales would be remarkable, given that it is predicted to occur just 250 years after the Industrial Revolution, 130 to 140 years after the Wright brothers' first powered flight, a century after the atom was first split and 50 years after the invention of the World Wide Web. If we are a typical civilization in the galaxy, the singularity would seem to happen early in the life of a technological species.

Now, consider the age of the universe: 13.8 billion years. Assuming that life has been able, in theory, to develop and evolve for the vast majority of that history, alien species could be billions of years older than our solar system and many billions of years older than Homo sapiens. They would have had plenty of time to pass through the technological singularity, which is why so many researchers studying the search for extraterrestrial intelligence (SETI) are convinced that technological aliens will be artificial intelligences.

"This is very much at the vanguard of thinking in some sections of the SETI community," Eamonn Kerins, an astrophysicist and SETI researcher at the Jodrell Bank Centre for Astrophysics at the University of Manchester in the U.K., told Space.com. "We ourselves are very close to realizing artificial general intelligence (AGI), and there's an expectation that once you reach that point, it can then accelerate away at a very fast rate and quickly outstrip ourselves in intelligence."

Searching for superintelligences 

Suppose alien life was some form of superintelligence that had gone way past the singularity. What would it mean for SETI?

SETI focuses on searching for radio signals, the same kind that humans transmit. There are still very good reasons for searching the radio spectrum: Radio waves can permeate the Milky Way galaxy, they're a relatively simple means of signaling, and aliens would suspect that our astronomers were already studying the universe in radio waves and would therefore be more likely to spot a radio signal. 

A superintelligence billions of years older than us, however, might have long since moved past radio and might not even care enough to attempt to contact primitive life-forms on Earth.

Beyond looking for signals, recent SETI efforts have been considering the broader concept of technosignatures — evidence for extraterrestrial technology or engineering — possibly on an enormous scale for it to be noticeable to us. This might be one way of detecting an artificial superintelligence since the search for technosignatures is agnostic about why the aliens are doing what they're doing. Beyond the singularity, such reasons might be difficult for us to discern.

"Some of this [discussion about superintelligences] almost doesn't matter from the point of view of doing the search, if you build a good enough anomaly detector," Steve Croft, a radio astronomer who works on the Breakthrough Listen project for the Berkeley SETI Research Center at the University of California, Berkeley, said in an interview with Space.com. "We can figure out what they're up to afterwards — we may never comprehend what they're up to."

All that would matter is that we could potentially detect these intelligent life-forms' activities, even if we don't fully understand what they're doing. In some cases, though, we might understand. 

A superintelligence would need a lot of energy to facilitate the computations of its CPU. In 1964, Soviet astrophysicist Nikolai Kardashev proposed what would become known as the Kardashev scale, in which increasingly technologically developed civilizations harness the total energy of first a planet (Level I), then a star (Level II) and then an entire galaxy (Level III). 

In principle, the latter two levels would be achievable via Dyson swarms of solar-energy collectors around a civilization's home star, and then around every star and black hole in their galaxy. According to the Kardashev scale, a Type II civilization could harness 4 x 10^26 watts; a Type III civilization could reach 4 x 10^37 watts. 

A superintelligence might even opt to live inside a Dyson swarm — for example, in a "Matrioshka brain," a series of nested shells of Dyson swarms in which the innermost shell absorbs sunlight, uses the energy for processing and then emits the residual heat energy for the next shell to pick up, and so on.

What do superintelligences do in their spare time? 

What would a superintelligence do with all that energy? "Maybe they smash neutron stars together for fun and those are the fast radio bursts!" Croft said, only half-jokingly. "If you do have command of ridiculous amounts of energy, if you've achieved a Kardashev Type II or III level, then what might you do with your spare time? One thing we've seen through human societies over millennia is art, and it drives a lot of our endeavors, creating beautiful things, and I wonder whether a superintelligence might make art and whether that's something we could spot."

Spotting alien art might not be so easy; art is cultural, so we would not know what is beautiful to them. However, the scale of the potential art projects we could detect might make life easier. A superintelligence might push stars around, for example. One theoretical way of doing this is via a Shkadov thruster, which is essentially a giant concave mirror facing a star at a distance where the gravitational attraction that the mirror feels from the star is balanced by the stellar wind trying to push the mirror outward. The mirror would reflect the stellar wind and the star's own light back toward the star. And because photons and particles can carry momentum, the reflected radiation would push the star in the opposite direction. Over millions of years, it could, in theory, move the star many light-years. 

If an alien superintelligence has an artistic leaning, it may wish to assemble geometric shapes out of stars, such as a Klemperer rosette. This is a gravitationally stable system of six objects — in this case, stars — perhaps alternating in mass between large and small, all moving around a common point on the same orbit. Such a star system could not form naturally, and if we found one, it would be evidence for a powerful extraterrestrial intelligence. An alternative concept would be to place all of the planets in a system on the same orbit around their star; a recent study showed how it might be possible to fit 24 planets on the same orbit without them colliding.

However, all of these are brute-force projects. Superintelligence may be more focused on the loftier goal of just thinking, or running virtual reality programs. Processing information requires a lot of energy, and the more a superintelligence thinks, the more energy it will require. And the less ambient heat there is, the more efficiently the computations run. 

The interior of the Milky Way galaxy is a warm place, so superintelligences might relocate to the outskirts of the galaxy, where the ambient temperature drops, thus allowing more efficient information processing. Some researchers have even proposed that superintelligences might go into hibernation for tens of billions of years while the universe around them cools to just a fraction of a degree above absolute zero, which would permit more efficient computations. (Currently, the universe — or, more specifically, the cosmic microwave background, the leftover radiation from the Big Bang — is 2.73 kelvins above absolute zero.).

What would they be thinking and calculating? That's not a question we can answer, but we don't need to. All we have to do is find evidence for their presence — whether in a Dyson swarm, a Shkadov thruster, a Klemperer rosette or activity on the edge of the galaxy. And perhaps, if our own AIs arrive at the singularity too, that could give us some insight into what the great intelligences of the universe spend their time doing.

Follow Keith Cooper on Twitter @21stCenturySETI. Follow us on Twitter @Spacedotcom and on Facebook.

In popular culture, we've gotten used to aliens speaking English, or being instantly understandable with the help of a seemingly magical universal translator. In real life, it might not be so easy.

Consider the potential problems. Number one would be that any potential aliens we encounter won't be speaking a human language. Number two would be the lack of knowledge about the aliens' culture or sociology — even if we could translate, we might not understand what relevance it has to their cultural touchstones. 

Eamonn Kerins, an astrophysicist from the Jodrell Bank Centre for Astrophysics at the University of Manchester in the U.K., thinks that the aliens themselves might recognize these limitations and opt to do some of the heavy lifting for us by making their message as simple as possible.

"One might hope that aliens who want to establish contact might be attempting to make their signal as universally understandable as possible," said Kerins in a Zoom interview. "Maybe it's something as basic as a mathematical sequence, and already that conveys the one message that perhaps they hoped to send in the first place, which is that we're here, you're not alone."

Related: Could AI find alien life faster than humans, and would it tell us?

Indeed, the possibility of receiving recognizable mathematical information — pi, a burst of prime numbers in sequence (as was the case in the novel "Contact" by Carl Sagan) — has been considered in SETI for decades, but it's not the only possible message that we might receive. Other signals might be more sophisticated in their design, trying to convey more complicated concepts, and this is where we hit problem number three: That alien language could be orders of magnitude more complex than human communication. 

This is where we will need AI's help, but to understand how, first we must delve into the details behind the structure of language.

Information theory

When we talk about a signal or a message being complex, we don't mean that the aliens will necessarily be talking about complex matters. Rather, it refers to the complexity underlying the structure of their message, their language. Linguists call this "information theory," which was developed by the cryptographer and mathematician Claude Shannon who worked at Bell Labs in New Jersey in the late 1940s, and was expanded on by linguist George Zipf of Harvard University.

Information theory is a way of distilling the information content of any given communication. Shannon realized that any kind of conveyance of information  —  be it human language, the chemical exhalations of plants to attract predators to eat caterpillars on their leaves or the transmission of data down a fiber optic cable  —  can be broken down into discrete units, or bits. These are like the 'quanta' of communication, such as the letters of the alphabet or a dolphin's repertoire of whistles.

In language, these bits cannot just go in any order. There is syntax, which describes the grammatical rules that dictate how the bits can be ordered. For example: In English, a 'q' at the beginning of a word is always followed by a 'u', and then the 'u' can be followed by a limited number of letters, and so on. Now suppose there is a gap — 'qu—–k'. We know from the syntax that there are only a few combinations of letters that can fill the gap — 'ac' (quack), 'ar' (quark), 'ic' (quick) and ir (quirk). But, if the word is part of a sentence — 'The duck went qu––k' then through context we know the missing letters are 'ac'.

By knowing the rules, or syntax, we can fill in the blanks. The amount missing that still allows us to complete the word of sentence is called "Shannon entropy," and thanks to its complexity, human languages have the highest Shannon entropy of any known form natural communication on the planet.

Meanwhile, Zipf was able to quantify these basic principles of Shannon's information theory. In any communication some of the little units, these fundamental bits, will appear more often than others. For example, in human language, letters such as a e, o, t and r appear far more often than q or z. When plotted on a graph with the most common units first (on the x-axis, their rate of occurrence on the y-axis), all human languages produce a slope with a gradient of –1. At the other extreme, a baby's random babbling results in a horizontal line on the graph, with all sounds being equally likely. The more complex the communication — as the baby grows into a toddler and starts to talk, for example — the more the slope converges on a –1 gradient.

A transmission of the digits of pi, for instance, would now carry a –1 slope. So instead of searching for technosignatures, the technologically-generated signals that could mark other advanced extraterrestrial civilizations, some researchers think that SETI should be specifically looking for signals with a –1 slope, regardless of whether they appear artificial or not, and the machine-learning algorithms that carefully sift through every scrap of data collected by radio telescopes could be configured to analyze each potential signal to determine whether a signal adheres to Zipf's Law. 

Beyond that, alien communication could have a higher Shannon entropy than human language, and if it is much higher, it might make their language too difficult for humans to grasp.

But perhaps not for AI. Already, AI is being put to the test trying to understand communication from a non-human species. If it can pass that test, perhaps AI will be ready to tackle any alien messages in the future.

Interpreting dolphin communication

Denise Herzing, who is the Research Director at the Wild Dolphin Project in Jupiter, Florida, is one of the world's foremost experts in trying to understand what dolphins are saying to each other. Herzing has been swimming with dolphins and studying their communication for four decades, and has now introduced AI into the mix.

"We have two ways in which we're looking at dolphin communication, and they both use AI," Herzing told Space.com.

One way is listening to recordings of the various whistles and barks that make up the dolphins' own communication. In particular, a machine-learning algorithm is able to take a snippet of dolphin chat and break that communication down into discrete units on a spectrogram (a graph of sounds organized by frequency), just as Shannon and Zipf described, and then it labels each unique unit with a letter. These become analogous to words or letters, and Herzing is looking at the different ways they combine, or in other words their degree of order and structure.

"Right now we've identified 24 small units of sound that recombine within a spectrogram," said Herzing. "So you might have up-whistle 'A' followed by down-whistle 'B,' and so on, and this creates a symbolic code for a sequence of sound."

The machine-learning algorithm is then able to deeply analyze the sound recordings, searching for instances where that symbolic code is repeated. 

"We're looking for interesting sequences that are somehow repetitive," said Herzing. "The algorithms then look for substitutions and deletions in the sequences, so you might have the same symbolic code but one little whistle is different. That's a learning algorithm that is pretty important."

That little difference could be because it incorporates a dolphin's signature whistle (every dolphin has its own unique signature whistle, a kind of identifier like human names) or because the context is different.

This is all solidly in line with Shannon's information theory, and Herzing is also interested in Zipf's law and how closely dolphin communication replicates that –1 slope. 

"We're looking for language-like structures, because every language has a structure and a grammar that follows rules," said Herzing. "We're looking specifically for what the possibilities are for recombinational data — are our little units of sound only found alone, or do some recombine with another sound?"

Herzing's team have been searching for bigrams — occasions when two units frequently occur together, which might signify a specific phrase. More recently, they have also been searching for trigrams — where three units occur in order regularly — implying greater complexity.

Searching for meaning

This is exactly the way that AI would begin analyzing a real message embedded within a SETI signal. If the alien communication is more complex in structure and syntax than human languages then that tells us something about them; perhaps that their species is older than our own, which has given them enough time for their communication to evolve. 

However, we still wouldn't know the context of what they are saying to us in the message. This is currently one of the challenges in understanding dolphin communication. Herzing has video footage of dolphin pods to see what they were doing whenever the AI detects a repeated vocalization of symbolic code, which allows Herzing to try and infer context to the sounds.

"But if you're dealing with radio signals, how are you ever going to figure out what the context of the message is?" asks Herzing, who also takes an interest in SETI. "Looking at animal sounds is an analog for looking at alien signals, potentially to build up the tools to categorize and analyze [the signals]. But for the interpretation part? Oh boy, I don't know."

Once we have received a signal from aliens, we may want to say something back to them. The difficulty in understanding context rears its head again here, too. As Spock says in the film "Star Trek IV: The Voyage Home," when discussing responding to an alien probe, "we could replicate the sounds but not the meaning. We'd be responding in gibberish."

Herzing is trying to circumvent this context problem by mutually agreeing with the dolphins what to call things. This is the essence of CHAT (Cetacean Hearing and Telemetry), which is the second way in which researchers are using AI to try and communicate with dolphins.

In its first incarnation, CHAT was a large device strapped around the chest of the user, receiving sounds via hydrophone (underwater microphone) and then producing sound through a speaker. The modern version is smartphone-sized and worn around the wrist. The idea is not to converse in 'dolphinese,' but to agree with the dolphins upon pre-programmed sounds for certain toys that the dolphins want to play with. For example, if they want to play with a hoop, they make the agreed-upon whistle for 'hoop'. If a diver wearing the CHAT device wants a dolphin to bring them a hoop, the underwater speaker can play the whistle for "hoop." The AI's job is to recognize the agreed-upon whistle amongst all the other sounds a dolphin makes amidst all the various sources of audio interference underwater, such as bubbles and boat propellers. 

Herzing has observed that the dolphins have used the agreed-upon whistles, but in mostly different contexts. The problem, says Herzing, is spending enough time with any one particular dolphin to allow them to fully learn the agreed-upon sounds. 

With aliens, their message will have traveled many light years; any two-way communication could take decades, centuries, millennia, if it is even possible at all. So whatever information we have about the aliens will be condensed into their original transmission. If, as Kerins suspects, they send something mathematical just as a signal to us that they are there and we are not alone, then we won't have to worry about deciphering it. 

However if they do send a message that is more involved, then as Herzing is discovering with dolphins, the size of the dataset is crucial, so let's hope the aliens pack their message with information to give us and AI the best chance of at least assessing some of it.

Turn a radio telescope to the stars in the sky, and it's instantly deafened. From pulsars to radio galaxies, and ionospheric disturbances in the atmosphere to radio-frequency interference (RFI) from our own technology, the sky is a cacophony of radio noise. And somewhere, among all that, may lie a needle in a haystack: a signal from another world.

For over 60 years scientists have been scanning the skies in the search for extraterrestrial life but have yet to find any aliens. When you consider the sheer volume of search space — all those stars, all those radio frequencies — versus our limited searches so far, then it's little wonder we've not found ET yet. It's a daunting task, especially for a human.

Thankfully, we've got some non-human intelligence to join the search.

Related: AI is already helping astronomers make incredible discoveries. Here's how

The use of artificial intelligence (AI) is reaching critical mass, in our everyday lives and in science, so it is no surprise that it's now being employed in Search for Extraterrestrial Intelligence (SETI). We're not talking about Skynet, or the machines from The Matrix movies, or even Star Trek: The Next Generation's Data. The AI that is so in vogue at present is based on machine-learning algorithms designed to do very specific jobs, even if it's just to talk to you on ChatGPT.

To explain how AI is assisting in SETI, astronomer and SETI researcher Eamonn Kerins of the University of Manchester compares it to the needle in a haystack problem.

"You basically treat the data as though it's the hay," Kerins told Space.com Space.com. "Then you're asking the machine-learning algorithm to tell you if there is anything in the data that isn't hay, and that hopefully is the needle in the haystack — unless there's other stuff in the haystack too."

That other stuff is usually RFI, but the machine-learning algorithm is trained to recognize all the types of RFI we already know about. Those signals — the familiar patterns of mobile phones, local radio transmitters, electronics and so on — are the hay.

The training involves "injecting signals into the data and then the algorithm learns to look for signals that are like that," Steve Croft, an astronomer with the Breakthrough Listen SETI project at the University of California, Berkeley, told Space.com The algorithm learns to spot the patterns of these familiar signals and disregard them. Should it spot something in the data that it hasn't been trained on, then it flags this up as something interesting that requires a human to follow up on.

"There have been attempts recently at sifting through some of the Breakthrough Listen data with a machine-learning algorithm," said Kerins. "The data had already been combed through quite carefully previously by more conventional means, but yet the algorithm was still able to pick out new signals after being trained on the stuff that we know about."

This project was led by Croft and an undergraduate student, Peter Ma of the University of Toronto, who wrote the algorithm and put it to work analyzing data from 820 stars observed by the 100-meter radio telescope at Green Bank Observatory in West Virginia. The data, totaling 489 hours' worth of observations, contained millions of radio signals, almost all of which were human-made interference. The algorithm checked every single one of them and found eight signals that did not match anything it had been trained on and which had been missed by earlier analyses of the data.

These eight signals seem to come from five different star systems, although they might be misleading. They haven't been detected since — to see a signal repeat is the most basic requirement for a signal to be considered interesting in SETI — and they will probably turn out to be more RFI. However, even that's useful, because they can be used to train the next generation of machine-learning AI so similar RFI can be avoided in the future.

Machine learning algorithms can be divided into two camps. One is known as supervised learning, which is the teach-it-everything-you-know approach. Unsupervised learning is a little different, in that you just feed the algorithm the data and let it figure out what is significant, without any human biases.

"With a fully unsupervised approach you just throw all the data in, stir the pot and let the algorithm figure it out by itself," said Croft. 

As a mundane example, suppose you have a dataset of images of tables and chairs, and you want the algorithm to distinguish between them. In supervised learning, you train the algorithm on lots of images that are marked 'table' or 'chair'. With unsupervised learning, the algorithm has to distinguish between the two by grouping things that look similar without any prior training — for example, it might select anything with a back to be a chair, and anything with a long top to be a table.

Kerins highlights the example of a project led by Adam Lesnikowski of NVIDIA, who are famous for their graphics cards but which are now leaders in artificial intelligence. Lesnikowski, joined by Valentin Bickel of ETH Zurich and Daniel Angerhausen of the University of Bern, used unsupervised machine learning in a test to see whether it could spot artificial objects on the moon. The algorithm was fed images from NASA's Lunar Reconnaissance Orbiter, and it had to figure out what was a typical lunar feature, such as a crater or a rille, and what wasn't. The test was a success — the algorithm picked out the Apollo 15 lunar lander on the surface of the moon. 

The idea is that technological aliens may have already visited our solar system, and left probes or artifacts on the planets, moons or asteroids. It's possible there may even be an active probe watching us right now. 

"Some of my colleagues are very interested in the idea of having orbiters with a machine-learning algorithm on board," said Kerins. A spacecraft could survey planetary surfaces in our solar system to search for anomalies that could be alien probes, possibly millions or billions of years old now. Because unsupervised learning has the advantage of being able to function in real-time, it would be able to assess each image before moving on without having to wait to send all the data back to Earth for humans to look at.

Certainly, in the age of 'Big Data', machine-learning AI is the way forward and is now being used extensively in astronomy and in SETI, with the capability to do things faster and better than humans can.

"It's certainly fast," said Kerins. "The nearest we can get with humans is through citizen science projects."

With machine learning algorithms, humans are still intimately involved. A signal might get flagged up by the AI as being intriguing, but it is still humans who have to follow up and investigate. The algorithms aren't that smart.

A time may come soon, however, when they are that smart. Researchers at places such as Google DeepMind have been pursuing artificial general intelligence, or AGI. Whereas the algorithms we have today are very specific, AGI would be able to cast its hand to anything and learn and grow while it does. An AGI could rapidly accelerate beyond the capacity of human intelligence.

The possibilities for AGI transforming SETI are tantalizing. We've already seen how machine-learning algorithms designed to play games such as chess or Go! are developing strategies that befuddle the human experts whom the AI is beating in these games. An AGI could surely think of new ways in which to search for alien life beyond the confines of human biases and experience.

"It would be able to map out all sorts of possibilities for how language and communication can be conveyed through signals," said Kerins. "It might be able to consume vast astronomical catalogs and decide on optical strategies on how and where to look."

Steve Croft echoes Kerins' optimism. "I hope AI evolves to the stage where we can ask it to take the blinders off and imagine, from everything it knows about physics, biology, chemistry, exoplanets and technology, what it thinks ET might be doing. It will probably come up with some good ideas!"

That's if it can, or even will, tell us anything. The creation of an AGI will, in a way, by like creating an alien, one that is very much unlike us and which we might struggle to understand. 

"We might find it very hard to directly communicate with it," said Kerins. "We might have some hierarchy of translators, and at the top of that hierarchy is an intelligence that would decide on much smarter ways to look in SETI. If it makes contact, then how does that filter down to the biological intelligences, the stupid guys, us?"

We might get a version of Chinese whispers, where the relevant information is passed down through the hierarchy, getting simpler and simpler until we receive the dumbed-down version. The AGI may even withhold information that it deems would be too complicated for us to understand. If AGI managed to make a SETI detection, we may not get the full picture.

That's speculation, though. In the here and now, AI is a powerful tool that is accelerating our searches for ET. It's a sure thing that if we do discover a signal from another world in the future, we'll have AI to thank for it.

Follow Keith Cooper on Twitter @21stCenturySETI.

"Pseudoscience" has many possible definitions, and some people argue that the term shouldn't be applied at all. Perhaps the most useful definition of pseudoscience comes directly from the root words: The prefix "pseudo" is taken from the Greek word for "false," so pseudoscience is quite literally "false science."

But there is something about certain practices, like ghost hunting and astrology, that make them look like science even though they lack the underlying structures. Pseudoscience is a practice that, from the outside, looks like science, but upon closer inspection, is revealed to be nothing but. And what makes a practice look like science? To the outside world, science seems to be defined by its complex mathematics, incomprehensible jargon and dizzying array of gizmos and measurement devices.

Related: 25 space conspiracies debunked

Pseudoscience uses that same set of surface-like features; pseudoscientific practices employ their own kind of dense jargon, often feature an incredible amount of math, and even use strange and arcane measurement devices.

The soul of science

But the math, jargon and gizmos are only the "skin" of science — the surface features that are most apparent to the outside world. In other words, those are the tools that scientists use to do their jobs, the same way construction workers use hammers and saws, or lawyers use legal briefs and court motions.

Those tools don't define the job, however. Instead, underneath the surface, science has a much deeper set of practices and traditions that separate science from pseudoscience. 

While a dissection of what makes science special could encompass an entire book, a few key features of the scientific mindset make it stand out. For one, science is rigorous, which means scientists take their ideas seriously and seek to explore the full logical consequences of any hypothesis. Science is also humble, because any theory, even one that has stood for centuries, can be proved wrong at any moment. 

Next, science is skeptical, allowing for the evidence to dictate beliefs — not the other way around. Science is also open, where methods and techniques must be shared and publicized to the wider community. Science is connected, meaning that every statement a scientist makes must be linked to the broader knowledge of the entire community. Lastly, science allows itself to evolve, with new evidence and ideas supplanting earlier beliefs.

Pseudoscience in the world

This distinction between the surface features of science and the deeper core of science allows us to draw a line between pseudoscience and proper science. Pseudoscientific practices keep the surface features (the jargon, math or gizmos) while rejecting the rigor, openness, skepticism and connectedness.

For example, proponents of ancient aliens aren't skeptical and disregard any evidence that runs contrary to their existing beliefs. By contrast, SETI researchers often encourage skepticism, caution and careful analysis of data before reaching any conclusions. Astrologers keep their methods secret. Flat-Earthers don't connect their ideas to the broader understanding of how things work. 

If you encounter a belief system that seems like science at first glance but runs contrary to the underlying spirit of science, then it's probably pseudoscience. For example, if the statements of the belief system claim access to secret, inaccessible knowledge, then it's not open.

If it's static and unchanging, with evidence used to bolster the original belief and nothing else, then it's not evolving. If it's conspiratorial, claiming that the "establishment" is trying to suppress it, then it's not connected to the broader community of knowledge.

Once you gain enough practice, spotting pseudoscience is a snap. It looks like science on the outside but doesn't have the features that distinguish science as a powerful, vital way to examine the inner workings of the universe.

UFOs came to Washington today.

UFOs — or unidentified anomalous phenomena (UAP), as they're now called — have been receiving increased scrutiny from the U.S. government in recent years due to high-profile testimony from credible witnesses. In order to shine light on what some deem to be the pressing national security threat posed by UAP, the House of Representatives' Subcommittee on National Security at the Border and Foreign Affairs held a hearing Wednesday (July 26) in Washington titled "Unidentified Anomalous Phenomena: Implications on National Security, Public Safety, and Government Transparency." 

Three key witnesses testified at the hearing: Ryan Graves and David Fravor, two former U.S. Navy aviators who reported highly publicized encounters with unknown objects in military training airspace; and David Grusch, a decorated U.S. military combat veteran and Pentagon intelligence officer.

In his opening remarks, Representative Glenn Grothman (R-WI) stated that "we must demand transparency from the Department of Defense," adding that "Congress recognizes the subject of UAPs is multifaceted and requires a careful, data-driven approach." Rep. Tim Burchett (R-TN) went even further: "We need to tell the folks at the Pentagon, they work for us, that government, we don't work for them. And that's exactly the point. This is an issue of government transparency. We can't trust a government that does not trust its people."

Related: Pentagon has 'no credible evidence' of aliens or UFOs that defy physics

Echoing this further in the opening remarks, Rep. Jared Moskowitz (D-FL) stated that "the American public has a right to learn about technologies of unknown origins, non-human intelligence and unexplainable phenomena." Moskowitz added that any disclosure of classified information must be done carefully, pointing out how the existence of stealth helicopter technology wasn't publicly known before one was used in the 2011 raid on a compound housing Osama bin Laden. "But we can't allow that to be used as a shield to keep the American people completely in the dark from basic truths," Moskowitz added.

In the witness testimony that followed the opening statements, Grusch claimed he was told of the existence of a "multi-decade UAP crash retrieval and reverse-engineering program" and was denied access to it, prompting him to file the whistleblower complaint. Grusch, who served as a member of the Pentagon's short-lived UAP Task Force from 2019 to 2021, told the committee that his whistleblower complaint is based on "information I've been given by individuals with a longstanding track record of legitimacy and service to this country, many of whom also have shared compelling evidence in the form of photography, official documentation and classified oral testimony to myself and many of my various colleagues." 

Moskowitz asked Grusch if the former intelligence community official has any knowledge of "programs in the advanced tech space that are unsanctioned," to which Grusch replied that these programs do exist and are outside of congressional oversight. When asked if he was aware of imagery of crash sites of craft of unknown origin, Grusch said he cannot discuss the answer in an open, unclassified setting.

Rep. Virginia Foxx (R-NC) pushed Grusch on his claims that the U.S. government is in possession of "non-human spacecraft," asking if previous statements made by Sean Kirkpatrick, head of the Pentagon's All-Domain Anomaly Resolution Office, or AARO, were correct in stating the U.S. government had no evidence of non-human intelligence. "It's not accurate," Grusch replied.

Burchett asked Grusch if there has "ever been an active U.S. government disinformation campaign to deny the existence of unidentified aerial phenomena." Grusch affirmed there has indeed been such a campaign, yet said he can't add anything beyond what he has already stated publicly.

Rep. Eric Burlison (R-MO) also pushed Grusch on some of these statements. "You've said the U.S. has intact spacecraft. You said that the government has alien bodies or alien species. Have you seen the spacecraft? [...] Have you seen any of the bodies?" Burlison asked.  

"That's not something I have witnessed myself," Grusch replied. But he answered a subsequent question by stating definitively that, when it comes to UAP crash retrievals, "biologics came with some of these recoveries." Rep. Nancy Mace (R-SC) pushed Grusch if he meant human or non-human. "Non-human, and that was the assessment of people with direct knowledge on the program I talked to," Grusch replied.

Grusch added in response to a later question from Burchett that he is aware of "reverse-engineering programs for non-terrestrial craft."

Related: UFOs and UAP: History, sightings and mysteries

In his testimony, Graves told the committee that UAP are severely under-reported in American airspace. "These sightings are not rare or isolated. They are routine," Graves said. "Military aircrew and commercial pilots — trained observers whose lives depend on accurate identification — are frequently witnessing these phenomena." Graves described how Naval aviators operating on the U.S. East Coast witnessed objects that appeared to stay stationary in the face of hurricane-force winds before suddenly accelerating to supersonic speeds.

Despite the extraordinary nature of these sightings and their proximity to U.S. military airspace, Graves said that he and his colleagues, not to mention other pilots who have had similar encounters, have historically been hesitant to report them. "The stigma attached to UAP is real and powerful and challenges national security," Graves told the committee. "It silences commercial pilots who fear professional repercussions and discourages witnesses. It is only compounded by recent government claims questioning the credibility of eyewitness testimony. "

Graves made reference to NASA's recent UAP study group, stating the agency "has a big role to play as far as commercial aviation safety and it's one of their original charges as an organization," given that NASA already operates an Aviation Safety Reporting System.

During Fravor's testimony, the former F/A-18 pilot told the committee that he is concerned by the lack of government oversight when it comes to "processing or working on craft believed not from this world." 

"I'd like to say that the Tic Tac object we engaged in 2004 was far superior to anything that we had at the time time, have today or [are] looking to develop in the next 10 years," Fravor said. "If we in fact have programs that possess this technology, it'd be nice to have oversight from those people that the citizens of this great country elected in office to represent what is best for the United States, and best for the citizens."

In response to a question on whether or not UAP pose a potential threat to U.S. national security, Fravor stated a definitive "yes," adding that "the technology that we faced was far superior than anything that we had." Fravor called it a "travesty" that the U.S. military and/or government doesn't have a centralized repository for reports of UAP.

Grusch was also asked about a possible "interdimensional potential" to the UFO phenomenon. Grusch stated that he's familiar with concepts of "multidimensionality" and the "holographic principle," ideas about how beings might be "projected from higher-dimensional space to lower dimensional," but added that these are only theoretical.

During questioning, all three witnesses stated that it's possible UAP are interested in America's nuclear capabilities, testing for vulnerabilities in U.S. air defense systems or conducting reconnaissance in American airspace.

In closing remarks, representatives underscored how this issue, at its core, is less about hunting down evidence of alleged alien craft, and more about demanding accountability and transparency from the U.S. government. 

Rep. Robert Garcia (D-CA) reiterated the need for using science to try and find answers on the UAP enigma. "I also really believe in following facts and doing your homework and making sure that we follow science as we try to get as much information as possible," Garcia added. "Transparency is a cornerstone of government. We live in a vast galaxy. A lot of unanswered questions."

A new search for extraterrestrial life aims to find out by listening for radio pulses from the center of our galaxy. Narrow-frequency pulses are naturally emitted by stars called pulsars, but they're also used deliberately by humans in technology such as radar. Because these pulses stand out against the background radio noise of space, they're an effective way of communicating across long distances — and an appealing target to listen for when searching for alien civilizations. 

Scientists described the alien-hunting strategy in a new study, published May 30 in The Astronomical Journal. Researchers led by Cornell University graduate student Akshay Suresh developed software to detect these repetitive frequency patterns and tested it on known pulsars to be sure it could pick up the narrow frequencies. These frequency ranges are very small, at about a tenth of the width of frequencies used by a typical FM radio station. The researchers then searched data from the Green Bank Telescope in West Virginia using the method. 

Related: Are aliens real?

"Until now, radio SETI has primarily dedicated its efforts to the search for continuous signals," study coauthor Vishal Gajjar of the SETI Institute, a nonprofit organization dedicated to the search for intelligent life in the universe, said in a statement. "Our study sheds light on the remarkable energy efficiency of a train of pulses as a means of interstellar communication across vast distances. Notably, this study marks the first-ever comprehensive endeavor to conduct in-depth searches for these signals."

The researchers are listening in to the middle of the Milky Way because it is dense with stars and potentially habitable exoplanets. What's more, if intelligent aliens at the core of the Milky Way wanted to reach out to the rest of the galaxy, they could send signals sweeping across a wide array of planets, given their privileged position at the center of the galaxy. Using narrow bandwidths and repeated patterns would be a prime way for aliens to reveal themselves, as such a combination is extremely unlikely to occur naturally, study co-author Steve Croft, a project scientist with the Breakthrough Listen program, said in a separate statement. 

The method uses an algorithm that can search through 1.5 million telescope data samples in 30 minutes. Though researchers did not find any telltale signs in their first search, they say that the speed of the algorithm will help improve searches in the future.  

"Breakthrough Listen captures huge volumes of data, and Akshay’s technique provides a new method to help us search that haystack for needles that could provide tantalizing evidence of advanced extraterrestrial life forms," Croft said. 

At 3 p.m. EDT (1600 GMT) today (May 24), Europe's Trace Gas Orbiter Mars probe beamed a coded message toward Earth. Sixteen minutes later, it was received by three big radio telescopes on Earth, kicking off a global effort to decipher the cryptic signal.

That effort is A Sign in Space, a multiweek project led by Daniela de Paulis, the current artist in residence at the SETI Institute in Mountain View, California and the Green Bank Observatory in West Virginia.

"Throughout history, humanity has searched for meaning in powerful and transformative phenomena," de Paulis said in a statement.

"Receiving a message from an extraterrestrial civilization would be a profoundly transformational experience for all humankind," she added. "A Sign in Space offers the unprecedented opportunity to tangibly rehearse and prepare for this scenario through global collaboration, fostering an open-ended search for meaning across all cultures and disciplines."

Related: The search for alien life (reference)

The Green Bank Observatory is one of the three scopes that listened for the Trace Gas Orbiter's signal today, along with the SETI Institute's Allen Telescope Array in northern California and the Medicina Radio Astronomical Station in northern Italy, which is managed by the Italian National Institute for Astrophysics.

Researchers at each of those facilities will now process the signal and make it available to their colleagues around the world and to the public at large. The project team wants folks from a range of backgrounds to study the signal and try their hand at deciphering it. 

"This experiment is an opportunity for the world to learn how the SETI community, in all its diversity, will work together to receive, process, analyze and understand the meaning of a potential extraterrestrial signal," Wael Farah, project scientist for the ATA, said in the same statement.

"More than astronomy, communicating with E.T. will require a breadth of knowledge," Farah said. "With A Sign in Space, we hope to make the initial steps towards bringing a community together to meet this challenge."

You can learn more, and submit your own ideas about the message, via the project's website.

You can participate in A Sign in Space in other ways as well. 

For example, over the next six to eight weeks, the project team will host a series of Zoom meetings that will focus on the societal implications of detecting a "technosigature" from advanced alien life, among other topics. 

You can learn more about these workshops, and register to attend them, here.

At 3 p.m. EDT (1900 GMT) on Wednesday (May 24), Europe's Trace Gas Orbiter (TGO) Mars probe will send a coded message that will be received by three big radio telescopes here on Earth.

Scientists around the world — and interested members of the public — will then attempt to decode the missive, as part of an ambitious, multiweek project called A Sign in Space.

"This experiment is an opportunity for the world to learn how the SETI [search for extraterrestrial intelligence] community, in all its diversity, will work together to receive, process, analyze and understand the meaning of a potential extraterrestrial signal," Wael Farah, project scientist for the Allen Telescope Array (ATA), a network of dishes in Northern California run by the nonprofit SETI Institute, said in a statement. 

"More than astronomy, communicating with E.T. will require a breadth of knowledge," Farah said. "With A Sign in Space, we hope to make the initial steps towards bringing a community together to meet this challenge."

Related: The search for alien life (reference)

The ATA is one of the three facilities that will pick up the TGO message, which will take 16 minutes to reach Earth from Mars orbit. The other two are the Robert C. Byrd Green Bank Telescope at the Green Bank Observatory in West Virginia and the Medicina Radio Astronomical Station in northern Italy, which is managed by the Italian National Institute for Astrophysics.

Teams at each of the three observatories will process the coded signal and make it available to the public. So, if you're interested, you can try your hand at deciphering it — and submit your solution and other ideas via the project's website.

Indeed, public engagement is a key part of A Sign in Space, which is led by Daniela de Paulis, the current artist in residence at both the SETI Institute and the Green Bank Observatory.

For example, the project will host a webcast on Wednesday that features interviews with team members and live look-ins at the control rooms of the three radio telescope sites. The livestream will begin at 2:15 p.m. EDT (1815 GMT), 45 minutes before TGO beams out its message.

And, over the ensuing six to eight weeks, the project team will host a series of public Zoom meetings that will discuss the societal implications of spotting a signal from an alien civilization.

"Throughout history, humanity has searched for meaning in powerful and transformative phenomena," de Paulis said in the same statement.

"Receiving a message from an extraterrestrial civilization would be a profoundly transformational experience for all humankind," she added. "A Sign in Space offers the unprecedented opportunity to tangibly rehearse and prepare for this scenario through global collaboration, fostering an open-ended search for meaning across all cultures and disciplines."

The study determined that radio "leakage" from mobile towers here on Earth is likely detectable from nearby systems such as Barnard's Star (roughly six light-years away), provided extraterrestrials have the right equipment. Such signals are faint now but will likely increase as SpaceX continues to launch Starlink internet satellites into orbit.

The study used crowdsourced data of simulated radio signals seen from afar, with data analysis led by Ramiro Saide, an intern at the Search for Extraterrestrial Intelligence (SETI) Institute's Hat Creek Radio Observatory north of San Francisco.

Saide, also a master's student at the University of Mauritius (an island nation in the Indian Ocean), "generated models displaying the radio power that these civilizations would receive as the Earth rotates and towers rise and set," the SETI Institute wrote in a release on (May 2).

Related: Ready, SETI, go: Is there a race to contact ET?

The detectability of Earth's radio signals from afar may be faint, the researchers caution, unless E.T. has more sensitive receiving systems than ours. But there are subtleties to the data.

While traditional radio broadcasting traffic is down, more powerful radio beacons are coming online for another purpose: mobile communications. Also, countries in the Global South are making a larger contribution to radio traffic than previous decades, suggesting large economic gains in that area relative to the rest of the world.

"I've heard many colleagues suggest that the Earth has become increasingly radio quiet in recent years, a claim that I always contested," team leader Mike Garrett, a professor at the University of Manchester in England and director of the Jodrell Bank Centre for Astrophysics, said in the same statement.

"Although it’s true we have fewer powerful TV and radio transmitters today, the proliferation of mobile communication systems around the world is profound," he added. "While each system represents relatively low radio powers individually, the integrated spectrum of billions of these devices is substantial."

One extension to the research could be examining exoplanets already found by space telescopes, such as NASA's now-retired Kepler or the agency's still-active Transiting Exoplanet Survey Satellite (TESS), the team suggests.

Another direction could be parsing the sources of Earth's radio leakage, which will likely include Wi-Fi networks, radars for the military and civilian agencies, mobile handsets, and even satellite constellations such as SpaceX's Starlink.

SpaceX recently surpassed 4,000 individual active Starlinks in orbit and hopes to grow that number to at least 40,000. If SpaceX and other companies send up tens of thousands of satellites, Earth's artificial radio signal will be much easier to spot.

"Current estimates suggest we will have more than 100,000 satellites in low Earth orbit and beyond before the end of the decade. The Earth is already anomalously bright in the radio part of the spectrum," Garrett said. "If the trend continues, we could become readily detectable by any advanced civilization with the right technology."

A study based on the research was published in the Monthly Notices of the Royal Astronomical Society in February.

Elizabeth Howell is the co-author of "Why Am I Taller?" (ECW Press, 2022; with Canadian astronaut Dave Williams), a book about space medicine. Follow her on Twitter @howellspace. Follow us on Twitter @Spacedotcom or Facebook.

Those jets took out one object just off the coast of northern Alaska on Friday (Feb. 10), one over the Yukon in northwestern Canada on Saturday (Feb. 11) and another above Lake Huron on Sunday (Feb. 12), downing each one with a Sidewinder air-to-air missile.

Not much is known yet about those aerial intruders, but their origin story is likely to be somewhat prosaic. 

"There is no — again — no indication of aliens or other extraterrestrial activity with these recent takedowns," White House Press Secretary Karine Jean-Pierre said during a press conference on Monday (Feb. 13).

Related: Previous Chinese spy balloons over US were classified as UFOs: report

The three downed objects were apparently quite different than the huge balloon that an F-22 jet took out off the coast of South Carolina on Feb. 4. 

That uncrewed airship, whose 200-foot-tall (60 meters) envelope supported a truss about the size of three school buses, was a Chinese surveillance craft, U.S. officials have said. It was flying at around 60,000 feet (18,000 m) when the F-22 hit it with a Sidewinder.

The other three objects were much smaller and were flying considerably lower. The craft shot down on Friday, for example, was about the size of a small car and was cruising along at about 40,000 feet (12,000 m), U.S. officials have said. 

That lower altitude is part of the reason why the U.S. military shot down the mystery trio: They posed a potential threat to civilian aircraft, which fly at similar altitudes. (The Chinese balloon was considerably above the jetliner zone, but its apparent surveillance activities in U.S. airspace put it on the kill list.)

The U.S. military observed the three mystery objects for a spell before shooting them down, gathering some basic information. For example, all three were determined to be uncrewed, and none appeared to be sending any communications signals (though intelligence-gathering work could not be ruled out), said Adm. John Kirby, coordinator for strategic communications at the National Security Council.

In addition, "we looked to see whether they were maneuvering or had any propulsion capabilities," Kirby said during Monday's press conference. "We saw no signs of that."

Recovery teams are working to find debris from the three objects, which could tell us a lot more about where they came from and what they were doing. That could take a while, however; the northern Alaska and Yukon craft came down in remote and rugged terrain, and the Lake Huron debris is likely in deep water, Kirby said. 

Mike Wall is the author of "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or on Facebook.  

Scientists attempting to address the question, "Are we alone in the universe?" have used a new machine-learning technique to discover eight previously undetected "signals of interest" from around five nearby stars. The team applied an algorithm to previously studied data collected by the Green Bank Telescope in West Virginia as part of a campaign run by Breakthrough Listen, a privately funded initiative searching 1 million nearby stars, 100 nearby galaxies and the Milky Way's plane for signs of technologically advanced life.

And the project nearly didn't happen. "I only told my team after the paper's publication that this all started as a high-school project that wasn't really appreciated by my teachers," first author Peter Ma, now an undergraduate student at the University of Toronto in Canada, said in a statement.

Related: 10 things we learned about UFOs and aliens (or the lack thereof) in 2022

This isn't the first time that computer algorithms have been used to search the vastness of space for "technosignatures," technologically-generated signals that could mark other advanced extraterrestrial civilizations. 

However, because many algorithms used to sift through telescope data were developed decades ago for early digital computers, they are often outdated and inefficient when applied to the massive datasets generated by modern observatories. 

These classical algorithms had been used to examine the Green Bank Telescope data and this inefficiency could be why this data hadn't originally indicated any signals of interest in 2017, when scientists originally examined it. All told, the researchers analyzed 150 terabytes of data representing observations of 820 nearby stars, although they want to apply the algorithm to even more data.

"With our new technique, combined with the next generation of telescopes, we hope that machine learning can take us from searching hundreds of stars, to searching millions," Ma said in a statement.

The researchers found that the key strength of the new algorithm was to organize the data from telescopes into categories, allowing them to distinguish between real signals and "noise," or interference. Although telescopes involved in the search for technosignatures are placed in areas of the globe where there is minimal interference from human technology like cell phones, these signals still get picked up. (Most SETI programs focus on radio waves because they can travel at the speed of light across vast distances mostly unimpeded by obstacles like interstellar dust clouds; unfortunately, the very same characteristics have made radio waves the cornerstone of human communication on Earth.)

"In many of our observations, there is a lot of interference," Ma said. "We need to distinguish the exciting radio signals in space from the uninteresting radio signals from Earth."

To make sure the new algorithm wasn't confused by signals originating from Earth, Ma and the team trained their machine-learning tools to tell the difference between human-generated interference and potential extraterrestrial signals. They tested a range of algorithms, determining each algorithm's precision and how often it fell for false positives. 

The most successful algorithm combined two subtypes of machine learning: supervised learning, in which humans train the algorithm to help it generalize, and unsupervised learning that can hunt through large data sets for new hidden patterns. United in what Ma called "semi-unsupervised learning," these approaches discovered eight signals that originated from five different stars located between 30 and 90 light-years away from Earth.

The signals are convincing candidates for genuine technosignatures, according to Steve Croft, project scientist for Breakthrough Listen. "First, they are present when we look at the star and absent when we look away — as opposed to local interference, which is generally always present," he said. "Second, the signals change in frequency over time in a way that makes them appear far from the telescope."

Croft cautioned that in massive datasets that can contain millions of signals, a single signal could have both of these characteristics by sheer chance alone. "It's a bit like walking across a gravel path and finding a stone stuck in the tread of your shoe that seems to fit perfectly," he said.

So although the researchers believe these eight signals resemble what a technosignature is expected to look like, they can't confidently say any or all of the signals originate from extraterrestrial intelligence. The scientists would have needed to detect the same signals multiple times, and this repetition didn't appear during brief follow-up observations by the Green Bank Telescope.

"I am impressed by how well this approach has performed on the search for extraterrestrial intelligence," Cherry Ng, a co-author on the research and an astronomer also at the University of Toronto, said in the same statement. "With the help of artificial intelligence, I'm optimistic that we'll be able to better quantify the likelihood of the presence of extraterrestrial signals from other civilizations."

The team now wants to apply the same algorithm to data gathered by observatories like the MeerKAT array in South Africa.

"We're scaling this search effort to 1 million stars today with the MeerKAT telescope and beyond," Ma said in a second statement. "We believe that work like this will help accelerate the rate we're able to make discoveries in our grand effort to answer the question, 'Are we alone in the universe?'"

The team's research was published Monday (Jan. 30) in the journal Nature Astronomy.

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In a new study, researchers hunted for technological signs of E.T. during the moments when exoplanets pass directly in front of their suns, from Earth's point of view. These exact moments could be the perfect chance for an alien world to beam out a signal to Earthlings in an attempt to make contact. 

"Exoplanetary transits are special because they can be calculated by both us on Earth, as the observers, and also any potential technological species in the exoplanetary system itself, as the transmitters," said study leader Sofia Sheikh, a postdoctoral researcher in radio astronomy at the Search for Extraterrestrial Intelligence (SETI) Institute. These transits, then, are a predictable and repetitive time during which aliens might think to send messages and Earthlings might look to receive them. 

Related: 12 possible reasons we haven't found aliens 

"This strategy helps us narrow down the huge question of where and when to look for a message in the vast reaches of space," Sheikh told Live Science in an email. 

The new study, published Dec. 9 on the preprint site arXiv and scheduled for peer-reviewed publication in The Astronomical Journal, did not find any evidence of chatty aliens. But the study only searched a dozen far-off planets. In the future, they plan to look further with a variety of telescopes. 

Related: Is it time to send another message to intelligent aliens? Some scientists think so.

Since radio technology was invented in the late 19th century, Earth has been leaking transmissions into space — and occasionally, as with the famed Arecibo Message of 1974, has sent them out deliberately in hopes of contacting any intelligent extraterrestrial that might be listening. Hoping that intelligent alien civilizations might also leak out technological signals, or technosignals, researchers also scan the galaxy for radio waves that might have originated from alien tech. 

But the galaxy is a big place, so a key question is where to look. Sheikh and her team settled on eavesdropping on far-off exoplanets as they pass in front of their suns, in what is known as a "Schelling point" — a solution to a problem that two individuals tend to default to if they aren't communicating with one another. In other words, the moment of planetary transit just seems the logical moment to connect from the point of view of both the transmitter and receiver. 

Sheikh and her colleagues used West Virginia's Robert C. Byrd Green Bank Telescope to search for radio signals from 12 exoplanets whose transits were observable during a brief window in March 2018. They detected plenty of radio signals — almost 34,000, in fact — but 99.6% of those could be dismissed out of hand as interference from Earthbound communications. A group of trained citizen scientists did the work of examining the signals. 

In the end, all but two of the signals were determined to be due to interference. The remaining two, a couple of short bursts from Kepler-1332b and Kepler-842b — both potentially rocky planets larger than Earth — were deemed worthy of further follow-up. However, Sheikh said, those two are also almost certainly due to interference and are not real messages. 

Nevertheless, she said, the study was proof that the search method can work. The researchers plan to tackle more observations in the future at the SETI Institute's Allen Telescope Array in California. 

Originally published on LiveScience.com.

Gravitational waves ripple out when objects with mass move through space. Bigger objects — such as planets, neutron stars or black holes — produce more prominent gravitational waves. These space-time ripples were first directly detected in 2015, but since then, scientists have been getting better at spotting the waves as they lap at our cosmic shores. 

Now, new calculations published Dec. 5 to the preprint database arXiv suggest that the U.S.-based Laser Interferometer Gravitational-Wave Observatory (LIGO) can look beyond conventional sources for these space-time ripples. Colossal alien spacecraft traveling at high speeds, or pushed along by warp drives, would also produce the telltale vibrations, the authors said. 

Related: James Webb Space Telescope could help hunt for habitable alien worlds

The LIGO detector spots gravitational waves from the tiny distortions they make in space-time as they pass through it. Made up of two intersecting L-shaped detectors — each with two 2.48-mile-long (4 kilometers) arms and two identical laser beams inside — the experiment is designed such that if a gravitational wave passes through Earth, the laser light in one arm of the detector will get compressed while the other expands, creating a tiny change in relative path lengths of the beams arriving at the detector. The warpings of space-time that even the largest gravitational waves make, however, are minuscule — often the size of a few thousandths of a proton or neutron — meaning that LIGO is incredibly sensitive and requires strict maintenance and calibration.

To see how far this sensitivity could be stretched, scientists made calculations of the smallest object that would generate clearly detectable gravitational waves on Earth. It turns out, it would still be pretty big: To be detectable by LIGO, an alien mothership would need to weigh roughly the same as Jupiter, travel at one-tenth the speed of light, and be within 326,000 light-years of Earth.

Are spaceships of this scale and speed even possible? The researchers don't know, but they hope to squeeze down the ship size to more reasonable proportions as increasingly sensitive gravitational wave (GW) detectors, such as the European Space Agency's 2037 Laser Interferometer Space Antenna, are deployed. The physicists also noted that advanced alien warp drives would create gravitational wave patterns that would be distinguishable from natural sources and that, if detected, these alien waves could even provide humans with clues about how to reverse engineer the technology.

"This is because the shape of the GW signal is entirely dependent on the trajectory of the object," they wrote in the paper. "Thus, as a burst signal is detected, one can attempt to reason the qualities of the transportation mechanism present based on the shape of the GW signal."

Originally published on LiveScience.

A new analysis proposes an alternative solution to this conundrum, known as the Fermi paradox: Perhaps we're just being impatient. Maybe, with a multitude of worlds to potentially study, alien civilizations would likely wait for one to start broadcasting their presence before sending a probe. So, if we wait a few hundred or a few thousand years, somebody might come knocking.

As famed physicist Enrico Fermi purportedly said during a casual lunch conversation in 1950, "Where is everybody?' Intelligent life arose here, on Earth, but we are certainly not the only planet in the universe. Our galaxy, the Milky Way, likely contains up to a trillion worlds, and it is one of up to 2 trillion galaxies in the entire cosmos. Sure, most planets are completely inhospitable to life, but physical processes don't really happen just once. If nature can make life here, with the sheer number of other planets, it should happen elsewhere.

Related: Why are we still searching for intelligent alien life?

And presumably, some of those intelligent critters would start building spacecraft and exploring their neighborhood. Given enough time and effort, they could spread themselves or robotic emissaries far and wide. Even if they averaged only a tiny percentage of the speed of light, they could essentially swamp the entire galaxy in only a few million years.

Even if most intelligent civilizations fail in the attempt (or simply move on to other things), the fact that our galaxy has existed for over 10 billion years means that at least one civilization should have already visited our solar system, or at least left some sign of its existence.

And yet, nothing. We have absolutely no evidence for any extraterrestrial civilization, let alone life. This is Fermi's great paradox: If life can happen, it should be common, and if it's common, we should already know about it. But we don't.

Interstellar roadblocks

Over the decades, astronomers have proposed many solutions to this puzzle. One idea, called the rare Earth hypothesis, posits that perhaps life really is special and unique on the cosmic scale. In this scenario, life is so incredibly rare that we may be among the first creatures or any kind to arise in the Milky Way. In other words, the circumstances that led to the emergence of life on Earth are so special that even with trillions of other worlds, life happened essentially only once.  

Another proposed solution, known as the great filter hypothesis, postulates that perhaps life is common but intelligent life is difficult. After all, life appeared relatively early in the history of our planet, but it took billions of years for intelligence to arise, This means that perhaps we are incredibly lucky to have the brains we do. And even then, the introduction of nuclear weapons and climate change put the future of our species in doubt. So, while we may find bacteria or other simple organisms throughout the galaxy, we're unlikely to meet anybody capable of conversation.

Now, a new paper written by Amri Wandel at the Hebrew University of Jerusalem and published in the preprint database arXiv puts forward a new explanation: Because we have only recently arrived on the cosmic scene, in the sense of being able to broadcast our presence through radio transmissions, maybe we just need to wait a bit.

A game of patience

Wandel argues that while we can't imagine the technological capabilities of advanced alien civilizations, their powers aren't infinite. They still have to deal with mundane issues, like energy capture and storage, waste heat, information processing, and a finite amount of time. With up to 1 trillion potentially habitable planets in the galaxy (and even more if you include water-rich moons such as Europa and Enceladus), it seems reasonable to assume that these alien civilizations wouldn't be able to send active probes or messages to every single one.

However, it's much easier to build large, sophisticated listening stations than active probes, so the aliens would probably wait. Eventually, some intelligent civilization will arise in the galaxy and figure out the magic of radio. Inadvertently or otherwise, that civilization will start broadcasting their presence through unambiguous artificial signals. 

If the aliens were to receive a signal, they would spring into action, crafting a message of their own or even a probe to visit their new friends.

But all this takes time. A lot of it. We've been broadcasting for less than a century, meaning our "radio bubble" is less than 200 light-years wide, compared with the 100,000-light-year width of the entire Milky Way. So it may take hundreds or thousands of years for our signals to reach an alien civilization. If they respond with a signal of their own, we could get it in another few thousand years — that is, if we see it at all, because we would have to be looking in the right direction at the right time to capture it.

If the aliens decide to send a probe, it will have to crawl along the interstellar depths at a fraction of the speed of light, so it will take even longer to get here.

So maybe we're not alone after all and our galaxy is home to many other advanced civilizations. They just haven't answered our call — yet.

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The Arecibo telescope was both scientifically revolutionary and visually stunning, with a large platform suspended high above its massive dish, nestled in a tropical rainforest. Over its 57 years of operation, Arecibo contributed an astonishing body of research, including work that led to two Nobel Prizes.

It is perhaps most famous for transmitting the landmark 1974 SETI message aimed at globular cluster M13, in an attempt to reach extraterrestrial life.

Besides its scientific work, Arecibo also left a mark on pop culture, serving as the setting for the climactic fight in "GoldenEye," a 1995 James Bond film starring Pierce Brosnan. It also featured in "Contact," a 1997 film based on a novel by Carl Sagan.

History of challenges

In February 2018, the NSF — Arecibo's primary funding source since the 1970s — announced it would reduce its annual contribution from $8 million to $2 million over five years. In April 2018, the University of Central Florida in Orlando assumed management, but the facility faced escalating challenges, including damage from Hurricane Maria in 2017 and critical cable failures in 2020.

Ultimately, NSF deemed the structure beyond repair, leading to its decommissioning just weeks before its collapse on Dec. 1, 2020.

Read more: Possible cause of Arecibo Observatory telescope collapse

From military observatory to civilian astronomy

The first function of Arecibo was supposed to be studying the ionosphere, a region of the upper atmosphere that is important to understand to properly transmit radio signals, according to an NSF fact sheet. The Advanced Research Projects Agency (today's DARPA) was interested in this region to advance ballistic missile defense projects, which meant the observatory attracted military funding from the Office of Naval Research and the U.S. Air Force (as Space Force had not been created back then.)

The Air Force-managed telescope was dedicated in 1963 and hailed as the world's largest radio telescope, but in a few short years it was already facing funding issues as ARPA's research budget diminished. The NSF agreed to become Arecibo's caretaker in 1967 and the research transferred to the civilian sector and astronomy.

NASA came on board in 1971 through a cost-sharing agreement with NSF, allowing for the dish reflector to be resurfaced and for more radar equipment to be added. The partners brought in a new dome and a second line for ionospheric radar in 1997. In these decades, NSF wrote, "Arecibo became a powerful tool for scientific research focused on ionospheric physics, radar and radio astronomy, and aeronomy."

When the telescope concluded its work, Arecibo was part of the National Astronomy and Ionosphere Center. The National Science Foundation had a cooperative agreement with the three entities that operated Arecibo: SRI International, the Universities Space Research Association and Puerto Rico's Metropolitan University (UMET).

The reflective dish was 1,000 feet (305 meters) in diameter, 167 feet (51 m) deep, and covers an area of about 20 acres (81,000 square meters). A triangular platform was suspended 450 feet (137 m) above the dish by three concrete towers. The platform held the azimuth arm, a dome containing two subreflectors, and a set of antennae that could be tuned to a narrow band of frequencies.

Arecibo was the largest radio telescope until July 2016, when China finished the Five-hundred-meter Aperture Spherical Telescope's (FAST) giant dish. That dish — the size of 30 football fields — is 1,650 feet (503 m) wide.

Scientific contributions across decades

Arecibo’s legacy spans diverse fields: planetary science, astronomy, and atmospheric studies. Its radar system made pivotal discoveries, including:

1967: Determining Mercury's rotation period as 59 days (not 88 as previously thought).

1974: Detection of the first binary pulsar, leading to the 1993 Nobel Prize in Physics.

1992: Identification of the first known exoplanet system.

2016: Discovery of the first repeating fast radio burst.

Arecibo also supported asteroid monitoring, radar mapping of planets like Venus, and analysis of Earth’s ionosphere.

The 1974 Arecibo message

Arecibo broadcast its most famous message in 1974, a pictorial radio signal aimed at M13, approximately 21,000 light-years away.

According to SETI, the broadcast is roughly the same as a 20-trillion-watt omnidirectional broadcast. In simple terms, the broadcast would be visible by just about any receiver in the galaxy that is about the same size as the antenna at Arecibo.

"We translated the radio-frequency message into a warbling audio tone that was broadcast over speakers at the ceremony. When [the tone] started, much of the audience spontaneously got up and walked out of the tent and gazed up at the telescope," recalled past Arecibo director Harold Craft in a 1999 Cornell University press release marking the 25th anniversary.

In the decades following, SETI has trumpeted the message as a significant step to helping understand the challenges of communicating with aliens. "Although it's unlikely that this short inquiry will ever prompt a reply, the experiment was useful in getting us to think a bit about the difficulties of communicating across space, time, and a presumably wide culture gap," SETI wrote on its website.

Tracking asteroids, exoplanets

Arecibo was frequently used for finding asteroids that swung close to Earth. The observatory focused on those that could pose a danger to the planet, making an effort to accurately measure their sizes and gauge the potential impact they could have. (To be sure, there are no immediate threats, but scientists keep searching just in case.)

In 2013, for example, the observatory watched the arrival of asteroid 2012 DA14, which passed within 17,200 miles (27,000 kilometers) of Earth. It was a close flyby, but NASA emphasized the asteroid passed by at a safe distance.

Besides asteroid research, Arecibo was also the site of the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo. The group has a habitable planets catalog that tracks the number of alien worlds in other solar systems that could be in the Goldilocks zone, or area that is not too hot or cold for life, of their respective stars.

Decommission and collapse

On Aug. 10, 2020, one of the massive cables supporting the Arecibo Observatory radio telescope's science platform failed, leaving a 100-foot gash in the radio dish below. Although at the time scientists were optimistic about potential repairs, on Nov. 6, 2020, another cable snapped, leaving the towers and platform too unstable to repair.

That was when, on Nov. 19, 2020, the NSF declared the observatory a loss. Researchers mourned the end of the iconic structure, especially Puerto Rican astronomers. One Puerto Rican scientist, Emily Alicea-Muñoz, said that it was a point of pride for the island. "We may be a tiny little island in the middle of the Caribbean," she said, "but we can do big science."

Experts like Raquel Velho say the loss of the observatory was inevitable given the recent lack of funding for scientific infrastructure. A new inquiry was launched into the matter in February 2022 to determine what other factors, if any, created the sudden fall. While scientists remained hopeful that a new observatory would be constructed, the NSF announced in October 2022 that the funding was not available to make that happen, although they do plan to put an educational institution on the famed site.

"We were worried that it could be even worse than this, that they might say, 'OK, just close down everything,'" Abel Méndez, an astronomer at the University of Puerto Rico at Arecibo who used the telescope in his research and teaching, told Space.com when the news was announced. "But my particular hopes were higher."

Arecibo legacy

While Arecibo itself is no longer operational, its data always will be accessible through an archive and will allow scientists to make discoveries indefinitely. The telescope collected 57 years of data on pulsars, asteroids, galaxies, planets and many more interesting objects around the solar system and universe at large.

The impact of the Arecibo's loss was felt around the globe. And not just by researchers, since the observatory became "potently symbolic, almost sacred" to those touched by the facility, according to science writer Nadia Drake. Drake's family had been involved with Arecibo research for decades, particularly through her father Frank's work with Project Ozma.

In a 2021 presentation at the 52nd Lunar and Planetary Science Conference (LPSC), presenters wrote that Arecibo left an "indelible mark on planetary science, radio astronomy, and space and atmospheric sciences," and they expressed the sorrow surrounding its collapse in a wistful haiku: "Six decades' service / Arecibo's telescope / Lost, not forgotten."

Additional resources

Watch an in-depth engineering video explaining why the Arecibo Telescope collapsed. Witness Arecibo's decades of work with oral histories, written accounts and newspaper articles in this Cornell University guide.

References

Arecibo Observatory. (n.d.) https://www.naic.edu/ao/landing

Cornell Chronicle. (1999, Nov. 12.) "It's the 25th anniversary of Earth's first attempt to phone E.T." https://news.cornell.edu/stories/1999/11/25th-anniversary-first-attempt-phone-et-0

Drake, Nadia. (2021, Jan. 11.) "Why the loss of an iconic radio telescope is painfully personal." National Geographic. https://www.nationalgeographic.com/science/article/why-the-loss-of-an-iconic-radio-telescope-is-painfully-personal

Gonzalez Kotala, Zenaida. (2018, Aug. 14.) "Arecibo Observatory to Get $5.8 Million Upgrade to Expand View." University of Central Florida. https://www.ucf.edu/news/arecibo-observatory-get-5-8-million-upgrade-expand-view/

National Science Foundation. (n.d.) "Arecibo: Facts and Figures." https://www.nsf.gov/news/special_reports/arecibo/Arecibo_Fact_Sheet_11_20.pdf

National Science Foundation. (2022). "Arecibo Observatory: Media Resources." https://www.nsf.gov/news/special_reports/arecibo/

SETI Institute. (2022.) "Arecibo Message." https://www.seti.org/seti-institute/project/details/arecibo-message

SETI Institute. (2022.) "Project Ozma." https://www.seti.org/project-ozma

Taylor, P.A. and Rivera-Valentin, E.G. "The Legacy of Arecibo Observatory in Planetary Science and Beyond." 52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548). https://www.hou.usra.edu/meetings/lpsc2021/pdf/2179.pdf

While the investigation of the so-called Wow! signal came up empty this time, the research team said the collaboration shows promise in making other searches for intelligent alien life outside of Earth. This will even involve looking at data from the sky-mapping Gaia spacecraft to find more sun-like stars in the region of the signal, project collaborator Wael Farah told Space.com.

"This does not only include the Wow! signal uncertainty region ... but extends to areas on the sky where stellar densities are high, like the galactic center and galactic disc," Farah wrote in an email Monday (Nov. 7).

The targeted zone was around a sun-like star located 1,800 light-years away in the constellation Sagittarius, which was identified as a possible zone for the signal in research published in May. "This is the first time a targeted search for the Wow! signal has been conducted," Karen Perez, graduate student at Columbia University, said in a Sept. 29 release about the research, which Perez led. It was conducted by Breakthrough Listen, a program of the Search for Extraterrestrial Intelligence (SETI) Institute.

Related: Contact with ET: How would humanity react?

The Wow! Signal blasted from space via radio on Aug. 15, 1977, but despite its regular pattern during a brief span, no one has found any concrete evidence of a repeat signal in the 45 years since that eventful evening. (The name comes from the word "Wow!" that a researcher scrawled on a printout showing the signal.)

Perez noted the search spurred the first-ever collaboration between two telescopes funded by SETI: the Green Bank Telescope and the Allen Telescope Array. The telescopes made their observations on the same day, on May 21, with Green Bank conducting two 30-minute observations and ATA making six five-minute observations. Their observations also overlapped for almost 10 minutes, SETI said in the statement.

Farah, a postdoctoral researcher working at ATA, said the telescope's large field of view and other capabilities (like placing more search beams in the sky) will allow "many more sources [to] be identified and studied simultaneously with the instrument." In other words, more candidate stars where the signal originated might pop up in future searches of the region.

A paper based on the research was published in Research Notes of the American Astronomical Society. Open data about the search is available at this SETI site.

Elizabeth Howell is the co-author of "Why Am I Taller?" (ECW Press, 2022; with Canadian astronaut Dave Williams), a book about space medicine. Follow her on Twitter @howellspace. Follow us on Twitter @Spacedotcom or Facebook.

That's why, for the first time in 35 years, a team of policy experts and scientists have united to establish a set of alien-contact protocols for the entire world to follow in the event of a sudden encounter with E.T. 

"Science fiction is awash with explorations of the impact on human society following discovery of, and even encounters with, life or intelligence elsewhere," John Elliot, a computer scientist at the University of St. Andrews in Scotland, said in a statement. Elliot is the coordinator of the University of St. Andrews' newly established SETI Detection Hub, the cross-disciplinary organization that will establish the new alien contact protocol. 

Related: 9 Strange, Scientific Excuses for Why Humans Haven't Found Aliens Yet

According to Elliot, the new research group will "go beyond thinking about the impact on humanity" of a potential alien encounter and start focusing on how we should respond instead. 

Currently, the only alien contact protocol that humans have was established by the Search for Extraterrestrial Intelligence Institute (SETI) community in 1989. The protocol, which was last revised more than a decade ago, is vague when it comes to the international response to extraterrestrial communication; it mainly focuses on the importance of sharing discoveries with the public and broader scientific community. In the event of confirmed alien contact, the protocol's main practical tip for scientists is to seek instruction from the United Nations or another governing body. (What the United Nations should do is another open question.)

From finding traces of water on Mars to discovering potentially Earth-like exoplanets, advances in space exploration in recent decades have made the idea of life on other worlds more plausible. Yet despite more than a century of efforts to get in contact with these potential lifeforms, humans have yet to hear back.

Rather than focusing on sending messages to aliens, the new SETI Detection Hub will scan signals for potential messages sent from alien lifeforms and will develop a framework for attaching meaning to those signals. They'll also create impact assessments; deliver reports that outline the implications of specific policies; and develop protocols and treatises for responding to hypothetical alien messengers. 

"Will we ever get a message from E.T.? We don't know. We also don't know when this is going to happen,"" Elliot said. "But we do know that we cannot afford to be ill-prepared — scientifically, socially, and politically rudderless — for an event that could turn into reality as early as tomorrow."

While conspiracy theories about potential alien visitors to Earth have abounded recently, the U.S. Department of Defense filed a report this week claiming there's no evidence of extraterrestrial visitors in more than 140 cases of unidentified aerial phenomena (UAPs) reported by the U.S. military. Foreign spy drones and "airborne clutter," like weather balloons, are the far more common explanations for oddities in America's skies. At least, for now.

Originally published on Live Science.

In a new paper, scientists outline how we can look for clues any visitors may have left behind.

The search for extraterrestrial artifacts 

There are several main methods for hunting for intelligence outside Earth. The first approach is to look for signs of any kind of life at all, intelligent or otherwise. This is by far the most common method in astronomy, and is usually targeted at other star systems — for example, looking for life-generated chemicals in the atmospheres of other worlds. But the search for extraterrestrial life also considers places within the solar system, like the surface of Mars and the hydrocarbon-rich atmosphere of Saturn's moon Titan.

Another approach is to look specifically for intelligent life, because presumably, intelligent aliens are capable of making their presence known far more easily than a microbe is. For instance, we can look for communicative aliens that are broadcasting their existence in radio or optical wavelengths. Looking for artificial radio signals is the bread and butter of the search for extraterrestrial intelligence (SETI).

Related: Why are we still searching for intelligent alien life?

But intelligent aliens may also leave other clues. If they become capable of building so-called megastructures, like Dyson swarms, then we can detect those megastructures in searches of other systems. For example, enough large structures around a star would alter the light we see and could be a sign of intelligent activity.

So far, all searches for extraterrestrial life have come up empty. But there is another avenue that is relatively unexplored: the search for extraterrestrial artifacts (SETA). The idea behind this approach is that if aliens become advanced enough, they might want to explore the galaxy, either by themselves or through robotic spacecraft. In the roughly 4.5 billion-year history of the solar system, these aliens would have had plenty of time to swing by our neighborhood and maybe leave a mark.

The leftovers 

In contrast to SETI, SETA allows astronomers to dig deep into the past. They don't have to hope to catch a radio signal from a civilization that is active at the same time we're listening. In fact, multiple civilizations could have come and gone throughout the galaxy, each one leaving something behind in our solar system before fading from existence (or moving on to something more interesting).

In a new paper posted to the preprint database arXiv, astronomers proposed a strategy for using existing telescopes, surveys and planetary probes to hunt for signs of past alien visits. They discuss three categories of remnants we might detect.

The first category is regular surface artifacts — dead and leftover spacecraft, probes and even just trash. In humanity's comparatively short time exploring the solar system, we've littered the moon and Mars with dozens of defunct spacecraft and random pieces of junk, so it's not implausible to suspect that a visiting alien civilization would do the same. Plus, because many surfaces in the solar system do not experience weathering or volcanism, an artifact left there could be noticeable for billions of years.

Along with surface artifacts, there can be spacecraft hanging out in interplanetary space — a category commonly known as "lurkers." They might wait in a stable gravitational Lagrange point or orbit some distant moon. They might be active, monitoring and recording interesting things happening in the solar system, or they might be long dead and not look much different from an asteroid or a comet.

Lastly, we might encounter interstellar artifacts, ones that are never meant to stay put in any one star system but aimlessly wander the galaxy, traipsing from one system to another. We already have several means of detecting these kinds of artifacts, like broad astronomical survey telescopes and planetary missions.

Signs of damage done 

Speaking of travel, we might have the capability with existing surveys to find evidence of interstellar and interplanetary adventures. For example, any interstellar spacecraft worth its salt will need some method of propulsion. And because even aliens have to obey Newton's laws, there will have to be some kind of exhaust to propel the spacecraft. The faster we want the craft to go, the more powerful its exhaust will have to be, potentially making it visible to the James Webb Space Telescope or the Chandra X-ray Observatory.

Interstellar travel could also involve laser propulsion via lightsail, which could be detectable. Or we might find evidence from more subtle clues, like gravitational anomalies — orbits of small objects that don't quite make sense because they might have been perturbed by a passing craft.

Lastly, we can search for signs of past interference, rather than just passive observation, in the solar system. If aliens opened up a strip mine on Mercury, for example, we would still be able to see it today. Or if heavy equipment is still active, it would have a bit of waste heat associated with it, which would stand out against the radiation emitted by the surface of a planet or moon. Lastly, we may be able to find geochemical anomalies — the result of tinkering with chemical processes on a world (or just outright pollution).

The authors highlighted how we could use current and planned observatories and solar system probes to hunt for these artifacts without having to change their mission parameters. If we're already scanning the surfaces of planets and imaging large swaths of the solar system, we can piggyback on these campaigns to search for evidence of extraterrestrial life.

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