alien research paper

Watch CBS News

Aliens could be "walking among us" on Earth, Harvard researchers suggest

By Neal Riley

Updated on: July 2, 2024 / 11:55 AM EDT / CBS Boston

CAMBRIDGE - Are we alone in the universe? A recent paper from researchers at Harvard University puts an interesting twist on one of humanity's biggest questions.

The paper , which is not affiliated with the university, addresses a resurgent interest in UFOs , known officially as Unidentified Anomalous Phenomena or UAPs by the government. The United States is tracking more than 650 potential UFOs , a Pentagon official said last year.

Harvard researchers Tim Lomas, Brendan Case and Montana Technological University professor Michael Masters put forward a "cryptoterrestrial hypothesis" for the UFOs, theorizing that there's a "concealed earthly explanation" for the sightings. They argue scientists should seriously consider this possibility, alongside explanations that pilots are actually seeing human-made technology or something from an advanced civilization in another part of space. 

"We've seen these cockpit videos so many times ... but what's inside?" Masters said in an interview with CBS News Boston.

What is the cryptoterrestrial hypothesis?

The trio explains that the cryptoterrestrial hypothesis suggests that the intelligent beings responsible for the UFOs may be "concealed in stealth" on Earth or nearby. That could mean they are underground, on the far side of the moon or "even walking among us" and passing as humans.

"We're not saying this is right, we're not saying that this is absolutely 100% the case, we're saying these are some potentialities, these are some possibilities to help explain the origin of these beings," Masters said.

Masters is a biological anthropologist who said he was asked to help research potential explanations for UFOs. He said "aliens" may actually just be humans from far in the future who have figured out how to time travel. 

Are aliens just humans from the future?

Masters said the beings in reported alien encounters are "ubiquitously described as looking just like us." He argues it's highly unlikely that aliens looking just like humans would be from another planet. It "may simply be that they're us," he said. 

"We may go on to look like them," Masters said, referring to typical depictions of "little green men." "Based on our evolutionary characteristics over the last 6 to 8 million years, we are arguably going to have bigger heads, smaller faces, more advanced technology and a lot of these traits are described in association with these beings."

He speculates that the intelligent beings may have "gone underground until we're ready for contact."

"We must seem extremely primitive to them based on what we see flying around in the skies," Masters said.

"Something that we should all be talking about"

A Pentagon report released this year says there's no evidence that any UAP sighting "represented extraterrestrial technology." And while the researchers acknowledge that their paper is "a speculative thought piece," they say it still deserves serious consideration.

"It is something that we should all be talking about," Masters said. 

He said technology from the future could help humans tackle the big problems they face today, such as climate change .

"What if we all just opened our minds to the fact that there's this thing much bigger than us right now, and what could we learn from it?" he said. 

Neal J. Riley is a digital producer for CBS Boston. He has been with WBZ-TV since 2014. His work has appeared in The Boston Globe and The San Francisco Chronicle. Neal is a graduate of Boston University.

Featured Local Savings

More from cbs news.

Mass will spray for mosquitos after first human case of EEE

"Person of interest" sought in Worcester double homicide

Why Elizabeth Warren teared up during lengthy ovation at DNC

Boston man inspired by brother who died from gun violence brings hope to youth

An official website of the United States government

The .gov means it’s official. Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

The site is secure. The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

• Publications
• Account settings

Preview improvements coming to the PMC website in October 2024. Learn More or Try it out now .

• Advanced Search
• Journal List
• Astrobiology

Alien Mindscapes—A Perspective on the Search for Extraterrestrial Intelligence

Advances in planetary and space sciences, astrobiology, and life and cognitive sciences, combined with developments in communication theory, bioneural computing, machine learning, and big data analysis, create new opportunities to explore the probabilistic nature of alien life. Brought together in a multidisciplinary approach, they have the potential to support an integrated and expanded Search for Extraterrestrial Intelligence (SETI 1 ), a search that includes looking for life as we do not know it. This approach will augment the odds of detecting a signal by broadening our understanding of the evolutionary and systemic components in the search for extraterrestrial intelligence (ETI), provide more targets for radio and optical SETI, and identify new ways of decoding and coding messages using universal markers. Key Words: SETI—Astrobiology—Coevolution of Earth and life—Planetary habitability and biosignatures. Astrobiology 16, 661–676.

1. Introduction

T he Kepler mission and ground-based observatories have revealed thousands of exoplanets in small sectors of our galaxy alone, thus providing powerful evidence that our solar system is not an exception but simply one out of countless others in the Universe ( e.g. , Borucki et al. , 2010 ; Kopparapu et al. , 2013 ; Seager, 2013 ; Batalha, 2014 ; Gaidos et al. , 2014 ; Hatzes, 2014 ; Quintana et al. , 2014 ; Macintosh et al. , 2015 ). What remains unanswered, however, is whether life—simple or complex—exists beyond Earth.

For nearly 20 years, astrobiology has brought a multidisciplinary vision to this quest through three fundamental science questions: (1) How does life begin and evolve? (2) Does life exist elsewhere in the Universe? (3) What is the future of life on Earth and beyond? In the 2008 version of its roadmap (Des Marais et al. , 2008 ), astrobiology proposed a global approach to these questions through a broad research program with the goals to understand the formation and evolution of habitable planets, to explore and characterize the evolution of planetary environments favorable to life's development in the Solar System and beyond, and to find methods to detect the signatures of life on early Earth and other worlds.

Thirty-five years before the creation of astrobiology, a very similar intellectual approach had been articulated by Frank Drake in the “Drake equation” ( Section 2 ) but with a different intent. The Drake equation provided a probabilistic model to estimate the number of actively communicating extraterrestrial civilizations in the Milky Way, and was formulated around a technological imperative (radio astronomy) and a philosophical question: Are we alone?

Decades of perspective on both astrobiology and the Search for Extraterrestrial Intelligence (SETI) show how the former has blossomed into a dynamic and self-regenerating field that continues to create new research areas with time, whereas funding struggles (Garber, 1999 ) have left the latter starved of young researchers and in search of both a long-term vision and a development program. A more foundational reason may be that, from the outset, SETI is an all-or-nothing venture where finding a signal would be a world-changing discovery, while astrobiology is associated with related fields of inquiry in which incremental progress is always being made.

Yet in the same way astrobiology approaches the understanding of life in the Universe, SETI carries in its quest fundamental and unique questions that are central to the understanding of who, what, and where intelligent life is, and how to find it. While Are we alone? is their philosophical and popular expression (Zuckerman and Tarter, 1979 ; Tarter and Chyba, 1999 ), their scientific formulation can be expressed in these questions: How abundant and diverse is intelligent life in the Universe? How does intelligent life communicate? How can we detect it? If understanding life is the thread woven through the astrobiology roadmap, understanding how intelligent life interacts with its environment and communicates information is central to SETI.

In the following sections, we examine how scientific and technological advances are now allowing us to explore these questions in ways that were not previously possible, and to build the foundation of a long-term, multidisciplinary, and integrated vision for SETI. Here, we offer a perspective on how we could scientifically augment the odds of finding extraterrestrial life (ET) and an invitation to change our mind-set in doing so.

2. Historical Pathway to ET

While the scientific foundation for a living universe was established in the 16 th century with the Copernican revolution, the nature of advanced civilizations remained the domain of philosophers and fiction writers for a few more centuries ( e.g. , Descartes, 1644 ; de Fontenelle, 1686 ; Voltaire, 1752/2002 ; Kant, 1755/2009 ; Swendenborg, 1758 ; Flammarion, 1872 —reviews by Dick, 1984 ; Crowe, 2011 ). The latter populated the Universe and our psyche with beings and worlds that were no more than idyllic or nightmarish versions of ourselves, our society, and our biosphere. By the end of the 19 th century, the advent of new technologies opened a different epistemological chapter for SETI. At that point, the quest for alien civilizations started to transition from a justifiable belief to a technology-based endeavor. Electricity and radio were first proposed as means to communicate with our close neighbor (Seifer, 1996 ) after Schiaparelli described channels— canali , in Italian—on Mars that later, Lowell ( 1906 ) erroneously claimed were artificial canals constructed by Martians. Over a half-century later, Cocconi and Morrison ( 1959 ) became the first to point out the possibility of searching for aliens in the microwave spectrum. Their expectation was that extraterrestrial signals could be pulse-modulated ( e.g., Shostak, 2011a ), and they proposed to examine solar-mass and red dwarf stars within 15–50 light-years of Earth.

The conclusion of their article in Nature contained key comments that still resonate today. These comments include the realization that technology was finally available to test scientific hypotheses consistent with observational and theoretical astronomy, an understanding of the transformative philosophical and practical implications of a potential contact with an alien civilization ( e.g., Almár and Tarter, 2011 ; Eliott, 2011a ), and a concern that their work would be consigned to science fiction by many.

Independently from Cocconi and Morrison, astronomer Frank Drake had been formulating similar plans to conduct an actual search, and within a year of the publication, Project Ozma was launched at Green Bank (Schuch, 2011 ). Modern SETI was born and set out to search for ET's presence through narrowband radio astronomy. Broadband optical astronomy became an additional search tool in 1998 with OSETI (Ansbro, 2001 ), although the idea was previously suggested by physics Nobel laureate Charles Townes, whose research led to the maser and the laser ( e.g., Schwartz and Townes, 1961 ; Wright et al. , 2014 ).

Since 1961, SETI's intellectual framework has been centered on a probabilistic argument, the now-famous Drake equation:

where N is the number of civilizations in the Milky Way whose electromagnetic emissions are detectable; R * is the average rate of star formation in our galaxy; f p is the fraction of those stars with planetary systems; n e is the number of planets, per solar system, with an environment suitable for life; f l is the fraction of these planets that actually develop life; f i is the fraction of life-bearing planets that develop intelligent life; f c is the fraction of civilizations that develop a technology that releases detectable signs of their existence into space; and L is the length of time such civilizations release detectable signals into space. For reviews and discussions about the Drake equation, see, for example, the works of Shostak ( 1998 ), Vakoch and Harrison ( 2011 ), Maccone ( 2012 ), Vakoch ( 2014 ), Vakoch and Dowd ( 2015 ), and Darling and Schulze-Makuch ( 2016 ).

Both lauded and criticized from the day it was formulated, the Drake equation clearly represented a watershed moment in science that gave humanity a glyph with which to spell alien life for the first time. Included as a forethought to the 1961 Green Bank Search for Extraterrestrial Intelligence meeting agenda (Drake, 2011 ), the so-called equation proved to be anything but. Consisting of a combination of quantitative and speculative factors that were solely meant to engage a discussion within the scientific community on the potential number of extraterrestrial civilizations willing and able to communicate in our galaxy, it quickly became SETI's signature. In hindsight, it was much more.

3. A Roadmap

The term equation is misleading in this context. Nor does the label probabilistic argument fully capture what the formulation truly represents, and the succession of some of its variables could be criticized. For instance, between f i and f c the notion of intelligence abruptly gives way to that of civilization, when they are, in fact, distinct notions. On our planet, one has not been demonstrated to necessarily lead to the other. Earth has developed a number of intelligent species, some of which use tools, while others are organized in hierarchical societies. Ultimately, the term technological civilization is what differentiates humankind, that is, an advanced stage of social development and organization, where scientific knowledge is applied for practical purposes on an industrial scale. In our case, this technology allows our species to scientifically explore and characterize our planet, the Solar System, and the Universe—and, on Earth, this is unique to the human species.

Nevertheless, the Drake equation was essentially the first roadmap and the first holistic vision of the search for life in the Universe (Tarter, 2007 )—an approach that would become the trademark of the nascent field of astrobiology 35 years later (Des Marais et al. , 2008 ). Even at this seminal time, it captured in one expression the notions of extrasolar planetary systems, habitable zones, habitable planets and environments, the transition from chemistry to biology, life on and beyond Earth, and the evolution of intelligence, civilization, and technology.

In the epistemological sense, the Drake equation provided a reductionist approach by scientifically breaking down the question of technologically advanced civilizations into simpler and smaller parts (the variables). Ultimately, it overlooked its own revolutionary vision as SETI focused on the application of one technology to search for Sun-like stars and red dwarfs ( e.g. , Tarter, 1979 , 2004 ; Billingham et al. , 1980 ; Gulkis et al. , 1981 ; Heath et al. , 1998 ; Turnbull and Tarter, 2003 ; Tarter et al. , 2007 ). This rationale remains largely unchanged today despite advances in exploration and science that are relevant to the factors of the equation. As it stands, SETI does not search for all life or for all intelligent life. It focuses exclusively on technologically advanced life.

At the time of its formulation, the Drake equation was simply meant to be a tool to gauge how many technologically advanced civilizations might be “out there.” The focus was clearly on the end-number ( N ) to evaluate whether radio astronomy and astrophysics could provide successful strategies to intercept ET's signal across interstellar distances (Tarter, 2001a ). The focus was not on trying to understand or quantify the processes taking place within each of the factors that lead to the next. Drake himself stated that his equation was not aimed at searching for primordial or primitive life-forms (Drake, 2011 ). Rather, it was aimed at the radio search. This explains SETI's path from the moment the Tatel Telescope at Green Bank was turned toward Tau Ceti and Epsilon Eridani for the first time. This might also explain why the radio receivers have remained silent since (see Sections 4 and 5 ).

Over the years, and with the exception of a clear connection to exoplanet detection (Tarter, 2001a , 2001b ; Harp et al. , 2015 ) and other astronomical fields, SETI around the world has evolved, for most, independently from core disciplines that rightly should be considered central to its understanding of what alien life could be and, therefore, to an understanding of how to optimize a detection strategy. While individual efforts exist, they have yet to be integrated into one vision and effectively support each other and existing projects ( e.g., Fig. 1 ). It could be argued, but with only partial justification, that the reasons for SETI's all-or-nothing venture are grounded in historical circumstances. Very little data were available to quantify the factors of the Drake equation at the time it was formulated, and most knowledge about the Solar System and the Universe was still primarily coming from ground-based astronomy and astrophysics. President Kennedy was a year away from declaring the race to the Moon, and orbiters were sent to Mars and Venus for the first time. It was a time of discoveries to come, in which the young science of radio astronomy was viewed as a unique tool to help humanity make what would be a world-altering discovery.

Example of an integrated path to ET detection showing basic science questions ( e.g. , who and what are we searching for, and where? ), key multidisciplinary science concepts, and relevant exploration methods ( how do we investigate? ). The combination of questions and approaches results in a directed and scientifically rich vision to ET detection, whose output is a reasoned exploration target. Since 1960, SETI's exploration strategy has prioritized the detection method (radio and optical searches) without addressing the fundamental nature of who and what ET could be, which has fundamental implications for where and how to search for it. The science concepts and methods shown here are discussed in the text.

4. The Evolution of N in the Past Decades

By contrast to this time, large databases are now available in many relevant fields—and not necessarily only in astronomy—but their integration to SETI's approach has been slow in coming. Yet the means are currently in place to substantially increase the odds of finding ET through the development of an expanded search strategy that reflects this new knowledge.

4.1. Searching for ourselves

Part of this expanded vision starts by acknowledging that so far, in our quest to find ET, we have only been searching for other versions of ourselves, making the odds of success possibly more daunting than already dictated by nature. While the first variables of the equation are astronomical, observable, measurable, and most likely universal, as we move to the right, they become local, and the transition from life to intelligence to civilization and technology does not even characterize the average life-form on Earth. It characterizes us humans, a statistical outlier on our own planet.

Searching for other versions of ourselves is not unique to SETI. This is equally true of astrobiology, and it makes perfect sense as a starting point. After all, this is the only model of life we know, and a model that has been proven on our planet. Such an exploration strategy is further vindicated by the fact that the basic elements of life as we know it (CHONPS) are common in the Universe (Bada et al. , 1994 ; Dyson, 1999 ; Seckbach et al. , 2004 ; Brack, 2005 ; Mandell, 2008 ; Gibb, 2013 ), and habitable environments for life as we know them seem plentiful. Moreover, the Kepler mission and ground-based data suggest that there could be as many as 40 billion Earth-like planets in our galaxy alone (Petigura et al. , 2013 ), 25% of them around Sun-like stars. Other models suggest that there could be up to 700 trillion planets in the Universe, but the vast majority would be far older than Earth (Zackrisson et al. , 2016 ). Using a Biological Complexity Index, Irwin et al. ( 2014 ) proposed the existence of ∼100 million planets in the Milky Way where complex life could have evolved. However, as they note, complex life does not necessarily mean technologically advanced life.

Although encouraging, large numbers do not tell the whole story. Zackrisson's study suggests that these worlds are likely to be very different from our planet, while other studies take the extreme position that Earth could be unique (Ward and Brownlee, 2003 ). In addition to the possible issues of age and composition, fundamental questions have now emerged from space, planetary, and earth sciences that directly bear on the question of planetary habitability as we know it, life beyond Earth, and its potential evolutionary tracks. These questions include the following:

Is there a generational aspect to the rise of life in the Universe depending on elements delivered by dying stars ( e.g., Cowan and Sneden, 2006 )? Did the configuration of the Solar System play a role in the successful development and survival of life on Earth ( e.g., star, planets, their composition, size, and position)? In particular, did planets the size of Jupiter and Saturn protect life on Earth by attracting most cosmic debris (Horner et al. , 2013 ) or, alternatively, foster the development of life on Earth by helping the delivery of volatile materials from the outer Solar System needed for life to form (Grazier, 2016 )? Did our moon play a critical role in the rise of biology by stabilizing Earth's climate (Laskar et al. , 1993 ; Lissauer et al. , 2011 )? How did Earth transition from prebiotic chemistry to life (Lazcano and Miller, 1996 ; Pascal et al. , 2006 ; Fitz et al. , 2007 ; McCollom, 2013 ; Ruiz-Mirazo et al. , 2013 ; Imari Walker, 2014 ; Walker, 2014 )? Does environmental stability foster or inhibit life's inception, survival, and evolution; or does it take a mix of stability and chaos to stimulate biochemistry and biodiversity (Rosenfeld, 2011 )? Do plate tectonics and oceans play a critical role in prebiotic and biotic processes (Spohn, 1991 ; Heller et al. , 2011 ; Stern, 2015 )—and are they critical individually or collectively (Kasting, 1993 ; Martin et al. , 2008 ; Golding and Glikson, 2011 ; Lyons et al. , 2014 )? The most basic of all these questions remains today without an answer: What is life?

These are just a few examples, but the answer to each question has the power to deeply shape the vision of what the potential for an “Earth-like” planet to harbor life really means, and will affect the probability for such a planet to develop advanced and technological life.

4.2. Evolutionary and systemic approach to N

Progressing to the right of the Drake equation, astronomy and biology are linked through two concepts: habitable zone and environmental habitability ( e.g. , Cockell et al. , 2016 ). Both notions are mutable in space and time, the latter even more so than the former; and on Earth, climate change, extreme terrestrial environments, and genomics demonstrate how fast environmental changes can happen and how much the evolution of life and environment are intertwined (Golding and Glikson, 2011 ). While the initial astronomical and physicochemical conditions may drive the type of prebiotic chemistry possible on a planet, life, as demonstrated on Earth, becomes a primary player in shaping its environment as soon as it takes hold ( e.g. , atmosphere, landscape, mineralogy). This is the fundamental concept of coevolution of life and environment ( e.g., Watson, 1999 ; Kooijman, 2004 ; Dietrich et al. , 2006 ; Knoll, 2009 ; Grenfell et al. , 2010 ; Kolb, 2014 ). This coevolution will dictate the uniqueness of each planetary experiment (Irwin and Schulze-Makuch, 2001 ; Schulze-Makuch et al. , 2013 ) and will do so not only when (or if) life reaches the stage of technological advancement. It will start from the very first moment, as it did on Earth.

Earth's biosphere, and all events that led to us, and the way we perceive the environment and the Universe are the result of over 4 billion years of reciprocal influences between environmental and biological processes (Fabbro et al. , 2015 ; Houri-Ze'evi et al. , 2016 ). They are the result of evolutionary bottlenecks induced by geological, climatic, and cosmic events (Lynch and Lande, 1993 ; Bürger and Lynch, 1995 ; Bijlsma et al. , 2013 ). An asteroid impacting instead of missing Earth would completely alter the course of evolution at any time.

Ultimately, biological evolution on Earth has been partially dictated by somewhat predictable cycles and events (astronomical, climate) but drastically more so by stochastic events, both geological and biological in nature ( Fig. 2 ) (Pigliucci and Müller, 2010 ), by when and where they occurred and at what stage of evolution they happened (Gould, 1998 ; Raup, 1999 ; Schulze-Makuch and Irwin, 2001 ; Schulze-Makuch et al. , 2013 ; Keller and Kerr, 2014 ; Lehman and Miikkulainen, 2015 ). It follows that, even considering panspermia and planetary exchange as primary seeding mechanisms ( e.g. , Arrhenius, 1907 ; Arrhenius and Mojzsis, 1996 ; Melosh, 1996 ; Burchell et al. , 2004 ; Napier, 2004 ; Gladman et al. , 2005 ; Owen, 2008 ; Worth et al. , 2013 ), two planets with absolutely similar environments and receiving absolutely similar seeding material may have two very distinct biological destinies depending on when extinctions and evolutionary bottlenecks take place, and whether these events have transient or long-lasting effects on the environment. Stochastic events will give each planet a unique fingerprint. If life arises through abiogenesis of simple organic compounds (Des Marais, 1999 ; Popa, 2004 ; Shapiro, 2006 ; Pross, 2012 ; Pross and Pascal, 2013 ), this fingerprinting will be even more uniquely connected to its planet of origin, and cosmic chances are that both exogenic and endogenic processes are acting together in proportions specific to each planetary system.

Coevolution of life and environment. Environmental perception and neural systems of the species living on Earth are intimately linked to the coevolution of life and environment, a process that has been subjected to random probability events all along its continuum. This process started with accretion and the specific elements that contributed to planetary formation. As prebiotic chemistry transitioned to life, the period of heavy bombardment continued to spatially randomly deliver material to Earth, contributing equally to the destruction of a nascent life and the development of a new one. Since life took hold, stochastic events have continued in the physical world as environmental and cosmic catastrophes, and in the biological world as adaptive evolution and epigenetic changes. While the notions of habitable zone and environmental habitability are critical in trying to predict whether a planet could host life as we know it, the very random nature of the coevolution of life and environment renders each planet and the life it may bear a unique experiment, which questions the anthropocentric principle underlying the Drake equation.

Moreover, if Earth is any indication of universal planetary laws of evolution, nature produces simple systems in overwhelming numbers compared to complex systems (Mandelbrot, 1982 ). Statistically, microbial life still dominates today, and for 70% of Earth's history was the only form of life on our planet (Margulis, 1996 ; Nealson and Conrad, 1999 ; Wolf et al. , 2002 ). Taking inventory, global species richness estimates suggest that up to 10 million species of eukaryotes and up to 100 million to a billion prokaryote species exist today on Earth (Colwell and Coddington, 1994 ; Gaston, 2000 ; Colwell, 2009 ; Mora et al. , 2011 ; McGinley, 2014 ), while the most recent studies model up to one trillion species (Locey and Lennon, 2016 ). In this inventory of all terrestrial life, through competition, only humans have reached technology. However, this statistical snapshot alone does not provide an accurate estimate of a realistic ratio, as it does not reflect the (unknown) total number of species produced by our planet over time. Those include evolutionary dead ends and species that went extinct as a result of climatic or catastrophic events but still played their part in shaping the global biosphere from which we, the human species, emerged. It does not account for the shadow biosphere hypothesis, either (Cleland and Copley, 2005 ; Davies et al. , 2009 ).

A systemic approach to N shows that it took 4 billion years of symbioses, competition, biodiversification, and the development of all species that did—and did not—survive for us to be here. Some key evolutionary leaps have yet to be completely understood. Only very recently, the common ancestral gene that may have enabled the evolution of complex life over a billion years ago was identified. Without this gene, life on Earth might not have evolved beyond the stage of slime (Lai et al. , 2016 ). We also have yet to understand what led one species of apes to separate itself from the others just a few million years ago (Arsuaga, 2010 ). Understanding these transformative processes may bear considerable weight on N . It is certainly not necessary to wait for all the answers to start searching for ET, but we must acknowledge that these questions exist, and develop search strategies adapted to the complexity they underscore in order to augment the chances of success.

We are, indeed, the product of local astronomical and planetary factors. However, it would be unreasonable to suggest that similar evolutionary convergence never happened with seemingly so many planets already discovered in the small spatiotemporal window of the Kepler telescope. Somewhere out there, based solely on numbers and probabilities, life may have evolved to bear some resemblance to us—if only fortuitously. It might interact with its planetary environment as we do, and evolve to produce biological forms with logical minds presenting similarities to us who may be willing to communicate in ways we can understand. However, the numbers are unlikely to be in the billions or even the millions in our galaxy. There may be just a handful scattered across vast distances and time.

Taking life's evolution on Earth as a guide, there is likely a universal probabilistic law of evolutionary convergence that is inversely proportional to life's complexity; that is, the simpler life is, the greater chances are that similar life-forms will be abundant throughout the Universe. The more complex life is, the more rare convergence is likely to be. Complexity in life-forms is an integration of temporal evolution and probabilistic events. The longer life is around, the greater chance it has to adapt through regular cycles and, at any given time, to mutate through stochastic events. Looking back at ourselves, it took 70% of Earth's time in the habitable zone and an incredible amount of “chance and necessity” (Monod, 1972 ) for one species in a complex tree of life to reach civilization and technology.

The longer evolution takes, the greater the chances are that species will be wiped out and ecosystems profoundly transformed ( e.g. , Alvarez and Asaro, 1990 ), but with the rise of technology, some of the endogenic and exogenic risks to life can also be offset ( e.g. , asteroid monitoring, Yeomans, 2013 ). Conversely, human evolution shows that technology brings its own sets of risks: the natural dynamics are upset (Holocene extinction: Barnosky et al. , 2011 ), the environment modified (Anthropocene: Grinspoon, 2012 ; Waters et al. , 2016 ), and the terms of the coevolution of life and environment that led to the rise of the dominant species deeply altered.

At this point in time, humans have generated an environmental disequilibrium that reverberates across the biosphere globally and endangers the conditions of planetary habitability that were favorable to its emergence. The notion of self-engineered destruction is certainly present in the last factor of the Drake equation. L reflects on how long a technological civilization might be willing and able to communicate. More than duration, this factor focuses on the odds of detecting a signal; that is, the longer an alien civilization broadcasts its presence, the more chances we have to detect it. Assuming the anthropocentric view of a technological civilization presenting similarities with ours, willingness to communicate may depend on a host of reasons ( e.g. , political, scientific, technological, philosophical, religious, and social). How long such a civilization would continue to communicate is a more complex issue. Duration can relate to a civilization's ability to avoid self-inflicted—or other—destruction, scientific advances, and interest. It could also relate to a cosmologic perspective we have not yet reached, including a sense of place and responsibility as a member of a universal community ( e.g. , the Fermi paradox).

As expressed, L examines for how long such a civilization would broadcast a signal in ways we can detect, which are primarily focused on radio and optical astronomy. We could assume, however, that a technological civilization may communicate or broadcast in ways so advanced compared to ours that we simply cannot imagine what they are and are thus unable to detect its signals. Or this civilization may have long since disappeared. These scenarios are implicitly present in the current definition of L . However, there is also an evolutionary dimension to this factor that transcends the existing formulation.

5. Expanding the N Horizon

The evolutionary pathways that lead to complex life on Earth strongly suggest that advanced life as we know it may be rare in the Universe and unlikely to be in a state of advancement that is temporally synchronous with us. However, that does not mean that other types of advanced intelligences are as rare. Limiting our search to something we know and can de facto comprehend is, probabilistically, a constraining proposition, one that leaves no room for an epistemological and scientific foundation to explore alternate hypotheses. To find ET, we must expand our minds beyond a deeply rooted Earth-centric perspective and reevaluate concepts that are taken for granted .

5.1. Becoming aliens

Rather than constraining the search, SETI efforts must involve the most expansive exploration tool kit possible. If we unbind our minds, it should not matter whether ET looks or thinks like us, has a logic that makes any sense to us, or uses familiar technology for interstellar communication. ET is likely to be very different from us and completely alien to our evolutionary processes and thought processes, which may be deeply connected (see Section 5.2.3 ). Ultimately, to find aliens, we must become the aliens and understand the many ways they could manifest themselves in their environment and communicate their presence.

Such an intellectual framework not only moves the Drake equation forward toward the existence of drastically different probabilistic civilizations, it also brings us to consider alternate evolutionary pathways, including life as we do not know it and do not yet understand. Further, such a framework allows us to look at evolutionary pathways in our own biosphere and question the emergence of complex, intelligent life with a different set of eyes. For that to happen, we must conceptualize something we do not know, which can be approached in a number of different ways. One is by trying to access unknown concepts and archetypes that are literally alien to us ( i.e. , not part of our own evolutionary heritage) through imagination and discourse. This is what science fiction attempts to do in its depictions of alien worlds and civilizations. Not surprisingly, this process results in more or less elaborate versions of ourselves, since these representations are generated by neural systems wired to our own planetary environment. To conceptualize a different type of life, we have to step out of our brains.

5.2. Universal heritage

A path to finding life we do not know requires us to identify a common universal heritage , one that includes signatures and signals that can be recognized across different evolutionary tracks and across space and time. Research in this direction was initiated by the Communication with Extraterrestrial Intelligence (CETI) and the Arecibo message (Sagan, 1975 ; Vakoch, 2011a ). Advances in astrobiology, life science, and cognitive science are bringing new perspectives and depth to that concept. Some of them are already being explored, while others belong to disciplines that have yet to be involved with SETI and represent a currently untapped potential.

5.2.1. Distant biosignatures

In searching for life in the Solar System and on exoplanets, astrobiology is using an approach based on the concept of “universal heritage” but more narrowly focused on life as we know it (Seckbach, 2006 ). For instance, water and carbon are driving search strategies; the formation, preservation potential, and detection methods of biosignatures that could be similar to Earth's are being investigated for the exploration of extinct and extant life on Mars, Europa, and exoplanets. In situ biosignatures are physicochemical, geological, morphological, and mineralogical in nature (Summons et al. , 2011 ). Remotely detectable biosignatures include gases in planetary atmospheres (Pilcher, 2004 ; Segura et al. , 2005 ; Domagal-Goldman et al. , 2011 ; O'Malley-James et al. , 2014 ; Seager, 2014 ; Krissansen-Totton et al. , 2016 ). Given an environmental analogy, it is conceivable that alien biospheres presenting similarities with ours may have generated and left traces we could recognize. However, none of these signatures are convincingly unambiguous evidence of life's presence as both biological and abiotic processes alike can produce them (Schwieterman et al. , 2016 ). Therefore, it might be difficult to use them as universal markers of life as we know it, let alone for life we do not know.

Astrobiology and Earth sciences show that the systemic disequilibrium generated by the presence of life could be a promising candidate as a universal marker of life (Schwartzman, 2004 ; Branscomb and Russell, 2013 , Russell et al. , 2013 ). Biological activity, from microorganisms to humans, utilizes and modifies its environment, producing traces (physical, chemical, isotopic) not otherwise found in nature in the absence of life. As long as we search for biology with a physicochemical support, such disequilibrium will be generated and measurable across species and planets—although we will have to start by learning how to untangle it from the planetary background. The argument can also be made that some technological civilizations, or civilizations beyond technology, may be so advanced that they have returned to equilibrium and generate living conditions that do not betray their physical presence anymore—or they purposely hide their presence (Kipping and Teachey, 2016 ). In such instances, they will remain stealth to this search method. Planetary biosignatures reflecting the presence of a biosphere will still be visible, but traces of advanced beings on that planet may no longer be detectable.

While this marker falls short of helping the detection of environmentally stealthy civilizations, it can help find those that have not yet reached that stage. It also offers a universal vision to life detection that goes beyond life we know, thereby vastly expanding the statistical planetary pool that can be probed today. Further, and critical for SETI, this approach does not depend on the willingness of aliens to communicate. The coevolution of life and environment creates a physicochemical overprint that, regardless of the stage of life's development, will betray its presence. Learning the range of signatures produced by such disequilibrium from local to global scale should, therefore, become a priority in the development of techniques to search for life of all types, sizes, and advancement stages. Even though each candidate signature might not be produced by an advanced civilization, this method will identify more potential targets for SETI. The current limitation is both the spectral resolution of instruments and the distance of possible targets, but this method should become a critical investigation strategy to survey our galactic neighborhood (Seager and Deming, 2010 ; Deroo et al. , 2012 ; Beichman et al. , 2014 ; Burrows, 2014 ; Seager, 2014 ; Crossfield, 2015 ). A search for systemic disequilibria at a planetary scale is currently one of the most promising methods for detecting life beyond Earth. Taken alone, it might not be enough to inform us of the stages of life's development, but in the coming years, analog missions to our own atmosphere might teach us how to identify technosignatures.

5.2.2. Communication

Ultimately, the evidence SETI is looking for is an unambiguous signal from ET ( e.g. , Tarter, 1983 ; Shostak, 1998 ). To intercept alien signals, SETI has traditionally relied on radio astronomy for passive listening, and more recently on optical methods, and while the idea of active SETI—also known as Messaging Extraterrestrial Intelligence (METI)—remains a subject of controversy (Atri et al. , 2011 ; Vakoch, 2011b ; Vakoch and Matessa, 2011 ; Neal, 2014 ), communication and contact are very much at the core of the SETI concept. But what are we searching for and listening to?

In theory, SETI is searching for coded messages sent through controlled laser emissions or radio signals containing patterns that cannot be readily explained by known natural phenomena, ( e.g., Tarter, 2001b ; Vakoch, 2011a ; Forgan, 2014 ; Wheeler, 2014 ; Heller and Pudritz, 2016 ). Some research areas focus on the type of messages that should be broadcast if/when METI becomes active and on the content of these messages (Eliott, 2011b , 2011c ; Ollongren and Vakoch, 2011 ; Vakoch, 2011b , 2011c ; Musso, 2012 ). Since physical and mathematical principles are universal, they can be considered part of a universal heritage and a good starting point for composing messages (Ilhan and Linscott, 2011 ; Azua-Bustos and Vega-Martinez, 2013 ). Symbols, geometry, visual imageries, music, and sounds have been used in the past as part of the Pioneer and Voyager messages (Rose and Wright, 2004 ; Shostak, 2011b ). They continue to be investigated with the understanding that some might not be universal but biased toward senses humans have that ET might not have developed—or developed differently.

Since the ultimate goal of SETI is to identify alien signals, it should follow that understanding the origin, structures, and various forms and supports of communication (natural and artificial) is a fundamental step in the development and success of the search (Witzany, 2015 ). Research in marine and land species has already revealed common patterns that may be clues to laws of communication in the languages of some of Earth's intelligent species (Doyle et al. , 2011 ). This research area shows important promises, and these patterns might help us identify and decrypt alien messages coming our way one day. However, an important question—whose answer may lie in genomics and neuroscience—is whether these shared patterns are Earth-specific and the result of common environmental context and evolution, or actually universal in nature.

Further, perception and communication are severely constrained by sensory range ( e.g. , wavelengths, amplitude, reach) and by words in humans. The complexity and subtlety of a thought or a feeling can often be lost when it reaches verbal formulation even for members of the same cultural and linguistic groups. This limitation will be more acute between interplanetary species that evolved on planets with potentially different physicochemical conditions, environmental contexts, and mixings.

5.2.3. Environmental perception—alien neural systems

Most advanced alien species will likely have developed forms of communication completely unrecognizable to us. It can be hypothesized, however, that life anywhere must gather information about its environment for purposes of development, adaptation, survival, and evolution (Geary, 2005 ; Roth, 2013 ; Krubitzer, 2014 ; Schulkin, 2014 ). For terrestrial species, information is collected through senses, including many shared across species, while others are species-specific ( e.g. , echolocation, electroreception, magnetoreception). The senses are transducers from the environment to the brain where information is being interpreted—or through homolog systems for species without a nervous system (Strausfeld and Hirth, 2015 ). Alien life may need equivalent systems to process and integrate internal and external information. This is how ET will perceive its environment ( e.g. , Nolfi and Parisi, 1996 ; Pfeifer and Gómez, 2006 ) and communicate information about it in the messages it encodes, and for us, this is the key to unlock how we will decode them.

In that respect, cognitive and mathematical sciences ( e.g. , neuroscience, computational modeling, machine learning, other) may be the disciplines that can deliver the most transformative advances to SETI at this point in its history. By understanding how perception, concepts, and archetypes are being formed and formulated (Perlovsky, 2006 ) and how information is being stored and processed through neural or homolog systems, SETI could start exploring the source point of communication, where the elemental components of perceiving, interacting with, and communicating our understanding of planetary environments, our place in the Universe, and the Universe itself are being generated.

The structure and content of any alien message will have a local overtone to these elemental components driven by where (space and environment) and when (time) a civilization appeared in the Universe. However, on the cosmic scale, physics, chemistry, and biology are constrained by universal parameters that link all life —as diverse as it may be. These parameters are our common heritage and the letters of our universal alphabet. Life sciences, and cognitive and mathematical sciences, provide a fundamental and mandatory path for SETI to understand this universal alphabet. They are already used in the investigation of possible universal languages (Vakoch, 2011a ). However, in order to decode or encode messages from and to ET, a broader approach than the existing one is needed, one that considers the many possible combinations of evolutionary paths—not just those most familiar to us.

What SETI needs is a comprehensive integration of the concept of coevolution of life and environment in its search strategy, and the essential role it may play in the structure of ET's environmental sensing systems. That coevolution may fundamentally affect how aliens perceive their world, intellectualize it, and communicate it. As our knowledge of exoplanetary environments broadens, we are becoming better prepared to conceptualize the potential biochemistries and types of life these environments could support. We must use this background to develop probabilistic simulations of alien neural—or homolog sensing—systems. This will allow us to see the environment and the Universe as ET may perceive them, and not as we hope it does with our own set of senses. Without that basic understanding, SETI will essentially continue to search blind.

Such a research avenue can now find a robust scientific foundation in the advances made by evolutionary biology in innovative areas such as evolvability, evolutionary developmental biology, epigenomics, and system biology—regrouped under the term of extended synthesis (Pringle, 1951 ; Smith and Cribbs, 1994 ; Ziman, 2000 ; Wagner, 2007 ; Wagner et al. , 2007 ; Pigliucci and Müller, 2010 ; Wagner and Draghi, 2010 ; Schrey et al. , 2012 ; Jerison and Jerison, 2013 ; Valiant, 2013 ; Badyaev and Walsh, 2014 ; Watson and Szathmáry, 2015 ). This body of work strongly suggests that life, intelligence, and perception are shaped by, and designed to respond to, a planetary environment; this has powerful implications for SETI's anthropocentric principle and implications for its search strategy that cannot be ignored.

Today, vast amounts of data and computational capacity are at hand (Graham et al. , 2005 ; Heinecke et al. , 2015 ), allowing us to start on the path of modeling probabilistic evolutionary tracks using known exoplanetary environments, Solar System exploration, the exploration of extreme environments, and the computational tools of life, mathematical, and cognitive sciences and neuroscience ( e.g. , Wolpaw and Winter Wolpaw, 2012 ; Rao et al. , 2014 ). Results may lead us to first identify, then design, novel types of communication methods ( e.g. , message content and support), instruments, and technologies to search for ET.

Further, while evolutionary biology holds critical clues for our understanding of advanced intelligent life in the Universe, the implications of its applications to modeling alien life are much broader than SETI alone. As new theories mature through validation and falsification, they will help us interrogate more deeply the evolutionary continuum of intelligence on Earth from simple to complex life, a process highly relevant to astrobiology.

Ultimately, though, while understanding evolution, perception, and communication is absolutely essential to SETI, it will not be impactful if this knowledge remains compartmentalized. Data generated by each of these disciplines must be fused together and transformed into reasoned search strategies and experimental protocols. They must result in the identification and articulation of science questions and hypotheses that open pathways forward to theories and quantifiable metrics and milestones (see also Fig. 1 ).

6. An Integrated Vision Moving Forward

So far, a number of perspectives have been offered to explain why radio receivers have remained silent for the past 50 years, including the Fermi paradox and the Zoo hypothesis (Ball, 1973 ). More recently, two new scenarios have been added: ET is dead, based on the argument for a Gaian bottleneck (Chopra and Lineweaver, 2016 ), and the opposite view, that we are the oldest civilization in the Galaxy (Sasselov, 2012 ). It may be that the answer is much simpler and humbling. The fact is that we embarked on this journey only a few decades ago and have applied to it very limited tools and detection strategies. Telescopes have become bigger, arrays larger, resolution better, but the technology and exploration strategies behind SETI have remained basically unchanged. In reality, we have yet to articulate core questions to place SETI in its proper, systemic, and evolutionary context.

In its current scientific and technological form, SETI can be likened to sampling the cosmic ocean with a plankton net, where the size of the antennas and their number are analogous to the mesh size. Refining the mesh size by adding antennas or making them bigger will not make the tool more effective compared to the breadth of exploration at hand. Further, this tool is only focused toward testing one very specific, largely anthropocentric, hypothesis about extraterrestrial intelligence (ETI), when data increasingly suggest that there are probably as many distinct life-forms and intelligences as habitable planetary environments in the Universe. While the historical view of ETI is a valid hypothesis that must be tested, it is one among many, and we should proceed with it acknowledging that the chances of a rendezvous somewhere in time, and space, with that particular alien are remote.

When the odds are small and the object of a search unknown, the rule of thumb is to cast as large a net as possible to increase the chances of success rather than the opposite. In this case, a larger net is not solely a larger set of antennas or more abundant resources focused on one technology or one experiment (Billings, 2015 ). For SETI, it is critical to fully embrace the multidisciplinary approach that was scripted 50 years ago in the Drake equation and create a well-stocked and diverse tool kit to explore a vision that serves as an umbrella under which many disciplines will synergistically contribute advances to expand the search for alien life beyond the anthropocentric principle.

Some bridges are already in place and being investigated, such as the clear connections between the search for ET and exoplanet exploration ( e.g. , Tarter, 2007 ). SETI uses the Kepler catalog and ground-based telescope databases to target high-priority candidates. Prioritization criteria are currently limited to parameters for life as we know it ( e.g. , exoplanets in the habitable zone of their parent stars; unexplained signals from known exoplanetary systems, see Harp et al. , 2015 ; Schuetz et al. , 2015 ; Abeysekara et al. , 2016 ). Those criteria will be refined over time as universal markers are being identified and as we learn more about possible exotic biochemistries ( e.g. , McKay, 2004 ; Ward and Benner, 2007 ; Davila and McKay, 2014 ), but the connection is established and will only grow stronger.

In addition to this, new research pathways bear significant promises for a more universal SETI reach, such as ET and systemic planetary disequilibria, the coevolution of life and environment, and neural systems and their role in our perception of the Universe, our interaction with it and how we communicate about it—to name but a few. Figure 3 summarizes a path to achieving this integrated and synergistic vision. It shows a notional network between disciplines with bridges and research avenues connecting together space, planetary, life, geosciences, astrobiology, cognitive, and mathematical sciences. Others will be added as knowledge progresses. It is a dynamical vision forward, built on a connectivity network that represents an expanded version of the Drake equation, one that integrates all the historical factors now broken down into measurable terms.

Connectivity network between disciplines showing the bridges and research avenues that link together space, planetary, and life sciences, geosciences, astrobiology, and cognitive and mathematical sciences. This representation is an expanded version of the Drake equation. It integrates all the historical factors now broken down in measurable terms and expanded to include the search for life we do not know using universal markers, and the disciplines, fields, and methods that will allow us to quantify them.

This vision expands the search to life as we do not know it using universal markers and the disciplines, fields, and methods that will allow us to quantify them. Points of intersection are the knowledge that will be contributed to SETI by integrating these various disciplines. This contribution will be provided in five fundamental areas: (1) scientific rationale (theories, hypotheses); (2) experimental design (methods, protocols, and metrics); (3) communication (universal markers, signals, instruments, systems, technologies); (4) target identification; and (5) missions that will allow SETI to implement its own vision. These sciences are already collecting vast data sets that can now be interrogated in ways we could not have imagined only a few years ago. Bioneural computing, communication theory, machine learning, neural coding, neural network and deep learning, data mining, and big data analysis are the building blocks of the connecting bridges that SETI must build as a prerequisite to a universal exploration of ET versus the current anthropocentric search.

7. Conclusion

Now is the time for SETI to develop a roadmap and long-term vision that includes the search for life as we do not know it. New tools are available that can enable this approach and help us decipher the evolutionary and probabilistic nature of advanced alien life. These tools are found in astronomy and astrophysics but also in the biological, geological, cognitive, mathematical, and computer sciences, among others. All of them must be deployed when thinking about who, what, and where ET could be, and how it might communicate.

To find ET, we will have to turn inward (evolution, perception, and communication) and outward (planetary environments) and challenge our anthropocentric assumptions. Through consilience, we can build a systemic and connective vision of intelligent life in the Universe. To be achieved, this vision requires the exploitation of multidisciplinary synergies and an intellectual framework with a clear agenda and milestones. A similar intellectual and logistical structure was successfully established 20 years ago by NASA with the creation of the NASA Astrobiology Institute (NAI) for the understanding of life on Earth and beyond. However, past and present astrobiology roadmaps have not put substantial emphasis on alien intelligence, communication, or technology.

In the coming months, the SETI Institute will be initiating efforts in this direction, and will invite the United States and international research communities to contribute to the drafting of a new scientific roadmap for SETI. We will explore resources for the development of a virtual institute and an intellectual framework for multidisciplinary projects specifically focused on the advancement of knowledge on ETI. Complementary to, and different from, the astrobiology roadmap, this vision will bridge the NAI roadmap, augment it, and go beyond it.

Its primary goal will be to “Understand how intelligent life interacts with its environment and communicates.”

This will be explored through three main questions:

Question 1: How abundant and diverse is intelligent life in the Universe? With this question, SETI will synergistically use data from astrobiology, biological sciences, space and planetary science and exploration, and geoscience to quantitatively and qualitatively characterize the potential abundance and diversity of intelligent life in the Universe. Its spatiotemporal distribution will be approached using cosmological models of the physicochemical evolution of the Universe and inferred viable biochemistries.

Question 2: How does intelligent life communicate? Cognitive sciences, neuroscience, communication theory, mathematical sciences, bioneural computing, data mining, and big data analysis, among other disciplines, will explore communication in intelligent terrestrial species. They will use physicochemical and biochemical models of known exoplanetary environments to generate and map probabilistic neural and homolog systems, and infer the resulting range of viable alien sensing systems and the perception of the Universe they confer. Spatiotemporal distribution models will be inferred from Question 1–related investigations.

Question 3: How can we detect intelligent life? Exploration strategies, instruments, experimental protocols, technologies, and messaging (content and support) will be designed using the results, data, and databases of research conducted under Questions 1 and 2.

Ultimately, SETI's vision should no longer be constrained by whether ET has technology, resembles us, or thinks like us. The approach presented here will make these attributes less relevant, which will vastly expand the potential sampling pool and search methods, ultimately increasing the odds of detection.

Advanced, intelligent life beyond Earth is most likely plentiful, but we have not yet opened ourselves to the full potential of its diversity. With the vision presented here, we offer a unified and universal approach for the search for extraterrestrial life—one that is measurable and searches for ET at the crossroads of scientific and technological innovation, and imagination.

Abbreviations Used

Acknowledgments

I am particularly grateful to those who, through conversations, constructive criticism, suggestions, comments, and reviews at various stages of development have helped me articulate this perspective. Special thanks to Bill Diamond, David Darling, Margaret Race, Mark Showalter, and Jill Tarter for their inputs. Also thank you to Maggie Turnbull and Laurance Doyle for sharing thoughts over the past few months.

Author Disclosure Statement

The author declares no conflict of interest.

1 SETI in the context of this article means SETI research (as it is performed around the world) and should not be confused with the SETI Institute. In the cases where mention is made of the SETI Institute, this is clearly spelled out.

• Abeysekara A.U., Archambault S., Archer A., Bendow W., Bird R., Buchovecky M., Buckley J.H., Byrum K., Cardenzana J.V., Cerruti M., Chen X., Christiansen J.L., Ciupik L., Cui W., Dickinson H.J., Eisch J.D., Errando M., Falcone A., Furniss A., Gillanders G.H., Griffin S., Grube J., Gyuk G., Hütten M., Håkansson N., Hanna D., Holder J., Humensky T.B., Johnson C.A., Kaaret P., Kar P., Kelley-Hoskins N., Kertzman M., Kieda D., Krause M., Krennrich F., Kumar S., Lang M.J., Lin T.T.Y., Maier G., McArthur S., McCann A., Meagher K., Moriarty P., Mukherjee R., Nieto D., O'Brien S., O'Faoláin de Bhróithe A., Ong R.A., Otte A.N., Park N., Perkins J.S., Petrashyk A., Pohl M., Popkow A., Pueschel E., Quinn J., Ragan K., Ratliff G., Reynolds P.T., Richards G.T., Roache E., Santander M., Sembroski G.H., Shahinyan K., Staszak D., Telezhinsky I., Tucci J.V., Tyler J., Vincent S., Waleky S.P., Weiner O.M., Weinstein A., Williams D.A., and Zitzer B. (2016) A search for brief optical flashes associated with the SETI target KIC 8462852 . Astrophys J 818 , doi: 10.3847/2041-8205/818/2/L33 [ CrossRef ] [ Google Scholar ]
• Almár I. and Tarter J. (2011) The discovery of ETI as a high-consequence, low-probability event . Acta Astronaut 68 :358–361 [ Google Scholar ]
• Alvarez W. and Asaro F. (1990) An extraterrestrial impact: accumulating evidence suggests an asteroid or comet caused the Cretaceous extinction . Sci Am 263 :78–84 [ PubMed ] [ Google Scholar ]
• Ansbro E. (2001) New OSETI observatory to search for interstellar probes . Proc SPIE 4273, doi: 10.1117/12.435370 [ CrossRef ] [ Google Scholar ]
• Arrhenius G. and Mojzsis S. (1996) Extraterrestrial life: life on Mars—then and now . Curr Biol 6 :1213–1216 [ PubMed ] [ Google Scholar ]
• Arrhenius S. (1907) Panspermy: the transmission of life from star to star . Sci Am 96 :196 [ Google Scholar ]
• Arsuaga J.L. (2010) Terrestrial apes and phylogenetic trees . Proc Natl Acad Sci USA 107 :8910–8918 [ PMC free article ] [ PubMed ] [ Google Scholar ]
• Atri D., DeMarines J., and Haqq-Misra J. (2011) A protocol for messaging to extraterrestrial intelligence . Space Policy 27 :165–169 [ Google Scholar ]
• Azua-Bustos A. and Vega-Martinez C. (2013) The potential for detecting “life as we don't know it” by fractal complexity analysis . International Journal of Astrobiology 12 :314–320 [ Google Scholar ]
• Bada J.L., Bighamm C., and Miller S.L. (1994) Impact melting of frozen oceans on the early Earth—implications for the origin of life . Proc Natl Acad Sci USA 91 :1248–1250 [ PMC free article ] [ PubMed ] [ Google Scholar ]
• Badyaev A.V. and Walsh J.B. (2014) Epigenetic processes and genetic architecture . In Quantitative Genetics in the Wild , edited by Charmantier W.A., Garant D., and Kruuk L.E.B., Oxford University Press, Oxford, UK, pp 177–189 [ Google Scholar ]
• Ball J.A. (1973) The zoo hypothesis . Icarus 19 :347–349 [ Google Scholar ]
• Barnosky A.D., Matzke N., Tomiya S., Wogan G.O.U., Swartz B., Quental T.B., Marshall C., McGuire J.L., Lindsey E.L., Maguire K.C., Mersey B., and Ferrer E.A. (2011) Has the Earth's sixth mass extinction already arrived? Nature 471 :51–57 [ PubMed ] [ Google Scholar ]
• Batalha N.M. (2014) Exploring exoplanet populations with NASA's Kepler mission . Proc Natl Acad Sci USA 111 :12647–12654 [ PMC free article ] [ PubMed ] [ Google Scholar ]
• Beichman C., Benneke B., Knutson H., Smith R. D.ressing C., Latham D., Deming D., Lunine J., Lagage P.-O., Sozzetti A., Sing D., Kempton E., Ricker G., Bean J., Kreiberg L., Bouwman J., Crossfield I., Christiansen J., Ciardi D., Fortney J., Albert L., Doyon R., Rieke M., Rieke G., Clampin M., Greenhouse M., Goudfrooij P., Hines D., Keyes T., Lee J., McCullough P., Robberto M., Stansberry J., Valenti J., Deroo P.D., Mandell A., Ressler M.E., Shporer A., Swain M., Vasisht G., Carey S., Krick J., Birkmann S., Ferruit P., Giardino G., Greene T., and Howell S. (2014) Observations of transiting exoplanets with the James Webb Space Telescope (JWST) . Publ Astron Soc Pac 126 :1134–1173 [ Google Scholar ]
• Bijlsma R., Westerhof M.D.D., Roekx L.P., and Pen I. (2013) Dynamics of genetic rescue in inbred Drosophila melanogaster populations . Conserv Genet 111 :449–462 [ Google Scholar ]
• Billingham J., Edelson R., Gulkis S., Olsen E.T., Oliver B.M., Tarter J.C., and Seeger C.L. (1980) A search strategy for SETI [paper #IAA-80-57] . In 9 th International CETI Review Meeting of the International Academy of Astronautics, Tokyo, Japan [ Google Scholar ]
• Billings L. (2015, July 20) Stephen Hawking and Yuri Milner announce $100M initiative to seek ET . Sci Am [ Google Scholar ]
• Borucki W.J., Koch D., Basri G., Batalha N., Brown T., Caldwell D., Caldwell J., Christensen-Dalsgaard J., Cochran W.D., DeVore E., Dunham E.W., Dupree A.K., Gautier T.N., Geary J.C., Gilliland R., Gould R., Howell S.B., Jenkins J., Kondo Y., Latham D.W., Marcy G.W., Mejbom S., Kjeldsen H., Lissauer J.J., Monet D.G., Morrison D., Sasselov D., Tarter J., Boss A., Brownlee D., Owen T., Buzasi D., Charbonneau D., Doyle L., Fortney J., Ford E.B., Holman M.J., Seager S., Steffen J.H., Welsh W.F., Rowe J., Anderson H., Buchhave L., Ciardi D., Walkowicz L., Sherry W., Horch E., Isaacson H., Everett M.E., Fisher D., Torres G., Johnson J.A., Endl M., MacQueen P., Bryson S.T., Dotson J., Haas M., Kolodziejczak J., Van Cleve J., Chandrasekaran H., Twicken J.D., Quintana E.V., Clarke B.D., Allen C., Lie J., Wu H., Tenembaum P., Verner E., Bruhweiler F., Barnes J., and Prsa A. (2010) Kepler planet-detection mission: introduction and first results . Science 327 :977–980 [ PubMed ] [ Google Scholar ]
• Brack A. (2005) From the origin of life on Earth to life in the Universe . In Lectures in Astrobiology , Vol. 1 , edited by Gargaud M., Springer, Berlin, pp 3–21 [ Google Scholar ]
• Branscomb E. and Russell M.J. (2013) Turnstiles and bifurcators: the disequilibrium converting engines that put metabolism on the road . Biochim Biophys Acta 1827 :62–78 [ PubMed ] [ Google Scholar ]
• Burchell M.J., Mann J.R., and Bunch A.W. (2004) Survival of bacteria and spores under extreme pressures . Mon Not R Astron Soc 352 :1273–1278 [ Google Scholar ]
• Bürger R. and Lynch M. (1995) Evolution and extinction in a changing environment: a quantitative-genetic analysis . Evolution 49 :151–163 [ PubMed ] [ Google Scholar ]
• Burrows A.S. (2014) Highlights in the study of exoplanet atmospheres . Nature 513 :345–352 [ PubMed ] [ Google Scholar ]
• Chopra A. and Lineweaver C.H. (2016) The case for a Gaian bottleneck: the biology of habitability . Astrobiology 16 :7–22 [ PubMed ] [ Google Scholar ]
• Cleland C.E. and Copley S.D. (2005) The possibility of alternative microbial life on Earth . International Journal of Astrobiology 4 :165–173 [ Google Scholar ]
• Cocconi G. and Morrison P. (1959) Searching for interstellar communications . Nature 184 :844–846 [ Google Scholar ]
• Cockell C.S., Bush T., Bryce C., Direito S., Fox-Powell M., Harrison J.P., Lammer H., Landenmark H., Martin-Torres J., Nicholson N., Noack L., O'Malley-James J., Payler S.J., Rushby A., Samuels T., Schwendner P., Wadsworth J., and Zorzano M.P. (2016) Habitability: a review . Astrobiology 16 :89–117 [ PubMed ] [ Google Scholar ]
• Colwell R.K. (2009) Biodiversity: concepts, patterns and measurement . In The Princeton Guide to Ecology , edited by Levin S.A., Princeton University Press, Princeton, NJ, pp 257–263 [ Google Scholar ]
• Colwell R.K. and Coddington J.A. (1994) Estimating terrestrial biodiversity through extrapolation . Philos Trans R Soc Lond B Biol Sci 345 :101–118 [ PubMed ] [ Google Scholar ]
• Cowan J.J. and Sneden C. (2006) Heavy element synthesis in the oldest stars and early universe . Nature 440 :1151–1156 [ PubMed ] [ Google Scholar ]
• Crossfield I.J.M. (2015) Observations of exoplanet atmospheres . Publ Astron Soc Pac 127 :941–960 [ Google Scholar ]
• Crowe M.J. (2011) The Extraterrestrial Life Debate, 1750–1900 , Dover Publications, Mineola, NY [ Google Scholar ]
• Darling D. and Schulze-Makuch D. (2016) The Extraterrestrial Encyclopedia , First Edition Design Publishing, Sarasota, FL [ Google Scholar ]
• Davies P.C., Benner S.A., Cleland C.E., Lineweaver C.H., McKay C.P., and Wolfe-Simon F. (2009) Signatures of the shadow biosphere . Astrobiology 9 :241–291 [ PubMed ] [ Google Scholar ]
• Davila A.F. and McKay C.P. (2014) Chance and necessity in biochemistry: implications for the search of extraterrestrial biomarkers in Earth-like environments . Astrobiology 14 :534–540 [ PMC free article ] [ PubMed ] [ Google Scholar ]
• de Fontenelle B.B. (1686) Entretiens sur la Pluralité des Mondes , Nouvelle Edition augmentée (1701), Pierre Mortier, Librairie fur le Vygen-Dam, Amsterdam [ Google Scholar ]
• Deroo P., Swain M.R., and Green O. (2012) Spectroscopy of exoplanet atmospheres with the FINESSE Explorer mission . Proc SPIE 8442 , doi: 10.1117/12.925236 [ CrossRef ] [ Google Scholar ]
• Des Marais D.J. (1999) Astrobiology: exploring the origins, evolution, and distribution of life in the Universe . Annu Rev Ecol Syst 30 :397–420 [ PubMed ] [ Google Scholar ]
• Des Marais D.J., Nuth J.A., III, Allamandola L.J., Boss A.P., Farmer J.D., Hoehler T.M., Jakosky B.M., Meadows V.S., Pohorille A., Runnegar B., and Spormann A.M. (2008) The NASA Astrobiology Roadmap . Astrobiology 8 :715–730 [ PubMed ] [ Google Scholar ]
• Descartes R. (1644) Principia Philosophiae , apud Ludovicum Elzevirum, Ghent University, Belgium [ Google Scholar ]
• Dick S.J. (1984) Plurality of Worlds: The Origins of the Extraterrestrial Life Debate from Democritus to Kant , Cambridge University Press, Cambridge, UK [ Google Scholar ]
• Dietrich L.E.P, Michael M., and Newman D.K. (2006) The co-evolution of life and Earth . Curr Biol 16 :pR395–pR400 [ PubMed ] [ Google Scholar ]
• Domagal-Goldman S.D., Meadows V.S., Claire M.W., and Kasting J.F. (2011) Using biogenic sulfur gases as remotely detectable biosignatures on anoxic planets . Astrobiology 11 :419–441 [ PMC free article ] [ PubMed ] [ Google Scholar ]
• Doyle L.R., McCowan B., Johnston S., and Hanser S.F. (2011) Information theory, animal communication, and the search for extraterrestrial intelligence . Acta Astronaut , SETI Special Edition, 68 :406–417 [ Google Scholar ]
• Drake F. (2011) The search for extra-terrestrial intelligence . Philos Trans A Math Phys Eng Sci 369 :633–643 [ PubMed ] [ Google Scholar ]
• Dyson F.J. (1999) Origins of Life , 2 nd ed., Cambridge University Press, Cambridge, UK [ Google Scholar ]
• Eliott J. (2011a) A human language corpus for interstellar message construction . Acta Astronaut , SETI Special Edition, 68 :418–424 [ Google Scholar ]
• Eliott J. (2011b) A semantic “engine” for universal translation . Acta Astronaut , SETI Special Edition, 68 :435–440 [ Google Scholar ]
• Eliott J. (2011c) A post-detection decipherment strategy . Acta Astronaut , SETI Special Edition, 68 :441–444 [ Google Scholar ]
• Fabbro F., Aglioti S.M., Bergamasco M., Clarici A., and Panksepp J. (2015) Evolutionary aspects of self- and world consciousness in vertebrates . Front Hum Neurosci 9 , doi: 10.3389/fnhum.2015.00157 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Fitz D., Reiner H., and Rode B.M. (2007) Chemical evolution toward the origin of life . Pure Appl Chem 79 :2101–2117 [ Google Scholar ]
• Flammarion C. (1872) La Pluralité des Mondes Habités , Didier, Paris [ Google Scholar ]
• Forgan D.H. (2014) Can collimated extraterrestrial signals be intercepted? J Br Interplanet Soc 67 :232–236 [ Google Scholar ]
• Gaidos E., Anderson D.R., Lepine S., Colon K.D., Maravelias G., Narita N., Chang E., Beyer J., Fukui A., Armstrong J.D., Zezas A., Fulton B.J., Mann A.W., West R.G., and Faedi F. (2014) Trawling for transits in a sea of noise: a search for exoplanets by analysis of WASP optical light curves and follow-up (SEAWOLF) . Mon Not R Astron Soc 437 :3133–3143 [ Google Scholar ]
• Garber S.J. (1999) Searching for good science: the cancellation of NASA's SETI Program . J Br Interplanet Soc 52 :3–12 [ Google Scholar ]
• Gaston K.J. (2000) Global patterns in biodiversity . Nature 405 :220–227 [ PubMed ] [ Google Scholar ]
• Geary D.C. (2005) The Origin of the Mind: Evolution of Brain, Cognition, and General Intelligence , 1 st ed., American Psychological Association, Washington, DC [ Google Scholar ]
• Gibb B.C. (2013) Life, the Universe and nomenclature . Nat Chem 5 , doi: 10.1038/nchem.1530 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Gladman B., Dones L., Levison H.F., and Burns J.A. (2005) Impact seeding and reseeding in the inner Solar System . Astrobiology 5 :483–496 [ PubMed ] [ Google Scholar ]
• Golding S.D. and Glikson M. (2011) Earliest Life on Earth: Habitats, Environments and Methods of Detection , Springer, Dordrecht, the Netherlands [ Google Scholar ]
• Gould S.J. (1998) Evolution and Extinction , Audio Scholar, Mendocino, CA [ Google Scholar ]
• Graham S.L., Snir M., and Patterson C.A., editors. (2005) The Future of Supercomputing , The National Academies Press, Washington, DC [ Google Scholar ]
• Grazier K.R. (2016) Jupiter: cosmic Jekyll and Hyde . Astrobiology 16 :23–38 [ PubMed ] [ Google Scholar ]
• Grenfell J.L., Rauer H., Selsis F., Kaltenegger L., Beichman C., Danchi W., Eiroa C., Fridlund M., Henning T., Herbst T., Lammer H., Léger A., Lisaeu R., Lunine J., Paresce F., Penny A., Quirrenbach A., Röttgering H., Schneider J., Stam D., Tinetti G., and White G.J. (2010) Co-evolution of atmospheres, life, and climate . Astrobiology 10 :77–88 [ PubMed ] [ Google Scholar ]
• Grinspoon D.H. (2012) Assessing the Anthropocene in the context of comparative planetology [abstract #P14A-02] . In American Geophysical Union, Fall Meeting 2012 , American Geophysical Union, Washington, DC [ Google Scholar ]
• Gulkis S., Olsen E.T., and Tarter J.C. (1981) A bimodal search strategy for SETI . In Strategies for the Search for Life in the Universe , edited by Papagiannis M.D., D. Reidel Publishing Co., Dordrecht, the Netherlands, pp 93–105 [ Google Scholar ]
• Harp G.R., Richards J., Shostak S., Tarter J.C., Vakoch D.A., and Munson C. (2015) Radio SETI observations of the anomalous star KIC 8462852 . arXiv:1511.01606
• Hatzes A.P. (2014) The detection of Earth-mass planets around active stars: the mass of Kepler-78B . Astron Astrophys 568 , doi: 10.1051/0004-6361/201424025 [ CrossRef ] [ Google Scholar ]
• Heath M.J., Doyle L.R., Joshi M.J., and Haberle R. (1998) Habitability of planets around red dwarf stars . Orig Life Evol Biosph 29 :405–424 [ PubMed ] [ Google Scholar ]
• Heinecke A., Eckhardt W., Horsch M., and Bungartz H.-J. (2015) Supercomputing for Molecular Dynamics Simulations: Handling Multi-Trillion Particles in Nanofluidics , Springer Briefs in Computer Science, Springer International Publishing, Cham, Switzerland [ Google Scholar ]
• Heller R. and Pudritz R.E. (2016) The search for extraterrestrial intelligence in Earth's solar transit zone . Astrobiology 16 :259–270 [ PubMed ] [ Google Scholar ]
• Heller R., Leconte J., and Barnes R. (2011) Tidal obliquity evolution of potentially habitable planets . Astron Astrophys 528 , doi: 10.1051/0004-6361/201015809 [ CrossRef ] [ Google Scholar ]
• Horner J., Waltham D., and Koch F.E. (2013) The role of Jupiter in driving Earth's orbital evolution . In Proceedings of the 13 th Australian Space Science Conference, Sept. 30–Oct. 2, 2013 [ Google Scholar ]
• Houri-Ze'evi L., Korem Y., Sheftel H., Faigenbloom L., Toker I.A., Dagan Y., Awad L., Degani L., Alon U., and Rechavi O. (2016) A tunable mechanism determines the duration of the transgenerational small RNA inheritance in C. elegans . Cell 165 :88–99 [ PubMed ] [ Google Scholar ]
• Ilhan H. and Linscott I. (2011) Using fractal derivatives as “degree of symmetry” to characterize natural shapes . Acta Astronaut , SETI Special Edition, 68 :425–434 [ Google Scholar ]
• Imari Walker S. (2014) Transition from abiotic to biotic: is there an algorithm for it? In An Evolutionary Approach , edited by Kolb V., CRC Press, Boca Raton, FL, pp 371–398 [ Google Scholar ]
• Irwin N.I. and Schulze-Makuch D. (2001) Assessing the plausibility of life on other worlds . Astrobiology 1 :143–160 [ PubMed ] [ Google Scholar ]
• Irwin N.I., Méndez A., Fairén A.G., and Schulze-Makuch D. (2014) Assessing the possibility of biological complexity on other worlds, with an estimate of the occurrence of complex life in the Milky Way Galaxy . Challenges 5 :159–174 [ Google Scholar ]
• Jerison H.J. and Jerison I. (2013) Intelligence and Evolutionary Biology , NATO ASI Series G, Ecological Sciences, Vol. 17 Springler-Verlag, Berlin [ Google Scholar ]
• Kant I. (2009) Universal Natural History and Theory of the Heavens , Translated by Johnston I.C., Richer Resources Publications, Arlington, VA: (Original work published in 1755) [ Google Scholar ]
• Kasting J.F. (1993) Earth's earliest atmosphere . Science 259 :920–926 [ PubMed ] [ Google Scholar ]
• Keller G. and Kerr A. (2014) Volcanism, Impacts, and Mass Extinctions: Causes and Effects , GSA Special Paper 505, Geological Society of America, Boulder, CO [ Google Scholar ]
• Kipping D.M. and Teachey A. (2016) A cloaking device for transiting planets . Mon Not R Astron Soc 458 , doi: 10.1093/mnras/stw672 [ CrossRef ] [ Google Scholar ]
• Knoll A.H. (2009) The co-evolution of life and environments . Rendiconti Lincei Scienze Fisiche e Naturali 20 :301–306 [ Google Scholar ]
• Kolb V. (2014) Astrobiology: An Evolutionary Approach , CRC Press, Boca Raton, FL [ Google Scholar ]
• Kooijman S.A.L.M. (2004) On the co-evolution of life and its environment . In Scientists Debate Gaia: The Next Century , edited by Schneider S.H., Miller J.R., Crist E., and Boston P.J., MIT Press Scholarship Online, Cambridge, MA, doi: 10.7551/mitpress/9780262194983.003.0032 [ CrossRef ] [ Google Scholar ]
• Kopparapu R., Ravi K., Ramirez R., Kasting J.F., Eymet V., Robinson T.D., Mahadevan S., Terrien R., Ryan C., Domagal-Goldman S., Meadows V., and Deshpande R. (2013) Habitable zones around main sequence stars: new estimates . Astrophys J 765 , doi: 10.1088/0004-637X/765/2/131 [ CrossRef ] [ Google Scholar ]
• Krissansen-Totton J., Bergsman D.S., and Catling D.C. (2016) On detecting biospheres from chemical thermodynamic disequilibrium in planetary atmospheres . Astrobiology 16 :39–67 [ PubMed ] [ Google Scholar ]
• Krubitzer L. (2014) Lessons from evolution . In The Future of the Brain: Essays by the World's Leading Neuroscientists , edited by Marcus G. and Freeman J., Princeton University Press, Princeton, NJ, pp 186–193 [ Google Scholar ]
• Lai S., Safaei J., and Pelech S. (2016) Evolutionary ancestry of eukaryotic protein kinases and choline kinases . J Biol Chem 291 :5199–5205 [ PMC free article ] [ PubMed ] [ Google Scholar ]
• Laskar J., Joutel F., and Robutel P. (1993) Stabilization of the Earth's obliquity by the Moon . Nature 361 :615–617 [ Google Scholar ]
• Lazcano A. and Miller S.L. (1996) The origin and early evolution of life: prebiotic chemistry, the pre-RNA world, and time . Cell 85 :793–798 [ PubMed ] [ Google Scholar ]
• Lehman J. and Miikkulainen R. (2015) Extinction events can accelerate evolution . PLoS One 10 , doi: 10.1371/journal.pone.0132886 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Lissauer J.J., Barnes J.W., and Chambers J.E. (2011) Obliquity variations of a moonless Earth . Icarus 217 :77–87 [ Google Scholar ]
• Locey K.J. and Lennon J.T. (2016) Scaling laws predict global microbial diversity . Proc Natl Acad Sci USA 113 :5970–5975 [ PMC free article ] [ PubMed ] [ Google Scholar ]
• Lowell P. (1906) Mars and Its Canals , Macmillan Company, New York [ Google Scholar ]
• Lynch M. and Lande R. (1993) Evolution and extinction in response to environmental change . In Biotic Interactions and Global Change , edited by Kingsolver J.G. and Huey R.B., Sinauer, Sunderland, MA [ Google Scholar ]
• Lyons T.W., Reinhard C.T., and Planavsky N.J. (2014) The rise of oxygen in Earth's early ocean and atmosphere . Nature 506 :307–315 [ PubMed ] [ Google Scholar ]
• Maccone C. (2012) Mathematical SETI: Statistics, Signal Processing, Space Missions , Springer-Verlag, Berlin [ Google Scholar ]
• Macintosh B., Graham J.R., Barman T., De Rosa R.J., Konopacky Q., Marley M.S., Marois C., Nielsen E.L, Pueyo L., Rajan A., Rameau J., Saumon D., Wang J.J., Ammons M., Arriaga P., Artigau E., Beckwith S., Brewster J., Bruzzone S., Bulger J., Burningham B., Burrow A.S., Chen C., Chiang E., Chilcote J.K., Dawson R.I., Dong R., Doyon R., Draper Z.H., Duchêne G., Esposito T.M., Fabrycky D., Fitzgerald M.P., Follette K.B., Fortney J.J., Gerard B., Goodsell S., Greenbaum A.Z., Hibon P., Hinkley S., Cotton T.H., Hung L.-W., Ingraham P., Johnson-Groh M., Kalas P., Lafreniere D., Larkin J.E., Lee J., Line M., Long D., Maire J., Marchis F., Matthews B.C., Max C.E., Metchev S., Millar-Blanchaer M.A., Mittal T., Morley C.V., Morzinskim K.M., Murray-Clay R., Oppenheimer R., Palmer D.W., Patel R., Patience J., Perrin M.D., Poyneer L.A., Rafikov R.R., Rantakyrö F.T., Rice E., Rojo P., Rudy A.R., Ruffio J.-B., Ruiz M.T., Sadakuni N., Saddlemyer L., Salama M., Savransky D., Schneider A.C., Sivaramakrishnan A., Song I., Soummer R., Thomas S., Vasisht G., Wallace J.K., Ward-Duong K., Wiktorowicz S.J., Wollff S.G., and Zuckerman B. (2015) Discovery and spectroscopy of the young jovian planet 51 Eri b with the Gemini Planet Imager . Science 350 :64–67 [ PubMed ] [ Google Scholar ]
• Mandelbrot B.B. (1982) The Fractal Geometry of Nature , W.H. Freeman and Company, San Francisco [ Google Scholar ]
• Mandell A.V.(2008) Expanding and improving the search for habitable worlds . In New Horizons in Astronomy: Frank N. Bash Symposium 2007, ASP Conference Series Vol. 393 , Astronomical Society of the Pacific, San Francisco, pp 19–34 [ Google Scholar ]
• Margulis L. (1996) Archaeal-eubacterial mergers in the origin of Eukarya: phylogenetic classification of life . Proc Natl Acad Sci USA 93 :1071–1076 [ PMC free article ] [ PubMed ] [ Google Scholar ]
• Martin W., Baross J., Kelley D., and Russel M. (2008) Hydrothermal vents and the origin of life . Nat Rev 6 :805–814 [ PubMed ] [ Google Scholar ]
• McCollom T.M. (2013) Miller-Urey and beyond: what have we learned about prebiotic organic synthesis reactions in the past 60 years? Annu Rev Earth Planet Sci 41 :207–229 [ Google Scholar ]
• McGinley M. (2014) Species richness . In The Encyclopedia of Earth (EoE) . Retrieved from http://www.eoearth.org/view/article/156216
• McKay C.P. (2004) What is life—and how do we search for it in other worlds? PLoS Biol 2 , doi: 10.1371/journal.pbio.0020302 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Melosh J. (1996) Impact Cratering: A Geologic Process , Oxford Monographs on Geology and Geophysics no. 11, Oxford University Press, New York [ Google Scholar ]
• Monod J. (1972) Chance and Necessity: An Essay on the Natural Philosophy of Modern Biology , Vintage Books, New York [ Google Scholar ]
• Mora C., Tittensor D.P., Adl S., Simpson A.G.B., and Worm B. (2011) How many species are there on Earth and in the ocean? PLoS Biol 9 , doi: 10.1371/journal.pbio.1001127 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Musso P. (2012) The problem of active SETI: an overview . Acta Astronaut 78 :43–54 [ Google Scholar ]
• Napier W.M. (2004) A mechanism for interstellar panspermia . Mon Not R Astron Soc 348 :46–51 [ Google Scholar ]
• Neal M. (2014) Preparing for extraterrestrial contact . Risk Management 16 :63–87 [ Google Scholar ]
• Nealson K.H. and Conrad P.G. (1999) Life: past, present and future . Philos Trans R Soc Lond B Biol Sci 354 :1923–1939 [ PMC free article ] [ PubMed ] [ Google Scholar ]
• Nolfi S. and Parisi D. (1996) Learning to adapt to changing environments in evolving neural networks . Adapt Behav 5 :75–98 [ Google Scholar ]
• Ollongren A. and Vakoch D.A. (2011) Large-size message construction for ETI: logical existence expressed in Lingua Cosmica . In SETI Science and Technology Review Meeting, 62 nd International Astronautical Congress, Cape Town, South Africa [ Google Scholar ]
• O'Malley-James J.T., Cockell C.S., Greaves J.S., and Raven J.A. (2014) Swansong biospheres II: The final signs of life on terrestrial planets near the end of their habitable lifetimes . International Journal of Astrobiology 13 :229–243 [ Google Scholar ]
• Owen T. (2008) The contributions of comets to planets, atmospheres, and life: insights from Cassini-Huygens, Galileo, Giotto, and inner planet missions . Origin and Early Evolution of Comet Nuclei: Workshop Honouring Johannes Geiss on the Occasion of His 80 th Birthday, Space sciences series of ISSI, Vol. 28 , Springer, New York, pp 301–316 [ Google Scholar ]
• Pascal R., Boiteau L., Forterre P., Gargaud M., Lazcano A., López-García P., Moreira D., Maurel M.-C., Peretó J., Prieur D., and Reisse J. (2006) Prebiotic chemistry—biochemistry—emergence of life (4.4–2 Ga) . Earth Moon Planets 98 :153–203 [ Google Scholar ]
• Perlovsky L.I. (2006) Toward physics of the mind: concepts, emotions, consciousness, and symbols . Phys Life Rev 3 :23–55 [ Google Scholar ]
• Petigura E.A., Howard A.W., and Marcy G.W. (2013) Prevalence of Earth-size planets orbiting Sun-like stars . Proc Natl Acad Sci USA 110 :19273–19278 [ PMC free article ] [ PubMed ] [ Google Scholar ]
• Pfeifer R. and Gómez G. (2006) Morphological computation—connecting brain, body, and environment . In Creating Brain-Like Intelligence , Lecture Notes in Computer Science 5436, edited by Sendhoff B., Springer, Berlin, pp 66–83 [ Google Scholar ]
• Pigliucci M. and Müller G.B., editors. (2010) Evolution, the Extended Synthesis , MIT Press, Cambridge, MA [ Google Scholar ]
• Pilcher C.B. (2004) Biosignatures of early Earths . Astrobiology 3 :471–486 [ PubMed ] [ Google Scholar ]
• Popa R. (2004) Between Necessity and Probability: Searching for the Definition and Origin of Life , Springer, Berlin [ Google Scholar ]
• Pringle J.W.S. (1951) On the parallel between learning and evolution . Behaviour 3 :174–214 [ Google Scholar ]
• Pross A. (2012) What Is Life? How Chemistry Becomes Biology , Oxford University Press, Oxford, UK [ Google Scholar ]
• Pross A. and Pascal R. (2013) The origin of life: what we know, what we can know, and what we will never know . Open Biology 3 , doi: 10.1098/rsob.120190 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Quintana E.V., Barclay T., Raumond S.N., Rowe J.F., Bolmont E., Caldwell D.A., Howell S.B., Kane S.R., Huber D., Crepp J.R., Lissauer J.J., Ciardi D.R., Coughlin J.L., Everett M.E., Henze C.E., Horch E., Isaacson H., Ford E.B., Adams F.C., Still M., Hunter R.C., Quarles B., and Selsis F. (2014) An Earth-sized planet in the habitable zone of a cool star . Science 344 :277–280 [ PubMed ] [ Google Scholar ]
• Rao R.P.N., Stocco A., Bryan M., Sarma D., and Youngquist T.M. (2014) A direct brain-to-brain interface in humans . PLoS One 9 , doi: 10.1371/journal.pone.0111332 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Raup D.M. (1999) The role of extinction in evolution . Proc Natl Acad Sci USA 91 :6758–6763 [ PMC free article ] [ PubMed ] [ Google Scholar ]
• Rose C. and Wright G. (2004) Inscribed matter as an energy-efficient means of communication with an extraterrestrial civilization . Nature 431 :47–49 [ PubMed ] [ Google Scholar ]
• Rosenfeld S. (2011) Mathematical descriptions of biochemical networks: stability, stochasticity, evolution . Prog Biophys Mol Biol 106 :400–409 [ PMC free article ] [ PubMed ] [ Google Scholar ]
• Roth G. (2013) The Long Evolution of Brains and Minds , Springer, Dordrecht, the Netherlands [ Google Scholar ]
• Ruiz-Mirazo K., Brionest C., and de la Escosura A. (2013) Prebiotic systems chemistry: new perspectives on the origins of life . Chem Rev 114 :285–366 [ PubMed ] [ Google Scholar ]
• Russell M.J., Nitschke W., and Branscomb E. (2013) The inevitable journey to being . Philos Trans R Soc Lond B Biol Sci 368 , doi: 10.1098/rstb.2012.0254 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Sagan C. (1975) Communication with Extraterrestrial Intelligence , MIT Press, Cambridge, MA [ Google Scholar ]
• Sasselov D. (2012) The Life of Super-Earths: How the Hunt for Alien Worlds and Artificial Cells Will Revolutionize Life on our Planet , Basic Books, New York [ Google Scholar ]
• Schrey A.W., Richards C.L., Meller V., Sollars V., and Ruden D.M. (2012) The role of epigenetics in evolution: the extended synthesis . Genet Res Int 2012 , doi: 10.1155/2012/286164 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Schuch H.P. (2011) Project Ozma: the birth of observational SETI . In Searching for Extraterrestrial Intelligence , The Frontiers Collection, Springer, Berlin, pp 13–19 [ Google Scholar ]
• Schuetz M., Vakoch D.A., Shostak S., and Richards J. (2015) Optical SETI observations of the anomalous star KIC 8462852 . arXiv:1512.02388
• Schulkin J. (2014) Cognitive Adaptation: A Pragmatist Perspective , Cambridge University Press, Cambridge, UK [ Google Scholar ]
• Schulze-Makuch D. and Irwin L.N. (2001) Lessons from the history of life on Earth . In Life in the Universe , edited by Schulze-Makuch D. and Irwin L.N., Advances in Astrobiology and Biogeophysics, Springer, Berlin, pp 25–41 [ Google Scholar ]
• Schulze-Makuch D., Irwin L.N., and Fairén A.G. (2013) Drastic environmental change and its effects on a planetary biosphere . Icarus 225 :775–780 [ Google Scholar ]
• Schwartz R.N. and Townes C.H. (1961) Interstellar and interplanetary communication by optical masers . Nature 190 :205–208 [ Google Scholar ]
• Schwartzman D.W. (2004) Does life drive disequilibrium in the biosphere? In Scientists Debate Gaia: The Next Century , edited by Schneider S.H., Miller J.R., Crist E., and Boston P.J., MIT Press, Cambridge, MA, doi: 10.7551/mitpress/9780262194983.003.0013 [ CrossRef ] [ Google Scholar ]
• Schwieterman E.W., Meadows V.S., Domagal-Goldman S.D., Deming D., Arney G.N., Luger R., Harman C.E., Misra A., and Barnes R. (2016) Identifying planetary biosignature impostors: spectral features of CO and O 4 resulting from abiotic O 2 /O 3 production . Astrophys J 819 , doi: 10.3847/2041-8205/819/1/L13 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Seager S. (2013) Exoplanet habitability . Science 340 :577–581 [ PubMed ] [ Google Scholar ]
• Seager S. (2014) The future of spectroscopic life detection on exoplanets . Proc Natl Acad Sci USA 11 :12634–12640 [ PMC free article ] [ PubMed ] [ Google Scholar ]
• Seager S. and Deming D. (2010) Exoplanet atmospheres . Annu Rev Astron Astrophys 48 :631–672 [ Google Scholar ]
• Seckbach J., editor. (2006) Life as We Know It , Cellular Origin and Life in Extreme Habitats and Astrobiology, Vol. 10 , Springer, Dordrecht, the Netherlands [ Google Scholar ]
• Seckbach J., Chela-Flores J., Owen T., andRaulin F., editors. (2004) Life in the Universe: From the Miller Experiment to the Search for Life on Other Worlds , Cellular Origin and Life in Extreme Habitats and Astrobiology, Vol. 7 , Springer, Dordrecht, the Netherlands [ Google Scholar ]
• Segura A., Kasting J.F., Meadows V., Cohen M., Scalo J., Crisp D., Butler R.A.H., and Tinetti G. (2005) Biosignatures from Earth-like planets around M dwarfs . Astrobiology 5 :706–725 [ PubMed ] [ Google Scholar ]
• Seifer M.J. (1996) Martian fever (1895–1896) . In Wizard: The Life and Times of Nikola Tesla: Biography of a Genius , Carol Publishing Group, Secaucus, NJ [ Google Scholar ]
• Shapiro R. (2006) Small molecule interactions were central to the origin of life . Q Rev Biol 81 :105–125 [ PubMed ] [ Google Scholar ]
• Shostak S. (1998) Sharing the Universe: Perspectives on Extraterrestrial Life , Berkeley Hills Book, Berkeley, CA [ Google Scholar ]
• Shostak S. (2011a) Short-pulse SETI . Acta Astronaut , SETI Special Edition, 68 :362–365 [ Google Scholar ]
• Shostak S. (2011b) Limits on interstellar messages . Acta Astronaut , SETI Special Edition, 68 :366–371 [ Google Scholar ]
• Smith R.E. and Cribbs H.B., III, editors. (1994) Evolutionary Computation , MIT Press, Cambridge, MA [ Google Scholar ]
• Spohn T. (1991) Mantle differentiation and thermal evolution of Mars, Mercury, and Venus . Icarus 90 :222–236 [ Google Scholar ]
• Stern R.J. (2015) Is plate tectonics needed to evolve technological species on exoplanets? Geoscience Frontiers 7 :573–580 [ Google Scholar ]
• Strausfeld N.J. and Hirth F. (2015) Introduction to “Homology and convergence in nervous system evolution.” Philos Trans R Soc Lond B Biol Sci 317, doi: 10.1098/rstb.2015.0034 [ PMC free article ] [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Summons R.E., Amend J.P., Bish D., Buik R., Cody G.D., Des Marais D.J., Dromart G., Eigenbrode J.L., Knoll A.H., and Sumner D.Y. (2011) Preservation of martian organic and environmental records: final report of the Mars Biosignature Working Group . Astrobiology 11 :157–181 [ PubMed ] [ Google Scholar ]
• Swendenborg E. (1758) Life on Other Planets , 1 st ed., Swedenborg Foundation, West Chester, PA [ Google Scholar ]
• Tarter J.C. (1979) The Cosmic Haystack , Harlan Smith Working Group on SETI of the National Academy of Sciences Astronomy and Astrophysics for the 1980s Survey Committee [ Google Scholar ]
• Tarter J.C. (1983) SETI Program . Letter to Science 22 :359 [ PubMed ] [ Google Scholar ]
• Tarter J.C. (2001a) The search for extraterrestrial intelligence (SETI) . Annu Rev Astron Astrophys 39 :511–548 [ Google Scholar ]
• Tarter J.C. (2001b) What is SETI? Ann NY Acad Sci 950 :269–275 [ PubMed ] [ Google Scholar ]
• Tarter J.C. (2004) Astrobiology and SETI . New Astronomy Reviews 48 :1543–1549 [ Google Scholar ]
• Tarter J.C. (2007) The evolution of life in the Universe: are we alone? Proceedings of the International Astronomical Union 2 :14–29 [ Google Scholar ]
• Tarter J.C. and Chyba C.F. (1999) Is there life elsewhere in the Universe? Sci Am 281 :80–85 [ Google Scholar ]
• Tarter J.C., Backus P., Mancinelli R., Aurnou J., Backman D., Basri G., Boss A., Clarke A., Deming D., Doyle L., Feigelson E., Freund F., Grinspoon D., Haberle R., Hauck S., Heath M., Henry T., Hollingsworth J., Joshi M., Jura M., Kilston S., Laughlin G., Liu E., Meikle M., Reid I., Rothschild L., Scalo J., Segura A., Tang C., Tiedje J., Turnbull M., Walkowicz L., Weber A., and Young R. (2007) A reappraisal of the habitability of planets around M dwarf stars . Astrobiology 7 :30–65 [ PubMed ] [ Google Scholar ]
• Turnbull M.C. and Tarter J.C. (2003) Target selection for SETI. I. A catalog of nearby habitable stellar systems . Astrophys J Suppl Ser 145 :181–198 [ Google Scholar ]
• Vakoch D.A., editor. (2011a) Communication with Extraterrestrial Intelligence , State University of New York Press, Albany, NY [ Google Scholar ]
• Vakoch D.A. (2011b) A taxonomic approach to communicating maxims in interstellar messages . Acta Astronaut , SETI Special Edition, 68 :500–511 [ Google Scholar ]
• Vakoch D.A. (2011c) A narratological approach to interpreting and designing interstellar messages . Acta Astronaut , SETI Special Edition, 68 :520–534 [ Google Scholar ]
• Vakoch D.A., editor. (2014) Between Worlds: The Art and Science of Interstellar Message Composition , MIT Press, Cambridge, MA [ Google Scholar ]
• Vakoch D.A. and Dowd M.F. (2015) The Drake Equation: Estimating the Prevalence of Extraterrestrial Life through the Ages , Cambridge Astrobiology Series Book 8, Cambridge University Press, Cambridge, UK [ Google Scholar ]
• Vakoch D.A. and Harrison A.H., editors. (2011) Civilization beyond Earth: Extraterrestrial Life and Society , Berghahn Books, New York [ Google Scholar ]
• Vakoch D.A. and Matessa M. (2011) An algorithmic approach to communicating reciprocal altruism in interstellar messages: drawing analogies between social and astrophysical phenomena . Acta Astronaut , SETI Special Edition, 68 :459–475 [ Google Scholar ]
• Valiant L. (2013) Probably Approximately Correct: Nature's Algorithms for Learning and Prospering in a Complex World , Basic Books, New York [ Google Scholar ]
• Voltaire F.-M.A. (2002) Micromégas and Other Short Fictions , translated by Cuffe T. and Mason H.T., Penguin Classics, New York. (Original work published in 1752) [ Google Scholar ]
• Wagner A. (2007) Robustness and Evolvability in Living Systems , Princeton University Press, Princeton, NJ [ Google Scholar ]
• Wagner G.P. and Draghi J. (2010) Evolution of evolvability . In Evolution: The Extended Synthesis , edited by Pigliucci M. and Müller G.B., MIT Press, Cambridge, MA, pp 218–228 [ Google Scholar ]
• Wagner G.P., Pavlicev M., and Cheverud J.M. (2007) The road to modularity . Nat Rev Genet 8 :921–931 [ PubMed ] [ Google Scholar ]
• Walker S.I. (2014) Top-down causation and the rise of information in the emergence of life . Information 5 :424–439 [ Google Scholar ]
• Ward P.D. and Benner S.A. (2007) Alien biochemistries . In Planets and Life: The Emerging Science of Astrobiology , edited by Sullivan W.T., III and Baross J.A., Cambridge University Press, Cambridge, UK, pp 537–544 [ Google Scholar ]
• Ward P.D. and Brownlee D. (2003) Rare Earth: Why Complex Life is Uncommon in the Universe , Copernicus Books, New York [ Google Scholar ]
• Waters C.N., Zalasiewicz J., Summerhayes C., Barnosky A.D., Poirier C., Galuszka A., Cearreta A., Edgeworth M., Ellis E.C., Ellis M., Jeandel C., Leindfelder R., McNeill J.R., deB. Richter D., Steffen W., Syvitski J., Vids D., Wagreich M., Williams M., Grinevald J., Odada E., Oreskes N., and Wolfe A.P. (2016) The Anthropocene is functionally and stratigraphically distinct from the Holocene . Science 351 , doi: 10.1126/science.aad2622 [ PubMed ] [ CrossRef ] [ Google Scholar ]
• Watson A.J. (1999) Coevolution of the Earth's environment and life: Goldilocks, Gaia and the anthropic principle . Geol Soc Spec Publ 150 :75–88 [ Google Scholar ]
• Watson R.A. and Szathmáry E. (2015) How can evolution learn? Trends Ecol Evol 31 :147–157 [ PubMed ] [ Google Scholar ]
• Wheeler E. (2014) The “Wow” signal, Drake equation, and exoplanet considerations . J Br Interplanet Soc 67 :412–417 [ Google Scholar ]
• Witzany G. (2015) Life is physics and chemistry and communication . Ann NY Acad Sci 1341 :1–9 [ PubMed ] [ Google Scholar ]
• Wolf Y.I., Rogozin I.B., Grishin N.V., and Koonin E.V. (2002) Genome trees and the tree of life . Trends Genet 18 :472–479 [ PubMed ] [ Google Scholar ]
• Wolpaw J.R. and Winter Wolpaw E., editors. (2012) Brain-Computer Interfaces: Principles and Practice , Oxford University Press, Oxford, UK [ Google Scholar ]
• Worth R.J., Sigurdsson S., and House C.H. (2013) Seeding life on the moons of the outer planets via lithopanspermia . Astrobiology 13 :1155–1165 [ PMC free article ] [ PubMed ] [ Google Scholar ]
• Wright S.A., Werthimer D., Treffers R.R., Maire J., Marcy G.W., Stone R.P.S., Drake F., Meyer E., Dorval P., and Siemon A. (2014) A near-infrared SETI experiment: instrument overview . Proc SPIE 9147 , doi: 10.1117/12.2055616 [ CrossRef ] [ Google Scholar ]
• Yeomans D.K. (2013) Near-Earth Objects: Finding Them Before They Find Us , Princeton University Press, Princeton, NJ [ Google Scholar ]
• Zackrisson E., Calissendorff P., González J., Benson A., Johansen A., and Janson M. (2016) Terrestrial planets across space and time . arXiv:1602.00690 [ Google Scholar ]
• Ziman J., editor. (2000) Technological Innovation as an Evolutionary Process , Cambridge University Press, Cambridge, UK [ Google Scholar ]
• Zuckerman B. and Tarter J.C. (1979) Is there anyone out there? Nature 281 :528–529 [ Google Scholar ]

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

• View all journals
• Explore content
• About the journal
• Publish with us
• Sign up for alerts
• NEWS EXPLAINER
• 30 January 2023

Will an AI be the first to discover alien life?

• Alexandra Witze

You can also search for this author in PubMed   Google Scholar

From the hills of West Virginia to the flats of rural Australia, some of the world’s largest telescopes are listening for signals from distant alien civilizations. The search for extraterrestrial intelligence, known as SETI, is an effort to find artificial-looking electromagnetic-radiation signals that might have come from a technologically advanced civilization in a far-away solar system. A study published today 1 describes one of several efforts to use machine learning, a subset of artificial intelligence (AI), to help astronomers sift quickly through the reams of data such surveys yield. As AI reshapes many scientific fields , what promise does it hold for the search for life beyond Earth?

Access options

Access Nature and 54 other Nature Portfolio journals

Get Nature+, our best-value online-access subscription

24,99 € / 30 days

cancel any time

Subscribe to this journal

Receive 51 print issues and online access

185,98 € per year

only 3,65 € per issue

Rent or buy this article

Prices vary by article type

Prices may be subject to local taxes which are calculated during checkout

Nature 614 , 208 (2023)

doi: https://doi.org/10.1038/d41586-023-00258-z

Ma, P. X. et al. Nature Astron . https://doi.org/10.1038/s41550-022-01872-z (2023).

Article   Google Scholar  

Download references

Reprints and permissions

Related Articles

Director for Signature Research Programme in Cancer and Stem Cell Biology, DukeNUS Medical School &

The successful candidate will demonstrate their ability of growing, leading and mentoring faculty as well as developing and operationalising strategy.

Singapore (SG)

DukeNUS Medical School

Scientist / Postdoc (m/f/d): Analysis of Microscopic BIOMedical Images (AMBIOM)

A new project area in the institute is the development of artificial intelligence (AI)

Dortmund, Nordrhein-Westfalen (DE)

Leibniz-Institut für Analytische Wissenschaften – ISAS – e.V.

PhD Candidate (m/f/d): Analysis of Microscopic BIOMedical Images (AMBIOM)

Senior researcher-experimental leukemia modeling, mullighan lab.

Memphis, Tennessee

St. Jude Children's Research Hospital (St. Jude)

Assistant or Associate Professor (Research-Educator)

The Center for Molecular Medicine and Genetics in the Wayne State University School of Medicine (http://genetics.wayne.edu/) is expanding its high-...

Detroit, Michigan

Wayne State University

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Quick links

• Explore articles by subject
• Guide to authors
• Editorial policies

Harvard professor leading research on existence of UFOs and alien civilizations

Some of our questions about the existence of UFOs and extraterrestrial civilizations could be answered by a new international research project led by Harvard University.

The Galileo Project , led by Harvard astronomy professor Avi Loeb, will search for a record of alien civilizations capable of technology surpassing what we know on Earth. It will use telescope observations, missions that send cameras into space and more..

"Given the recently discovered abundance of Earth-Sun systems, the Galileo Project is dedicated to the proposition that humans can no longer ignore the possible existence of Extraterrestrial Technological Civilizations (ETCs)," the team said in a statement . 

The project comes on the heels of the government's report on Unidentified Aerial Phenomena and an interstellar object, Oumuamua, that entered our solar system in 2017 as reasons to search and confirm the presence of ETCs.

Harvard researchers: Mysterious interstellar object floating in space might be alien

Loeb told USA TODAY that the idea for the project is that "in the future, we will find more objects from interstellar space, and those that look peculiar we should follow up by sending a camera on a space rocket that gets close to them and taking a close-up photograph."

He added that the project will allow scientists to take a further look into unidentified objects in space after the government's report was released last month. 

"Those military personnel and politicians that talk about these Unidentified Aerial Phenomena were not trained by scientists, and it's sort of like asking the plumber to bake you a cake," Loeb told USA TODAY. "We should not ask them to figure out what objects in the sky are all about. That’s the job of scientists." 

The team, which includes professors from Princeton, Cambridge and Stockholm universities, will study existing and future astronomical surveys along with artificial intelligence to identify interstellar objects that defy current scientific explanations. 

The data collected will be available to the public, and the team said the process would be transparent. 

Loeb noted that the project may not find groundbreaking evidence on interstellar objects, but he explained that the research will still help scientists understand other "atmospheric phenomena." 

"It's just like a fishing expedition," he said. "You don't know what you will find, and I don't want to make any assumptions." 

But he still called the project "one of the most fascinating questions that science can address." 

"It will have huge implications on society, on humanity," Loeb said. "If we find evidence for a smarter kid on our cosmic block, it will change the way we think about our place in the universe, our relations with each other," he said.

"If we close the shutters on our windows and say ‘We don't have neighbors. We are the smartest, and give me extraordinary evidence before I will be willing to look through my window,’ then we will maintain our ignorance, just like in the days of Galileo."

'Important first step': Highly anticipated UFO report released with no firm conclusions

Aliens watching us?  Thousands of star systems can see Earth, new report says.

Follow reporter Asha Gilbert @Coastalasha. Email: [email protected].

Follow reporter Marina Pitofsky @marina_pitofsky. Email: [email protected]

• Skip to main content
• Keyboard shortcuts for audio player

NASA is looking for a framework to better help you understand its deep space finds

Joe Hernandez

The moon shines over radio antennas at the operations support facility of one of the worlds largest astronomy projects, the Atacama Large Millimeter/submillimeter Array (ALMA), in the Atacama desert in northern Chile in this 2012 photo. Jorge Saenz/AP hide caption

The moon shines over radio antennas at the operations support facility of one of the worlds largest astronomy projects, the Atacama Large Millimeter/submillimeter Array (ALMA), in the Atacama desert in northern Chile in this 2012 photo.

Is there life on other planets? It's a simple question without a simple answer.

"The expectation, in particular with the public, is a yes-or-no answer. Did you find it or didn't you find it?" Jim Green, NASA's chief scientist, told NPR.

But Green says the reality is much more complex. One scientific discovery about extraterrestrial life may give us a small new insight into the universe, but it may be exaggerated by researchers or misunderstood by the public.

The discovery of the meteorite ALH 84001 — which ignited excitement about the possibility of life on Mars — is one example from history.

Strange News

Ufo report: no sign of aliens, but 143 mystery objects defy explanation.

Green walks us through another example. Say a scientist is looking at a distant exoplanet roughly the size of Earth, roughly the same distance from a star, with oxygen and clouds in its atmosphere. That means vegetation on the surface of the planet may be generating the oxygen in the atmosphere, and it's possible we've just found life outside our solar system!

"Well, I got news for you, we know that planet, and that planet is Venus," Green said. "We see oxygen in the atmosphere of Venus, and I can guarantee there is no vegetation on the surface of Venus. So that one observation, although it sounded great, doesn't give us the confidence to lean forward and say we found life or could have found life."

Just because a planet could support life doesn't mean it ever has or will.

"That extrapolation may have absolutely no basis in the science that they've done," he said, referring to researchers, "and potentially could mislead the community into saying we have found life or we're closer to finding life without a really good scale as to how far away that really is."

Scientists tracked a mysterious signal in space. Its source was closer to Australia

That's why Green and NASA are proposing a scale to better contextualize new findings in research about extraterrestrial life and help explain those discoveries to the public.

In an article in Nature , Green and other NASA scientists propose a seven-step rubric for understanding new discoveries. It starts with the remote detection of something that could hint at life and progresses to ruling out non-biological factors, making actual observations and finally conducting follow-up observations to be sure that life exists.

If NASA greenlights this interstellar mission, it could last 100 years

The scientists say their scale is just a proposal, and they're looking for the scientific community to weigh in and improve it.

According to the article, an objective standard is needed now because the current generation of scientists may be the one to discover life beyond Earth.

"Without the scale, it's hard to tell we're making progress, we're going in the right direction," Green said.

Suggested Searches

• Climate Change
• Expedition 64
• Mars perseverance
• SpaceX Crew-2
• International Space Station
• View All Topics A-Z

Humans in Space

Earth & climate, the solar system, the universe, aeronautics, learning resources, news & events.

FAQ: NASA’s Boeing Crew Flight Test Return Status

NASA’s EXCITE Mission Prepared for Scientific Balloon Flight

Talented Teams Tackle Toasty Planet

• Search All NASA Missions
• A to Z List of Missions
• Upcoming Launches and Landings
• Spaceships and Rockets
• Communicating with Missions
• James Webb Space Telescope
• Hubble Space Telescope
• Why Go to Space
• Commercial Space
• Destinations
• Living in Space
• Explore Earth Science
• Earth, Our Planet
• Earth Science in Action
• Earth Multimedia
• Earth Science Researchers
• Pluto & Dwarf Planets
• Asteroids, Comets & Meteors
• The Kuiper Belt
• The Oort Cloud
• Skywatching
• The Search for Life in the Universe
• Black Holes
• The Big Bang
• Dark Energy & Dark Matter
• Earth Science
• Planetary Science
• Astrophysics & Space Science
• The Sun & Heliophysics
• Biological & Physical Sciences
• Lunar Science
• Citizen Science
• Astromaterials
• Aeronautics Research
• Human Space Travel Research
• Science in the Air
• NASA Aircraft
• Flight Innovation
• Supersonic Flight
• Air Traffic Solutions
• Green Aviation Tech
• Drones & You
• Technology Transfer & Spinoffs
• Space Travel Technology
• Technology Living in Space
• Manufacturing and Materials
• Science Instruments
• For Kids and Students
• For Educators
• For Colleges and Universities
• For Professionals
• Science for Everyone
• Requests for Exhibits, Artifacts, or Speakers
• STEM Engagement at NASA
• NASA's Impacts
• Centers and Facilities
• Directorates
• Organizations
• People of NASA
• Internships
• Our History
• Doing Business with NASA
• Get Involved

NASA en Español

• Aeronáutica
• Ciencias Terrestres
• Sistema Solar
• All NASA News
• Video Series on NASA+
• Newsletters
• Social Media
• Media Resources
• Upcoming Launches & Landings
• Virtual Events
• Image of the Day
• Sounds and Ringtones
• Interactives
• STEM Multimedia

Hubble Reaches a Lonely Light in the Dark

NASA Funds Studies to Support Crew Performance on Long-Duration Missions

NextSTEP R: Lunar Logistics and Mobility Studies

Station Science Top News: August 16, 2024

STV Precursor Coincident Datasets

NASA-Designed Greenhouse Gas-Detection Instrument Launches

Airborne Surface, Cryosphere, Ecosystem, and Nearshore Topography

The Making of Our Alien Earth: The Undersea Volcanoes of Santorini, Greece

NASA Shares Asteroid Bennu Sample in Exchange with JAXA

Gateway: Energizing Exploration

Hubble Finds Structure in an Unstructured Galaxy

NASA Composite Manufacturing Initiative Gains Two New Members

Beyond the Textbook: DC-8 Aircraft Inspires Students in Retirement

NASA Celebrates Ames’s Legacy of Research on National Aviation Day

Copernicus Trajectory Design and Optimization System

Perseverance Pays Off for Student Challenge Winners

How Do I Navigate NASA Learning Resources and Opportunities?

Preguntas frecuentes: estado del retorno de la prueba de vuelo tripulado boeing de la nasa.

Astronauta de la NASA Frank Rubio

Diez maneras en que los estudiantes pueden prepararse para ser astronautas

Nasa research gives guideline for future alien life search.

William Steigerwald

Astronomers searching the atmospheres of alien worlds for gases that might be produced by life can’t rely on the detection of just one type, such as oxygen, ozone, or methane, because in some cases these gases can be produced non-biologically, according to extensive simulations by researchers in the NASA Astrobiology Institute’s Virtual Planetary Laboratory. 

The researchers carefully simulated the atmospheric chemistry of alien worlds devoid of life thousands of times over a period of more than four years, varying the atmospheric compositions and star types. “When we ran these calculations, we found that in some cases, there was a significant amount of ozone that built up in the atmosphere, despite there not being any oxygen flowing into the atmosphere,” said Shawn Domagal-Goldman of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “This has important implications for our future plans to look for life beyond Earth.”

Methane is a carbon atom bound to four hydrogen atoms. On Earth, much of it is produced biologically (flatulent cows are a classic example), but it can also be made inorganically; for example, volcanoes at the bottom of the ocean can release the gas after it is produced by reactions of rocks with seawater.

Ozone and oxygen were previously thought to be stronger biosignatures on their own. Ozone is three atoms of oxygen bound together. On Earth, it is produced when molecular oxygen (two oxygen atoms) and atomic oxygen (a single oxygen atom) combine, after the atomic oxygen is created by other reactions powered by sunlight or lightning. Life is the dominant source of the molecular oxygen on our planet, as the gas is produced by photosynthesis in plants and microscopic, single-cell organisms. Because life dominates the production of oxygen, and oxygen is needed for ozone, both gases were thought to be relatively strong biosignatures. But this study demonstrated that both molecular oxygen and ozone can be made without life when ultraviolet light breaks apart carbon dioxide (a carbon atom bound to two oxygen atoms). Their research suggests this non-biological process could create enough ozone for it to be detectable across space, so the detection of ozone by itself would not be a definitive sign of life.

“However, our research strengthens the argument that methane and oxygen together, or methane and ozone together, are still strong signatures of life,” said Domagal-Goldman. “We tried really, really hard to make false-positive signals for life, and we did find some, but only for oxygen, ozone, or methane by themselves.” Domagal-Goldman and Antígona Segura from the Universidad Nacional Autónoma de México in Mexico City are lead authors of a paper about this research, along with astronomer Victoria Meadows, geologist Mark Claire, and Tyler Robison, an expert on what Earth would look like as an extrasolar planet. The paper appeared in the Astrophysical Journal Sept. 10, and is available online.

Methane and oxygen molecules together are a reliable sign of biological activity because methane doesn’t last long in an atmosphere containing oxygen-bearing molecules. “It’s like college students and pizza,” says Domagal-Goldman. “If you see pizza in a room, and there are also college students in that room, chances are the pizza was freshly delivered, because the students will quickly eat the pizza. The same goes for methane and oxygen. If both are seen together in an atmosphere, the methane was freshly delivered because the oxygen will be part of a network of reactions that will consume the methane. You know the methane is being replenished. The best way to replenish methane in the presence of oxygen is with life. The opposite is true, as well. In order to keep the oxygen around in an atmosphere that has a lot of methane, you have to replenish the oxygen, and the best way to do that is with life.”

Scientists have used computer models to simulate the atmospheric chemistry on planets beyond our solar system (exoplanets) before, and the team used a similar model in its research. However, the researchers also developed a program to automatically compute the calculations thousands of times, so they could see the results with a wider range of atmospheric compositions and star types.

In doing these simulations, the team made sure they balanced the reactions that could put oxygen molecules in the atmosphere with the reactions that might remove them from the atmosphere. For example, oxygen can react with iron on the surface of a planet to make iron oxides; this is what gives most red rocks their color. A similar process has colored the dust on Mars, giving the Red Planet its distinctive hue. Calculating the appearance of a balanced atmosphere is important because this balance would allow the atmosphere to persist for geological time scales. Given that planetary lifetimes are measured in billions of years, it’s unlikely astronomers will happen by chance to be observing a planet during a temporary surge of oxygen or methane lasting just thousands or even millions of years.

It was important to make the calculations for a wide variety of cases, because the non-biological production of oxygen is subject to both the atmospheric and stellar environment of the planet. If there are a lot of gases that consume oxygen, such as methane or hydrogen, then any oxygen or ozone produced will be destroyed in the atmosphere. However, if the amount of oxygen-consuming gases is vanishingly small, the oxygen and the ozone might stick around for a while. Likewise, the production and destruction of oxygen, ozone, and methane is driven by chemical reactions powered by light, making the type of star important to consider as well. Different types of stars produce the majority of their light at specific colors. For example, massive, hot stars or stars with frequent explosive activity produce more ultraviolet light. “If there is more ultraviolet light hitting the atmosphere, it will drive these photochemical reactions more efficiently,” said Domagal-Goldman. “More specifically, different colors (or wavelengths) of ultraviolet light can affect oxygen and ozone production and destruction in different ways.”

Astronomers detect molecules in exoplanet atmospheres by measuring the colors of light from the star the exoplanet is orbiting. As this light passes through the exoplanet’s atmosphere, some of it is absorbed by atmospheric molecules. Different molecules absorb different colors of light, so astronomers use these absorption features as unique “signatures” of the type and quantity of molecules present.

“One of the main challenges in identifying life signatures is to distinguish between the products of life and those compounds generated by geological processes or chemical reactions in the atmosphere. For that we need to understand not only how life may change a planet but how planets work and the characteristics of the stars that host such worlds”, said Segura.

The team plans to use this research to make recommendations about the requirements for future space telescopes designed to search exoplanet atmospheres for signs of alien life. “Context is key – we can’t just look for oxygen, ozone, or methane alone,” says Domagal-Goldman. “To confirm life is making oxygen or ozone, you need to expand your wavelength range to include methane absorption features. Ideally, you’d also measure other gases like carbon dioxide and carbon monoxide [a molecule with one carbon atom and one oxygen atom]. So we’re thinking very carefully about the issues that could trip us up and give a false-positive signal, and the good news is by identifying them, we can create a good path to avoid the issues false positives could cause. We now know which measurements we need to make. The next step is figuring out what we need to build and how to build it.”

The research was funded in part by the NASA Astrobiology Institute’s (NAI) Virtual Planetary Laboratory (VPL). The NAI is administered by NASA’s Ames Research Center in Mountain View, California, and funded as part of the NASA Astrobiology Program at NASA Headquarters, Washington. The VPL is based at the University of Washington, and comprises researchers at 20 institutions working to understand how telescopic observations and modeling studies can determine if exoplanets are able to support life, or had life in the past. Additional support for the research was provided by the NASA Postdoctoral Program, managed by Oak Ridge Associated Universities.

The team represented an international collaboration that included researchers from NASA Goddard, NASA Ames, the NAI/VPL, the Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Mexico; the University of St. Andrews, St. Andrews, Scotland; and the University of Washington, Seattle.

For more information about the NASA Astrobiology Institute, visit:

http://astrobiology.nasa.gov/

The research paper is available online at:

http://stacks.iop.org/0004-637X/792/90

William Steigerwald NASA’s Goddard Space Flight Center , Greenbelt, Maryland

Gabriela Frias Universidad Nacional Autonoma de Mexico , Mexico City

Top of page

Collection Finding Our Place in the Cosmos: From Galileo to Sagan and Beyond

Ufos and aliens among us.

In the 1940s and 50s reports of "flying saucers" became an American cultural phenomena. Sightings of strange objects in the sky became the raw materials for Hollywood to present visions of potential threats. Posters for films, like Earth vs. the Flying Saucers from 1956 illustrate these fears.  Connected to ongoing ideas about life on the Moon, the canals on Mars, and ideas about Martian Civilizations, flying saucers have come to represent the hopes and fears of the modern world.

Are these alleged visitors from other worlds peaceful and benevolent or would they attack and destroy humanity? The destructive power of the Atomic bomb called into question the progressive potential of technology . Fear of the possibilities for destruction in the Cold War-era proved fertile ground for terrestrial anxieties to manifest visions of flying saucers and visitors from other worlds who might be hidden among us in plain sight.

Aliens Among us and Fears of the Other

If UFOs were visiting our world, where were these extraterrestrials? Could they be hidden among us? Comic books and television illustrates how the possibility of extraterrestrial visitors reflected anxieties of that era.

The 1962 comic There are Martians Among Us , from Amazing Fantasy #15, illustrates the way fear of extraterrestrials could reflect Cold War anxieties. In the comic, a search party gathers around a landed alien craft, but it can find no sign of alien beings. Radio announcers warn those nearby to stay indoors. The action shifts to a husband and wife as he prepares to leave their home despite a television announcer's warning to remain indoors. As he waves goodbye he reminds his wife to stay inside. The wife however decides to slip out to the store and is attacked and dragged off. The husband returns home and finding it empty runs towards the telephone in a panic. In a twist, the anxious husband reveals that he and his wife are the Martians.

The fear that there might be alien enemies in our midst resonates with fears of Soviets and communists from the McCarthy era. Ultimately, in this story, the humans are the ones who accost and capture the alien woman. The shift in perspective puts the humans in the position of the monsters.

UFOs as Contemporary Folklore

Aside from depictions of UFOs in media, UFOs are also part of American folk culture. Ideas of aliens and flying saucers are a part of the mythology of America. You can find documentation of these kinds of experiences in folk life collections. An interview with Howard Miller about hunting and hound dogs, collected as part of Tending the Commons: Folklife and Landscape in Southern West Virginia collection, documents an individual's experience with a potential UFO sighting.

In A mysterious light , a segment of an ethnographic interview, Miller describes a strange light he saw once while hunting with his dogs in 1966 "All at once it was daylight, and I looked up to see what happened. There was a light about that big, going up, drifting up the hill. When I looked and seen it just faded out. I've been in the Marines, and know what airplane lights look like, and it was too big for that." When asked if he knew what it was he offered, "I don't know what it was" but went on to explain, "If there is any such thing as a UFO that's what that was." This unexplained light on a walk in the woods is typical of many stories of these kinds of encounters. It's not only the media that tells stories and represents these kinds of ideas, documentation of the experiences and stories Americans tell each other is similarly important for understanding and interpreting what UFOs meant to 20th century America.

Skepticism of UFOs and Alien Encounters

Scientists and astronomers express varying degrees of enthusiasm for the possibility of intelligent life in the universe. However, scientists generally dismiss the idea that there are aliens visiting Earth. In Pale Blue Dot: A Vision of the Human Future in Space , Carl Sagan reviews the possibilities of alien visitors to Earth, and suggests that there is good reason to be skeptical of them. Much of Sagan's work focuses on debunking folk stories and beliefs and tries to encourage more rigorous and skeptical thought. He similarly discussed criticism of beliefs in alien visitors in his earlier book, Demon Haunted World: Science as a Candle in the Dark .

This zealous criticism of belief in UFOs from Sagan, who was well known for his speculative ideas about the likelihood of alien civilizations, might seem to be a contradiction. Sagan himself had even speculated on the possibilities of visits by ancient aliens in his essay from the early 60s Direct Contact among Galactic Civilizations by Relativistic Interstellar Spaceflight .

How do we reconcile Sagan the skeptic with the imaginative Sagan? Far from a contradiction, these two parts of Sagan's perspective offer a framework for understanding him and the interchange between science and myth about life on other worlds. Skepticism and speculative imagination come together as two halves of the whole. It's essential to entertain and explore new ideas, however strange, while at the same time testing and evaluating the validity of those ideas.

NASA scientists propose new 'alien life evidence' scale

More nuance is needed in reporting possible evidence of E.T., a new paper argues.

As the search for extraterrestrial life heats up, scientists may need to step up their reporting game a bit.

Researchers should report evidence for alien life on a scale similar to the technological readiness level scale commonly used to assess the readiness of spaceflight components, a new paper argues. The goal is to make the search for life less "binary" — life or no life — and to express it more accurately in terms of agreed-upon scientific uncertainty.

The newly proposed alien-life evidence scale was outlined in a study published online Oct. 27 in the journal Nature that was led by NASA chief scientist Jim Green. The scale includes seven levels, which are subject to change depending on the type of environment involved and how the scientific community responds. 

For a Mars mission, for example, finding hints of a signature of life would register at Level 1 on the scale, and showing that the discovery was not due to contamination by Earth life would raise it to Level 2. The highest levels include verifying signs of life with several instruments (Level 6) and in different locations on a world (Level 7).

Related: 5 bold claims of alien life

"Until now, we have set the public up to think there are only two options: it's life or it’s not life," study co-author Mary Voytek, head of NASA's Astrobiology Program at NASA headquarters, said in a statement . "We need a better way to share the excitement of our discoveries and demonstrate how each discovery builds on the next, so that we can bring the public and other scientists along on the journey."

NASA expects that the new scale will have special resonance when it comes to Mars, as there have been several high-profile debates about potential signs of Red Planet life. In 1996, for example, a team of researchers suggested that they found compelling signs of Mars life in a Martian meteorite called Allan Hills 84001  (ALH84001). The report remains controversial 25 years later.

Get the Space.com Newsletter

Breaking space news, the latest updates on rocket launches, skywatching events and more!

Another debate was sparked in 2015, when data gathered by NASA's Mars Reconnaissance Orbiter suggested that the signature of hydrated salts was associated with intriguing, seasonally occurring dark streaks on the Red Planet known as recurring slope lineae (RSL). Some scientists think these salts resulted from evaporation of briny water, but others say RSL are more likely caused by dry landslides.

— The search for alien life explained — 10 exoplanets that could host alien life — 6 most likely places for alien life in the solar system

While NASA did not allude to past research in describing the new scale in the press release, the agency did point out that astrobiology — as well as all of science — is a process that includes "asking questions, coming up with hypotheses, developing new methods to look for clues and ruling out all alternative explanations." 

"Any individual detection may not be completely explained by a biological process and must be confirmed through follow-up measurements and independent investigations," agency officials explained in the statement. "Sometimes, there are problems with the instruments themselves. Other times, experiments don’t turn up anything at all but still deliver valuable information about what doesn’t work or where not to look. "

NASA officials emphasized that the scale is meant to spur discussion in the community. The scale is also subject to change as large agency missions get underway later in the 2020s, including a planned Mars sample return mission and the Europa Clipper launch to a potentially habitable moon of Jupiter.

Follow Elizabeth Howell on Twitter @howellspace . Follow us on Twitter @Spacedotcom or Facebook .  

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

Elizabeth Howell (she/her), Ph.D., is a staff writer in the spaceflight channel since 2022 covering diversity, education and gaming as well. She was contributing writer for Space.com for 10 years before joining full-time. Elizabeth's reporting includes multiple exclusives with the White House and Office of the Vice-President of the United States, an exclusive conversation with aspiring space tourist (and NSYNC bassist) Lance Bass, speaking several times with the International Space Station, witnessing five human spaceflight launches on two continents, flying parabolic, working inside a spacesuit, and participating in a simulated Mars mission. Her latest book, " Why Am I Taller ?", is co-written with astronaut Dave Williams. Elizabeth holds a Ph.D. and M.Sc. in Space Studies from the University of North Dakota, a Bachelor of Journalism from Canada's Carleton University and a Bachelor of History from Canada's Athabasca University. Elizabeth is also a post-secondary instructor in communications and science at several institutions since 2015; her experience includes developing and teaching an astronomy course at Canada's Algonquin College (with Indigenous content as well) to more than 1,000 students since 2020. Elizabeth first got interested in space after watching the movie Apollo 13 in 1996, and still wants to be an astronaut someday. Mastodon: https://qoto.org/@howellspace

NASA greenlights 2028 launch for epic Dragonfly mission to Saturn's huge moon Titan

How exotic alien life could thrive in the giant molecular clouds of deep space

Quantum data beamed alongside 'classical data' in the same fiber-optic connection for the 1st time

Most Popular

• 2 SpaceX's private Polaris Dawn mission will set altitude record for female astronauts
• 3 This Week In Space podcast: Episode 125 — Back to Space School 2024
• 4 What happens when your warp drive fails? Scientists have the answer
• 5 Supermassive black holes have masses of more than a million suns – but their growth has slowed as the universe aged

• CUFOS Board, Consultants, and Friends
• Affiliated Organizations
• Get Involved
• International UFO Reporter
• Selected Articles
• Journal of UFO Studies
• Newsletters
• UFO Timeline 
• Other Books
• Other UFO Periodicals
• External Resources
• NICAP Publications
• NICAP Documents
• Recommended Books
• Classic UFO Cases 
• UFO Catalogues
• Project Blue Book
• Government Documents
• Frequently Asked Questions
• So You Want to be a Ufologist?
• Research Projects
• Classification Systems
• Nocturnal Lights
• Daylight Discs
• Triangular UFOs
• Radar and Radar-Visual
• Close Encounters of the First Kind
• Close Encounters of the Second Kind
• Close Encounters of the Third Kind
• Pre-1940 Cases
• Foo Fighters
• Ghost Rockets
• Ghost Lights
• Ball Lightning
• Related Phenomena
• Hynek Articles and Talks
• Hynek Archives
• Hynek Videos
• Report a Sighting

Select Page

The 2024 AARO Report

2023, the Year in Review

What is the Truth?

History was made one summer day two years after the end of World War II. Nine silvery objects gleaming in the afternoon sun astonished a private pilot, Kenneth Arnold, as they flew at extraordinary speed past Mount Rainier, Washington, “like saucers skipping over water.” Newspapers dubbed these objects “flying saucers” and tallied several thousand sightings over the next two weeks in June–July 1947.

More Stories

• The Magazine
• Stay Curious
• The Sciences
• Environment
• Planet Earth

The Infrared Images for Dyson Spheres Could be Evidence of Star-Harnessing Alien Technology

What are alien megastructures and could they be signs of alien civilizations the search for extraterrestrial civilizations is rife with debate..

In the modern age, the search for extraterrestrial life requires a unique mind. A researcher must have the openness and creativity to imagine something beyond our current knowledge of the universe. At the same time, the researcher, if they are to be taken seriously, must also be skilled enough to analyze high-powered astronomical imagery through supercomputing, artificial intelligence, or other means.

The researchers behind project Hephaistos, a Swedish-based effort to identify traces of alien life in the cosmos, fit this bill. They are extensively published astrophysicists with a shared dream: that the observable universe may contain signs of far-away civilizations yet unrecognized.

Earlier this year, the group published a paper documenting their use of machine learning to comb through large datasets of infrared images for Dyson spheres — networks of alien satellites harvesting energy from a star. The idea was old, but the scientists’ AI-forward approach was new.

“If you want to do this, you kind of have to try something that hasn’t been tried before,” says project Hephaistos leader Erik Zackrisson .

In their paper, project Hephaistos identified seven candidates for further research — star’s that appeared to be encircled by something like a Dyson sphere.

Just a couple of months after the publication, another research team called Project Hephaistos’ results into question . The truth is still being sorted out.

What Is a Dyson Sphere?

Many good hypotheses have come from science fiction, and this is especially true in the search for alien civilizations. Freeman Dyson credited the initial idea for Dyson spheres to Olaf Stapledon.

As it turns out, Stapledon’s sprawling 1937 science-fiction novel, Star Maker , includes just a brief mention of an alien civilization that could harvest the energy of stars. From this line, Dyson imagined that an advanced technological society would inevitably turn to its sun for a plentiful and consistent power supply.

According to Zackrisson, a common misconception about Dyson Spheres comes from their name. Likely, a Dyson Sphere would not actually be a sphere. Instead, it would be a web-like network of satellites in orbit around a star. The satellites would harvest energy from the star, much like solar panels harvest light energy from our sun.

Read More: What Does Extraterrestrial Mean and Why Are Experts Looking for It?

Challenges in Identifying Potential Dyson Spheres

When project Hephaistos went looking for Dyson Spheres, they programmed their model to spot stars that were partially obscured by objects that looked like they could be energy-harvesting satellites. Then, they eliminated every result that they could explain away through corrupted data or known “astrophysical phenomena.”

“The problem is that there are mundane astronomical objects that also give you infrared excess,” Zackrisson explains. “You want to get rid of those.”

Images from the project’s seven candidates look much like a shag rug with chocolate crumbs dusting its surface. What looks like shag is the intense heat produced by a given star’s nuclear fusion. And researchers are interested in those chocolate crumbs.

Like any solid object, they obscure the intense heat of the star from view. Yet, each crumb of interest also gives off a discernible amount of infrared radiation consistent with the “waste heat” that researchers would expect an energy-harvesting satellite to emit.

Read More: The Secret Origins of the Search for Extraterrestrial Intelligence

Could Space Dust Explain the Mysterious Infrared Images?

The British team that called Project Hephaistos’ results into question, led by astrophysicist Tongtian Ren, proposed an alternate theory. According to the researchers, Project Hephaistos’ chocolate crumbs were interference from hot, dust-obscured galaxies in the foreground. Basically, irradiated space dust – not alien civilization – was responsible for the phenomena.

Zackrisson concedes that three of the candidates seem to be hot, dust-obscured galaxies. But the mystery is not solved yet.

“The question is, what are those for which we don’t know yet. The jury is still out,” he says.

When Ren and his co-authors published their critique, the prospect of nearby alien civilizations once again seemed to lose some permanence in the collective imagination of alien enthusiasts. Yet, Project Hephaistos’ other four candidates are still awaiting confirmation or refutation. And, either way the evidence goes, one bunk result will do little to dissuade searchers — especially as new methods emerge.

“Radio SETI dates back to the 1960s,” Zackrisson says, referring to the acronym for the Search for Extraterrestrial Intelligence (SETI). “Back then, they didn’t have infrared telescopes. Astronomy has entered the era of big data, so we have these databases of billions of objects in the sky.”

Read More: New SETI Tool Expands the Search for Intelligent Life in the Universe

Article Sources

Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:

Monthly Notices of the Royal Astronomical Society. Project Hephaistos – II. Dyson sphere candidates from Gaia DR3, 2MASS, and WISE

Project Hephaistos leader. Erik Zackrisson

American Astronomical Society. Background Contamination of the Project Hephaistos Dyson

World Cat. Star Maker

Gabe Allen is a Colorado-based freelance journalist focused on science and the environment. He is a 2023 reporting fellow with the Pulitzer Center and a current master's student at the University of Colorado Center for Environmental Journalism. His byline has appeared in Discover Magazine, Astronomy Magazine, Planet Forward, The Colorado Sun, Wyofile, and the Jackson Hole News&Guide.

• human spaceflight
• space exploration
• spaceflight

Already a subscriber?

Register or Log In

Keep reading for as low as $1.99!

Sign up for our weekly science updates.

Save up to 40% off the cover price when you subscribe to Discover magazine.

Articles on Aliens

Displaying 1 - 20 of 97 articles.

Why do astronomers look for signs of life on other planets based on what life is like on Earth?

Cole Mathis , Arizona State University

Dyson spheres: astronomers report potential candidates for alien megastructures – here’s what to make of it

Simon Goodwin , University of Sheffield

AI may be to blame for our failure to make contact with alien civilisations

Michael Garrett , University of Manchester

The planetary orbit in Netflix’s ‘3 Body Problem’ is random and chaotic, but could it exist?

Peter Watson , Carleton University

The beginnings of modern science shaped how philosophers saw alien life – and how we understand it today

Philip C. Almond , The University of Queensland

3 Body Problem: is the universe really a ‘dark forest’ full of hostile aliens in hiding?

Tony Milligan , King's College London

The Solar System used to have nine planets. Maybe it still does? Here’s your catch-up on space today

Sara Webb , Swinburne University of Technology and Rebecca Allen , Swinburne University of Technology

UFOs: how astronomers are searching the sky for alien probes near Earth

Beatriz Villarroel , Stockholm University

UFOs: how Nasa plans to get to the bottom of unexplained sightings

Christopher Pattison , University of Portsmouth

How to prove you’ve discovered alien life – new research

Peter Vickers , Durham University and Sean McMahon , The University of Edinburgh

Have we really found the first samples from beyond the Solar System? The evidence is not convincing

Monica Grady , The Open University

What is most likely going on in Area 51? A national security historian explains why you won’t find aliens there

Christopher Nichols , The Ohio State University

Whistleblower calls for government transparency as Congress digs for the truth about UFOs

Chris Impey , University of Arizona

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

David Delgado Shorter , University of California, Los Angeles ; Kim TallBear , University of Alberta , and William Lempert , Bowdoin College

Why people tend to believe UFOs are extraterrestrial

Barry Markovsky , University of South Carolina

How Alien mutated from a sci-fi horror film into a multimedia universe

Nathan Abrams , Bangor University and Gregory Frame , University of Nottingham

‘Habits of civilised life’: how one state forced Indigenous people to meet onerous conditions to obtain citizenship

Peter Prince , University of Sydney

What would aliens learn if they observed the Earth? Our study provides an answer

Jupiter’s moons hide giant subsurface oceans – two missions are sending spacecraft to see if these moons could support life

Mike Sori , Purdue University

Starseeds: psychologists on why some people think they’re aliens living on Earth

Ken Drinkwater , Manchester Metropolitan University ; Andrew Denovan , University of Huddersfield , and Neil Dagnall , Manchester Metropolitan University

Related Topics

• Curious Kids
• Extraterrestrial life

Top contributors

University Distinguished Professor of Astronomy, University of Arizona

Sir Bernard Lovell chair of Astrophysics and Director of Jodrell Bank Centre for Astrophysics, University of Manchester

Senior research fellow, Curtin University

Professor of Planetary and Space Sciences, The Open University

Professor of Astronomy and Astrophysics, Penn State

James Martin Research Fellow, Future of Humanity Institute & Oxford Martin School, University of Oxford

Professor of Geophysics, Royal Holloway University of London

Lecturer, Centre for Astrophysics and Supercomputing, Swinburne University of Technology

Professor in Applied Cognitive Psychology, Manchester Metropolitan University

PhD in Evolutionary Biology, University of Oxford

Professor of Extragalactic Astronomy, Head of the Astrophysics Group, University of Bath

Senior Lecturer and Researcher in Cognitive and Parapsychology, Manchester Metropolitan University

Professor of Astrophysics Education, The Open University

Professor (Astrophysics), University of Southern Queensland

Professor of Planetary Geosciences, The Open University

• X (Twitter)
• Unfollow topic Follow topic

Coin Prices

$0.00001495

$0.00000904

$0.02488482

$0.00015307

$0.00002078

$0.02184493

$0.00953343

$0.00000092

$0.00000039

$0.01573581

$0.01597747

$0.00003446

$0.00009062

$0.00000047

$0.00518447

$0.00971699

$0.00000114

$0.02630575

$0.03789016

$0.00355725

$0.00432291

$0.03509094

$0.00189701

$0.03236173

$0.04404059

$0.00623678

$0.00448116

$0.01215486

$0.01519989

$0.00476314

$0.02716373

$0.02488424

$0.00071082

$0.02363967

Aliens Could Be ‘Walking Among Us’, Harvard Researchers Say

A peer-reviewed study urges the scientific community to be open to the possibility of aliens on earth—or hiding on the moon..

Decrypt’s Art, Fashion, and Entertainment Hub.

A new research paper from a team at Harvard University and Montana Technological University suggests that aliens have likely visited Earth—and could still be living among us in secret.

The peer-reviewed report more specifically argues that the scientific community should be open to the possibilities presented by Unidentified Anomalous Phenomena (UAP). The researchers explored the “cryptoterrestrial hypothesis,” a subset of a theory that UAP sightings may be the activities of non-human intelligent beings.

“UAP may reflect activities of intelligent beings concealed in stealth here on Earth (e.g., underground), and/or its near environs (e.g., the moon), and/or even ‘walking among us’ (e.g., passing as humans),” the authors explain.

“Fundamentally, UAP constitute an extraordinary empirical mystery, which science is surely obligated to investigate, yet has rarely done so—at least in an open, public, visible way,” the report adds.

UAP can appear in different forms, including strange lights in the sky or objects moving over or under the surface of Earth’s oceans. Most commonly, these events are labeled as Unidentified Aerial Phenomena (UAP)—or Unidentified Flying Objects (UFOs)—that witnesses describe as drones or even alien spaceships.

The report did not directly assert or deny the existence of extraterrestrial life but asked the scientific community to be open to the idea—including the possibility that aliens could be living in underground bases on Earth and the moon.

“Although this idea is likely to be regarded skeptically by most scientists, such are the nature of some UAP,” the researchers declared. “We argue this possibility should not be summarily dismissed, and instead deserves genuine consideration in a spirit of epistemic humility and openness.”

Their work was published in the open-access journal Philosophy and Cosmology , an international, double-blind peer-reviewed outlet of the International Society of Philosophy and Cosmology. The report was authored by Tim Lomas, Brendan Case, and Michael Masters, who did not respond to a request for comment from  Decrypt .

A “ double-blind ” or “double anonymized” peer review is a process used by academic journals to ensure that articles are fairly reviewed by experts in the field while concealing the identity of both the authors and the reviewers, with only the editor knowing who they are.

The paper broke down four categories of the cryptoterrestrial hypothesis: Human cryptoterrestrials would be an advanced ancient human civilization, like the mythical Atlantis, destroyed in an apocalypse. Hominids and theropod cryptoterrestrials would be animals that evolved in stealth, as portrayed in movies and TV shows like Land of the Lost or more recently in Legendary Pictures’ Monterverse . Former extraterrestrials, or extratemporal cryptoterrestrials, include aliens or future descendants who arrived on Earth via time travel, such as those depicted in the BBC television series Primeval . The final category is magical cryptoterrestrials, entities resembling earthbound or fallen angels that interact with humans in seemingly magical ways.

The possibility of extraterrestrial life on or around Earth ramped up in 2023 as the U.S. government released classified documents related to UAP sightings. Last year, during a congressional hearing before the House Oversight Subcommittee on National Security, witnesses who claim to have seen UAPs firsthand said they pose a serious national security threat.

"If UAPs are foreign drones, it's an urgent national security problem; if it's something else, it's an issue for science," executive director of Americans for Safe Aerospace Ryan Graves told the committee. "In either case, unidentified objects are a concern for flight safety, and the American people deserve to know what is happening in our skies."

For decades, the U.S. government has been accused of hiding the existence of alien life, to which Tennessee Rep. Tim Burchett said Congress has had enough.

“We’re done with the cover-ups,” he said.

In January, Congressman Robert Garcia (D-CA) and Congressman Glenn Grothman (R-WI) introduced the ‘Safe Airspace for Americans Act’ to make it easier for civilian pilots and personnel to report UAPs. On Tuesday, Garcia announced his proposed amendments to the National Defense Authorization Act were blocked in the House.

My 3 UAP amendments to the National Defense Authorization Act have been blocked from being considered by House Republican leadership. We must continue to fight for transparency and take seriously national security concerns and the public interest. We will continue pushing. — Congressman Robert Garcia (@RepRobertGarcia) June 12, 2024

Despite witness testimony, the U.S. Department of Defense’s All-domain Anomaly Resolution Office (AARO) released a separate report in March regarding UAPs, concluding there was no evidence of visitors from the stars.

"AARO has found no verifiable evidence that any UAP sighting has represented extraterrestrial activity," AARO acting Director Tim Phillips said during a briefing at the Pentagon. "AARO has found no verifiable evidence that the U.S. government or private industry has ever had access to extraterrestrial technology. AARO has found no indications that any information was illegally or inappropriately withheld from Congress."

Edited by Ryan Ozawa .

Generally Intelligent Newsletter

To revisit this article, visit My Profile, then View saved stories .

• The Big Story
• Newsletters
• Steven Levy's Plaintext Column
• WIRED Classics from the Archive
• WIRED Insider
• WIRED Consulting

The Dumb Alien Mummy Story Takes an Entirely Predictable Turn

On September 12, ufologist and journalist Jaime Maussan presented what he claimed to be evidence of alien life to the Congress of Mexico. On September 19, Mexico’s scientific community gathered for a conference to ask a simple question in return: “Extraterrestrials or Llama Skeletons?”

The answer was right there in the subtitle of the conference itself: “Science responds to the charlatans and the gullible.” If Maussan had shocked Mexico and the world with his outlandish claims, this was Mexico’s scientific community fighting back. Toward the end of the conference, Alejandro Frank, a professor of mathematical physics at Universidad Nacional Autónoma de México (UNAM) and the host of the event, summed things up: “Faced with the serious problems we are experiencing in Mexico and the entire planet, starting with climate change, war, and pandemics, it is sad to gather to talk about the misdeeds of a professional charlatan.”

Frank said the scientists had not gathered to discuss Maussan’s “decades of ridiculous conspiracy claims,” but rather because of where Maussan had delivered his latest outlandish claims. Maussan’s appearance in Mexico’s Congress had, Frank argued, “turned the world upside down” and made scientific rationality in Mexico the subject of ridicule. “What is at stake here is whether our country will follow science or superstitions and quackery.”

While Maussan’s extraterrestrial claims are laughable, the damage they risk doing to science in Mexico, and worldwide, is a serious matter. Frank pointed to the polarization of Mexican politics, especially around urgent issues like the climate crisis, as an especially alarming example of how the country’s scientific reputation was already suffering. Following the alien debacle, Frank had called on Mexico’s Consejo Nacional de Ciencia y Tecnología, or National Council on Science and Technology, to speak up and take action. “The agency has been silent about the facts surrounding the Nazca mummies, which are increasingly becoming famous as the ‘Mexican mummies.’”

José Franco, a researcher at UNAM’s Astronomy Institute, started the conference with a presentation entitled “Life in the Universe,” where he spoke about DNA and RNA, interstellar chemistry, the radio spectra of Orion’s KL nebula, and cloverleaf quasars.

He spoke of exobiology, the area that studies the possibility of life outside Earth; the direct search for microbial life in celestial bodies; meteorites, the moon, Mars, Europa, Enceladus, and Venus. He also spoke about humanity’s indirect search for alien life—about the messages sent from the Arecibo telescope; the Pioneer plaques; the Voyager 1 and 2 Golden records; the message sent from Ukraine to Gliese 581c , a planet with some conditions similar to Earth’s, in 2008; and another transmission, also in 2008, of the Beatles song “Across the Universe,” directed toward the star Polaris .

“Hayabusa2 was sent to the Ryugu Asteroid, returned to Earth, and is already in the hands of scientists in Japan, and NASA,” Franco said. He mentioned the Osiris-Rex sample collection mission, which collected around 250 grams of rubble from an asteroid. He also touched on the nine probes sent to Mars, among them the celebrated Perseverance. “No life has been found anywhere, and neither has intelligence been found in Congress,” Franco joked.

Gabriela Frías, a philosophy of science researcher, described recent events in Mexico’s Congress as “a pseudoscientific event, which appeals to our fantasies, desires, and fears.” During his presentation, Maussan pointed to a “carbon-14 analysis” conducted on the Nazca mummies by scientists at UNAM. Maussan had claimed this, in part, as proof that he was presenting “nonhuman beings.” UNAM has since distanced itself from “any subsequent use, interpretation, or misrepresentation of the results.”

In a statement, UNAM said it was essential that the search for alien life be approached “with the support of scientific research institutions, and following the rigorous ethical standards inherent to research.” Maussan’s appearance in Congress was the opposite of that.

This article was originally published by WIRED en Español .

You Might Also Like …

Politics Lab: Get the newsletter and listen to the podcast

What happens when you give people free money

Not everyone loses weight on Ozempic

The Pentagon wants to spend $141 billion on a doomsday machine

Event: Join us for the Energy Tech Summit on October 10 in Berlin

February 1, 2023

19 min read

The Search for Extraterrestrial Life as We Don’t Know It

Scientists are abandoning conventional thinking to search for extraterrestrial creatures that bear little resemblance to Earthlings

By Sarah Scoles

Life on other planets might not look like any beings we're used to on Earth. It may even be unrecognizable at first to scientists searching for it.

William Hand

S arah Stewart Johnson was a college sophomore when she first stood atop Hawaii’s Mauna Kea volcano. Its dried lava surface was so different from the eroded, tree-draped mountains of her home state of Kentucky. Johnson wandered away from the other young researchers she was with and toward a distant ridge of the 13,800-foot summit. Looking down, she turned over a rock with the toe of her boot. To her surprise, a tiny fern lived underneath it, having sprouted from ash and cinder cones. “It felt like it stood for all of us, huddled under that rock, existing against the odds,” Johnson says.

Her true epiphany, though, wasn’t about the hardiness of life on Earth or the hardships of being human: It was about aliens. Even if a landscape seemed strange and harsh from a human perspective, other kinds of life might find it quite comfortable. The thought opened up the cosmic real estate, and the variety of life, she imagined might be beyond Earth’s atmosphere. “It was on that trip that the idea of looking for life in the universe began to make sense to me,” Johnson says.

Later, Johnson became a professional at looking. As an astronomy postdoc at Harvard University in the late 2000s and early 2010s she investigated how astronomers might use genetic sequencing—detecting and identifying DNA and RNA—to find evidence of aliens. Johnson found the work exciting (the future alien genome project!), but it also made her wonder: What if extraterrestrial life didn’t have DNA or RNA or other nucleic acids? What if their cells got instructions in some other biochemical way?

On supporting science journalism

If you're enjoying this article, consider supporting our award-winning journalism by subscribing . By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.

As an outlet for heretical thoughts like this, Johnson started writing in a style too lyrical and philosophical for scientific journals. Her typed musings would later turn into the 2020 popular science book The Sirens of Mars . Inside its pages, she probed the idea that other planets were truly other, and so their inhabitants might be very different, at a fundamental and chemical level, from anything on this world. “Even places that seem familiar—like Mars, a place that we think we know intimately—can completely throw us for a loop,” she says. “What if that’s the case for life?”

If Johnson’s musings are correct, the current focus of the hunt for aliens—searching for life as we know it—might not work for finding biology in the beyond. “There’s this old maxim that if you lose your keys at night, the first place you look is under the lamppost,” says Johnson, who is now an associate professor at Georgetown University. If you want to find life, look first at the only way you know life can exist: in places kind of like Earth, with chemistry kind of like Earthlings’.

Much of astrobiology research involves searching for chemical “biosignatures”—molecules or combinations of molecules that could indicate the presence of life. But because scientists can’t reliably say that ET life should look, chemically, like Earth life, seeking those signatures could mean we miss beings that might be staring us in the face. “How do we move beyond that?” Johnson asks. “How do we contend with the truly alien?” Scientific methods, she thought, should be more open to varieties of life based on varied biochemistry: life as we don’t know it. Or, in a new term coined here, “LAWDKI.”

Now Johnson is getting a chance to figure out how, exactly, to contend with that unknown kind of life, as the principal investigator of a new NASA-funded initiative called the Laboratory for Agnostic Biosignatures (LAB). LAB’s research doesn’t count on ET having specific biochemistry at all, so it doesn’t look for specific biosignatures. LAB aims to find more fundamental markers of biology, such as evidence of complexity—intricately arranged molecules that are unlikely to assemble themselves without some kind of biological forcing—and disequilibrium, such as unexpected concentrations of molecules on other planets or moons. These are proxies for life as no one knows it.

Maybe someday, if LAB has its way, they will become more than proxies. These signals could help answer one of humankind’s oldest questions—Are we alone?—and show us that we’re not so special, and neither is our makeup.

Life, Astro Life or Lyfe

Part of the difficulty in searching for life of any sort is that scientists don’t agree on how life started in the first place—or what life even is . One good attempt at a definition came in 2011 from geneticist Edward Trifonov, who collated more than 100 interpretations of the word “life” and distilled them into one overarching idea: it’s “self-reproduction with variations.” NASA formulated a similar working definition years earlier, in the mid-1990s, and still uses it to design astrobiology studies. Life, according to this formulation, “is a self-sustaining chemical system capable of Darwinian evolution.”

Credit: Jen Christiansen

Neither of those classical definitions requires a particular chemistry. On Earth, of course, life runs on DNA: deoxyribonucleic acid. DNA is made up of two twisted strands, each comprising alternating sugar and phosphate groups. Stuck to every sugar is a base—the As (adenine), Gs (guanine), Cs (cytosine), and Ts (thymine). Together the bases and sugar-phosphates form nucleotides; DNA itself is a nucleic acid. RNA is kind of like single-stranded DNA—among other things, it helps translate DNA’s instructions into actual protein production.

The simple letters in a genetic sequence, strung together in a laddered order, carry all the information needed to make you, squirrels and sea anemones. DNA can replicate, and DNA from different organisms (when they really, really love one another) can mix and meld to form a new organism that can replicate itself in turn. If biology elsewhere relied on this same chemistry, it would be life as we know it.

Scientists assume all forms of life would need some way to pass down biological instructions whose shifts could also help the species evolve over time. But it’s conceivable that aliens might not make these instructions out of the same chemicals as ours—or in the same shape. For instance, starting in the 1990s, Northwestern University researchers made SNAs, spherical nucleic acids.

Alien life could have genetic code with, say, different bases. NASA-supported 2019 research, from the Foundation for Applied Molecular Evolution, successfully created synthetic DNA that used the four old-school bases and four new ones: P, Z, B and S. Scientists have also altered the strand part of genetic code, creating XNA—where X means anything goes—that uses a molecule such as cyclohexene (CeNA) or glycol (GNA), rather than deoxyribose. Big thinkers have long suggested that rather than using carbon as a base, as all these molecules do, perhaps alien life might use the functionally similar element silicon—meaning it wouldn’t have nucleic acids at all but other molecules that perhaps play the same role. If we can whip up such diversity in our minds and our labs, shouldn’t the universe be even more creative and capable?

It’s for that reason that LAB collaborator Leroy Cronin of the University of Glasgow doesn’t think scientists should even be talking about biology off-Earth at all. “Biology is unique,” he proclaims. RNA, DNA, proteins, typical amino acids? “Only going to be found on Earth.” He thinks someday people will instead say, “We’re looking for “astro life.” (LAWDKI has yet to catch on.)

Stuart Bartlett, a researcher at the California Institute of Technology and unaffiliated with LAB, agrees with the linguistic critique. The search for weird life isn’t actually a search for life, Bartlett argues. It’s a search for “lyfe,” a term proposed in a 2020 article he co-authored in, ironically, the journal Life . “Lyfe,” the paper says, “is defined as any system that fulfills all four processes of the living state.” That means that it dissipates energy (by, say, eating and digesting), uses self-sustaining chemical reactions to make exponentially more of itself, maintains its internal conditions as external conditions change, and takes in information about the environment that it then uses to survive. “Life,” meanwhile, the paper continues, “is defined as the instance of lyfe that we are familiar with on Earth.”

Bartlett’s work, though separate from LAB’s, emerges from the same fascination: “That mysterious, opaque transition between things like physics and chemistry that we understand fairly well,” he says, “and then biology that is still shrouded in mystery.” How life becomes life at all is perhaps the most central question of astrobiology.

Trying to figure out how biology emerged on the planet we know best is the province of “origin of life” studies. There are two main hypotheses for how clumps of chemistry became lumps of biology—a process called abiogenesis. One holds that RNA arose able to make more of itself, because that’s what it does, and that it could also catalyze other chemical reactions. Over time that replication led to beings whose makeup relied on that genetic code. The “metabolism-first” framework, on the other hand, posits that chemical reactions organized in a self-sustaining way. Those compound communities and their chemical reactions grew more complex and eventually spit out genetic code.

Those two main hypotheses aren’t mutually exclusive. John Sutherland, a chemist at the Medical Research Council Laboratory of Molecular Biology, is co-director of a group called the Simons Collaboration on the Origins of Life, which merges previous ideas about how one or another subsystem, such as genetics or early metabolism, came first. But if he’s being real, Sutherland admits he doesn’t understand how biology got started. No one does.

And until scientists know more about how things probably went down on the early Earth, Sutherland argues, there’s no way to estimate how common extraterrestrial anything might be. It doesn’t matter that there are trillions of stars in billions of galaxies: If the events that led to life are supremely uncommon, those many solar systems might still not be enough, statistically, to have resulted in abiogenesis—in other beings.

Bio-Agnostic

The first issue of the academic journal Astrobiology , more than two decades ago, featured an article by Kenneth Nealson and Pamela Conrad called “A Non-Earth-centric Approach to Life Detection.” But taking a non-Earth-centric approach isn’t easy for our brains, which formed in this environment. We are notoriously bad at picturing the unfamiliar. “It’s one of the biggest challenges we have, like imagining a color we’ve never seen,” Johnson says.

So astrobiologists often end up looking for aliens that resemble Earth life. Astronomers like to consider oxygen in an exoplanet atmosphere as a potential indicator of life—because we breathe it—although a planet can fill up with that gas in less lively ways. On Mars, researchers have been psyched by puffs of methane, organic molecules, and the release of gas after soil was fed a solution of what we on Earth call nutrients, perhaps indicating metabolism. They create terms like “the Goldilocks zone” for the regions around stars where planets could host liquid water, implying that what’s just right for Earth life is also just right everywhere else.

Even when scientists do discover biology unfamiliar to them, they tend to relate it to something familiar. For instance, when Antonie van Leeuwenhoek saw single-celled organisms through his microscope’s compound lens in the 17th century, he dubbed them “animalcules,” or little animals, which they are not.

Heather Graham, who works at NASA’s Goddard Space Flight Center and is LAB’s deputy principal investigator, sees van Leeuwenhoek’s discovery as a successful search for LAWDKI, close to home. The same description applies to scientists’ discovery of Archaea, a domain of ancient single-celled organisms first recognized in the 1970s. “If you reframe those discoveries as agnostic biosignatures in action, you realize that people have been doing this for a while,” Graham says.

Around 2016, Johnson joined their ranks, finding some like-minded nonbelievers who wanted to probe that darkness. At an invitation-only NASA workshop about biosignatures, Johnson sat at a table with scientists like Graham, gaming out how they might use complexity as a proxy for biology. On an exaggerated macroscale, the idea is that if you come across a fleet of 747s on Mars, you might not know where they came from, but you know they’re unlikely to be random. Someone, or something, created them.

After the meeting, Johnson and her co-conspirators put in a last-minute proposal to develop an instrument for NASA. It would find and measure molecules whose shapes fit physically together like lock and key because that rarely happens in random collections of chemical compounds but pops up all over living cells. The instrument idea, though, didn’t make the cut. “That’s when we realized, ‘Okay, we need to roll this back and do a lot more fundamental work,’” Graham says.

The space agency would give them a chance to do so, soon putting out a call for “Interdisciplinary Consortia for Astrobiology Research.” It promised multiple years of funding to dig deeper into Johnson and her associates’ lunch-table ideas. They needed a larger team, though, so they pinged planetary scientists, biologists, chemists, computer scientists, mathematicians and engineers—some space-centric to the core and others, Johnson says, “just beginning to consider the astrobiology implications of their work.” It was particularly important to do this now because researchers are planning to send life-detection instruments to destinations such as the solar system moons Europa, Enceladus and Titan, more exotic than most of the worlds visited so far. “Most of these other places we’re beginning to think about as targets for astrobiology are really weird and different,” Johnson says. If you’re going to a weird and different place, you might expect weird and different life, squirming invisibly beyond the reach of a lamppost’s light.

Their pitch worked: The expanded lunch table became LAB. Now the project, a spread-out coalition of scientists more than a single physical laboratory, is a few years deep into its work. The researchers aim to learn how things like the complexity of a surface, anomalous concentrations of elements and energy transfer—such as the movement of electrons between atoms—might reveal life as no one knows it.

LAB’s research is a combination of fieldwork, lab projects and computation. One project is a planned visit to Canada’s Kidd Creek Mine, which drops nearly 10,000 feet into the ground. Its open pit looks like a quarry reaching toward the seventh circle of hell. At those depths, around 2.7 billion years ago, an ocean floor brewed with volcanic activity, which left sulfide ore behind. The conditions are similar(ish) to what astronomers believe they might find on an “ocean world” like Europa. In the mine, the scientists hope to probe the differences between minerals that formed by crystallization—when atoms fall out of solution and into an ordered, lattice structure in the same place they are now—and evidence of biology.

The two kinds of materials can look superficially alike because they’re both highly ordered. But the team aims to show that geochemical models, which simulate how water saturated with chemicals will precipitate them out, will predict the kind of abiotic crystals found there. Kidd Creek, for instance, has its own sort: Kiddcreekite, a combination of the copper, tin, tungsten and sulfur that crystallizes from the water. Those same models, however, aren’t likely to predict biological structures, which form according to different forces and rules. If that turns out to be true, the models may prove useful when applied to alien geochemical conditions to predict the naturally forming minerals. Anything else that’s found there, the thinking goes, might be alive.

Johnson is reaching back to her postdoc days, using the genetic sequencers whose relevance she called into question back then. The group, though, has found a way to make them more agnostic. The researchers plan to use the instruments to investigate the number of spots on a cell’s surface where molecules can attach themselves—like the places where antibodies stick to cells. “We had this hypothesis that there are more binding sites on something complicated like a cell than a small particle,” Johnson says, such as an unalive mote of dust. Something alive, in other words, should have more lock-and-key places.

To test this idea, they create a random pool of DNA snippets and send it toward a cell. Some snippets will hook up with the cell’s exterior. The scientists next remove and collect the bound snippets, then capture the unbound snippets and send them back to the target cell again, repeating the process for several cycles. Then they see what’s left at the end—how much has hooked on and how much is still free. In this way, the researchers can compare the keys locked into the cell with those attached to something like a dust particle.

The scientists will also scrutinize another key difference they suspect divides life and not-life: Things that are not alive tend to be at a kind of equilibrium with their environment. In contrast, something that’s alive will harness energy to maintain a difference from its surroundings, LAB member Peter Girguis of Harvard hypothesizes. “It’s using power to keep ourselves literally separate from the environment, defining our boundary,” he says. Take this example: When a branch is part of a tree, it’s alive, and it’s different—in a bordered way—from its environment. If you remove that life from its energy source—pluck the branch—it dies and stops using power. “In a matter of time, it disintegrates and becomes indistinguishable from the environment,” Girguis says. “In other words, it literally goes to equilibrium.”

The disequilibrium of living should show up as a chemical difference between an organism and its surroundings—regardless of what the surroundings, or the life, are made of. “I can go scan something, make a map and say, ‘Show me the distribution of potassium,’” Girguis says. If blobs of concentrated K appear, dotting the cartography only in certain spots, you may have biology on your hands.

Girguis’s LAB work intertwines with another pillar of the group’s research: a concept called chemical fractionation, which is how life preferentially uses some elements and isotopes and ignores others. A subgroup investigating this idea, led by Christopher House of Pennsylvania State University, can use the usual data that space instruments take to suss out the makeup of a planet or moon. “If you understand the fundamental rules about the inclusion or exclusion of elements and isotopes, then you can imagine a different ecosystem where it still behaves by similar rules, but the elements and isotopes are totally different,” House says. It could give disequilibrium researchers a starting point for which kinds of patterns to focus on when making their dotted maps.

Within House’s group, postdoc researchers are studying sediments left by ancient organisms in Western Australia. Looking at these rock samples, they try to capture patterns showing which elements or isotopes early Earth life was picky about. “We’re hopeful that we can start to generalize,” House says.

LAB’s computing team, co-led by Chris Kempes of the Santa Fe Institute, is all about such generalizing. Kempes’s research focuses on a concept called scaling—in this case, how the chemistry inside a cell changes predictably with its size and how the abundance of different-sized cells follows a particular pattern. With LAB, Kempes, House, Graham and their collaborators published a paper in 2021 in the Bulletin of Mathematical Biology about how scaling laws would apply to bacteria. For instance, if you sort a sample of biological material by size, differences pop out. Small cells’ chemistry looks a lot like their environment’s. “The bigger cells will be more and more different from the environment,” Kempes says.

The abundance of cells of different sizes tends to follow a relationship known as a power law: Lots of small things with a steep drop-off as cells get larger. If you took an extraterrestrial sample, then, and saw those mathematical relationships play out—small things that looked like their surroundings, with progressively larger things looking less like their environments, with lots of the former and few of the latter—that might indicate a biological system. And you wouldn’t need to know ahead of time what either “environment” or “biology” looked like chemically.

Cronin, a sort of heretic within this heretic group, has his own idea for differentiating between living and not. He’s an originator of something called assembly theory, a “way of identifying if something is complex without knowing anything about its origin,” he says. The more complex a molecule is, the more likely it is to have come from a living process.

That can sound like a bias in the agnosticism, but everyone generally concedes that life results from, as Sutherland puts it, “the complexification of matter.” In the beginning, there was the big bang. Hydrogen, the simplest element, formed. Then came helium. Much later there were organic molecules—conglomerations of carbon atoms with other elements attached. Those organic molecules eventually came together to form a self-sustaining, self-replicating system. Eventually that system started to build the biological equivalent of 747s (and then actual 747s).

In assembly theory, the complexity of molecules can be quantified by their “molecular assembly number.” It’s just an integer indicating how many building blocks are required to bond together, and in what quantities, to make a molecule. The group uses the word “abracadabra” (magic!) as an example. To make that magic, you first need to add an a and a b . To that ab , you can add r . To abr , toss in another a to make abra . Then attach a c , then an a and then a d , and you get abracad . And to abracad , you can add the abra that you’ve already made. That’s seven steps to make abracadabra , whose molecular assembly number is thus seven. The group postulated that a higher number meant a molecule would have a more complicated “fingerprint” on a mass spectrometer—a tool that separates a sample’s components by their mass and charge to identify what it’s made of. A complex molecule would show more distinct peaks of energy, in part because it was made of many bonds. And those peaks are a rough proxy for its assembly number.

Cronin had bragged that by doing mass spectrometry, he could measure the complexity of a molecule without even knowing what the molecule was. If the technique indicated that a molecule’s complexity crossed a given threshold, it probably came from a biological process.

Still, he needed to prove it. Through LAB, NASA gave him double-blind samples of material to yea or nay as biological. The material hailed from outer space, fossil beds and the sediments of bays, among other places. One of the samples was from the Murchison meteorite, a 220-pound hunk of rock, full of organic compounds. “They thought the technique would fail because Murchison is probably one of the most complex interstellar materials,” he says. But it succeeded: “It basically says Murchison seems a bit weird, but it’s dead.”

Another sample contained 14-million-year-old fossils, sculpted by biology but meant to fool the method into a “dead” hit because of their age. “The technique found that they were of living origin pretty easily,” Cronin says. His results appeared in Nature Communications in 2021 and helped to convince Cronin’s colleagues that his line of research was worthy. “There are a lot of skeptical people in [LAB’s] team, actually,” he says.

Aliens Discovered??

There is plenty of skepticism outside LAB as well. Some scientists question the need to search for unfamiliar life when we still haven’t done much searching for extraterrestrial life as we know it. “I think there’s still a lot we can explore before we go to life as we don’t know it,” says Martina Preiner of the Royal Netherlands Institute for Sea Research and Utrecht University.

Still, even among old-school astrobiology researchers looking for Earth-like signatures on exoplanets, the LAB approach has support. Victoria Meadows of the University of Washington has been thinking about such far-off signals for two decades. She’s seen the field change over that time—complexify, if you will. Scientists have gone from thinking “if you see oxygen on a planet, slam dunk,” to thinking “there are no slam dunks.” “I think what my team has helped provide and how the field has evolved is this understanding that biosignatures must be interpreted in the context of their environment,” she says. You have to understand a planet’s conditions, and those of its star, well enough to figure out what oxygen might mean . “It may be that the environment itself can either back up your idea that oxygen is due to life or potentially that the environment itself may produce a false positive,” she says, such as from an ocean boiling off.

In a lot of ways, Meadows says, looking for agnostic biosignatures is the ultimate way to take such cosmic conditions into account. “You have to understand the environment exquisitely to be able to tell that something anomalous—something that isn’t a planetary process—is operating in that environment,” she says. Still, this variety of alien hunting is in its infancy. “I think they’re really just starting off,” she says. “I think what LAB is doing in particular is a pioneering effort on really getting some science under this concept.”

Even so, Meadows isn’t sure how likely LAWDKI is. “The question is, ‘Is the environment on a [terrestrial] extrasolar planet going to be so different that the solutions are so different?’’ Meadows asks. If the conditions are similar and the chemicals are similar, it’s reasonable to think life itself will be similar. “We are expecting to see some similar science if these environments are similar, but of course I will expect that there’ll be things that will surprise us as well.” It’s for all these reasons that Meadows, whose work focuses on exoplanets, is working with the LAB scientists, whose research for now homes in on the solar system, to bring their two worlds together.

By the end of LAB’s grant, the team plans to develop instruments that will help spacecraft notice weird and different life close to home. “We’re extremely focused on the ultimate goal—how we can take these tools and techniques and help develop them to the point they can become instruments on space missions,” Johnson says.

No one piece of information, gathered from a single instrument, can reliably label something life, though. So the group is working toward suites of devices, drawing on all their focus areas, that work together in different environments, such as worlds wrapped in liquid versus rocky deserts. Graham is gathering sample sets that LAB’s subgroups can test in a round-robin way to see how the superimposition of their results stacks up. They might look for, say, molecules with big assembly numbers concentrated in bounded areas that look different from their environment.

Even if these approaches collectively find something, it’s unlikely to provide a definitive answer to the question “Are we alone?” It will probably yield a “maybe,” at least for a while. That grayness may disappoint those who’d like “Aliens discovered!” headlines, instead of “Aliens discovered?? Check back in 10 years.”

“I understand that frustration,” Johnson says, “because I’m a restless sort of person.” That restlessness relates in part to her own mortality. The end of the time when she’s out of equilibrium with her environment. The demise of her complexity, of her detectability and ability to detect. “We have these ephemeral lives,” she says. “We have this world that’s going to end. We have this star that’s going to die. We have this incredible moment. Here we are: alive and sentient beings on this planet.” All because, at some point, life started .

That may have happened tens or hundreds or thousands or millions or billions of other times on other planets. Or, maybe, it has only happened here. “It just feels,” Johnson says, “like an extraordinary thing that I want to know about the universe before I die.”

Sarah Scoles is a Colorado-based science journalist, a contributing editor at Scientific American and Popular Science and a senior contributor at Undark. Her newest book is Countdown: The Blinding Future of Nuclear Weapons (Bold Type Books, 2024).