Astrobiology Archives

May 24, 2016 by Paul Patton

Alien Minds I: Are Extraterrestrial Civilizations Likely to Evolve?

The face of a jumping spider — The face of a dimorphic jumping spider (Maevia inclemens). Spiders have a very different evolutionary history from more familiar animals with backbones, and function in a different regime of body sizes. Their sensory endowment is thus evocative of what we might find in aliens. Spiders typically have a total of eight eyes, In this image, four eyes are clearly visible as shiny black globes, and two additional eyes are partially visible around the side of the head. The large frontal eyes provide the acute vision needed to recognize and capture prey. The other eyes provide the spider with a broad field of view, extending even behind the head which allows it to detect a potential meal, and to avoid predators. This image was taken in 2005 by an author named ‘Opoterser’ for open use.

Is it likely that human level intelligence and technological civilization has evolved on other worlds? If so, what kinds of sensory and cognitive systems might extraterrestrials have? This was the subject of the workshop ‘The Intelligence of SETI: Cognition and Communication in Extraterrestrial Intelligence’ held in Puerto Rico on May 18, 2016. The conference was sponsored by the newly founded METI International (Messaging to ExtraTerrestrial Intelligence). One of the organization’s central goals is to build an interdisciplinary community of scholars concerned with designing interstellar messages that can be understood by non-human minds.

At present, the only clues we have to the nature of extraterrestrial minds and perception are those that can be garnered by a careful study of the evolution of mind and perception here on Earth. The workshop included nine speakers from universities in the United States and Sweden, specializing in biology, psychology, cognitive science, and linguistics. It had sessions on the evolution of cognition and the likely communicative and cognitive abilities of extraterrestrials.

Doug Vakoch, a psychologist and the founder and president of METI International, notes that astronomers and physicists properly concern themselves largely with the technologies needed to detect alien intelligence. However, finding and successfully communicating with aliens may require attention to the evolution and possible nature of alien intelligence. “The exciting thing about this workshop”, Vakoch writes, “is that the speakers are giving concrete guidelines about how to apply insights from basic research in biology and linguistics to constructing interstellar messages”. In this, the first installment dealing with the conference, we’ll focus on the question of whether the evolution of technological societies on other planets is likely to be common, or rare.

Dr. Douglas Vakoch is a Professor of clinical psychology and the founder and president of METI International. Photo by Mara Lavitt, used with permission.

We now know that most stars have planets, and rocky planets similar to or somewhat larger than the Earth or Venus are commonplace. Within this abundant class of worlds, there are likely to be tens of billions with conditions suitable for sustaining liquid water on their surfaces in our galaxy. We don’t yet know how likely it is that life will arise on such worlds. But suppose, as many scientists suspect, that simple life is abundant. How likely is it that alien civilizations will appear; civilizations with which we could communicate and exchange ideas, and which could make their presence known to us by signaling into space? This was a central question explored at the conference.

In addressing such questions, scientists have two main sets of clues to draw on. The first comes from the study of the enormous diversity of behavior and nervous and sensory systems of the animal species that inhabit our Earth; an endeavor that has been called cognitive ecology. The second set of clues come from modern biology’s central principle; the theory of evolution. Evolutionary theory can provide scientific explanations of how and why various senses and cognitive systems have come to exist here on Earth, and can guide our expectations about what might exist elsewhere.

Artist's impression of three newly-discovered exoplanets orbiting an ultracool dwarf star TRAPPIST-1. Credit: ESO/M. Kornmesser/N. Risinger (skysurvey.org). — Artist’s impression of three newly-discovered exoplanets orbiting an ultracool dwarf star TRAPPIST-1. Credit: ESO/M. Kornmesser/N. Risinger (skysurvey.org).

The basics of the electrochemical signalling that make animal nervous systems possible have deep evolutionary roots. Even plants and bacteria have electrochemical signalling systems that share some basic features with those in our brains. Conference presenter Dr. Anna Dornhaus studies how social insects make decisions collectively as an associate professor at the University of Arizona. She defines cognitive ability as the ability to solve problems with a nervous system, and sometimes also by social cooperation. An animal is more ‘intelligent’ if its problem solving abilities are more generalized. Defined this way, intelligence is widespread among animals. Skills traditionally thought to be the sole province of primates (monkeys and apes, including human beings) have now been shown to be surprisingly common.

Dr. Anna Dornhaus is an Associate Professor of Ecology and Evolutionary Biology at the University of Arizona, and a presenter at the Puerto Rico conference

For example, cognitive skills like social learning and teaching, generalizing from examples, using tools, recognizing individuals of one’s species, making plans, and understanding spatial relationships have all been shown to exist in arthropods (an animal group consisting of insects, spiders, and crustaceans). The evidence shows the surprising power of the diminutive brains of insects, and indicates that we know little of the relationship between brain size and cognitive ability.

But different animals often have different sets of cognitive skills, and if a species is good at one cognitive skill, that doesn’t necessarily mean it will be good at others. Human beings are special, not because we have some specific cognitive ability that other animals lack, but because we possess a wide range of cognitive abilities that are more exaggerated and highly developed than in other animals.

The cathedral termite mound — Termite mounds demonstrate that architecture and agriculture are not unique to humans. Housing one to two million inhabitants, they can reach 5 meters (17 feet) or more in height, and also extend beneath the surface of the ground. They are organized to ensure that appropriate levels of oxygen, moisture, and temperature are maintained. Although the inhabitants of a termite mound collectively weigh only 15 kilograms (33 lb), a typical mound will, in an average year, move a quarter of a metric ton (550 lb) of soil, and several tons of water. Using carefully prepared plant materials, termites “farm” a species of fungus that occupies eight times more space in the mound than they do. Photo taken by Brain Voon Yee Yap of cathedral termite mounds in the Northern Territories of Australia for open use.

Although the Earth, as a planet, has existed for 4.6 billion years, complex animals with hard body parts don’t appear in the fossil record until 600 million years ago, and complex life didn’t appear on land until about 400 million years ago. Looking across the animal kingdom as a whole, three groups of animals, following separate evolutionary paths, have evolved especially complex nervous systems and behaviors. We’ve already mentioned arthropods, and the sophisticated behaviors mediated by their diminutive yet powerful brains.

Molluscs, a group of animals that includes slugs and shellfish, have also produced a group of brainy animals; the cephalopods. The cephalopods include octopuses, squids, and cuttlefish. The octopus has the most complex nervous system of any animal without a backbone. As the product of a different evolutionary path, the octopus’s sophisticated brain has a plan of organization that is completely alien to that of more familiar animals with backbones.

The third group to have produced sophisticated brains are the vertebrates; animals with backbones. They include fishes, amphibians, reptiles, birds, and mammals, including human beings. Although all vertebrate brains bear a family resemblance, complex brains have evolved from simpler brains many separate times along different paths of vertebrate evolution, and each such brain has its own unique characteristics.

Along one path, birds have evolved a sophisticated forebrain, and with it, a flexible and creative capacity to make and use tools, an ability to classify and categorize objects, and even a rudimentary understanding of numbers. Following a different path, and based on a different plan of forebrain organization, mammals have also evolved sophisticated intelligence. Three groups of mammals; elephants, cetaceans (a group of aquatic mammals including dophins, porpoises, and whales), and primates (monkeys and apes, including human beings) have evolved the most complex brains on Earth.

Given the evidence that intelligent problem solving skills of various sorts have evolved many times over, along many different evolutionary pathways, in an amazing range of animal groups, one might suspect that Dornhaus believes that human-style cognitive abilities and civilizations are widespread in the universe. In fact, she doesn’t. She thinks that humans with their exaggerated cognitive abilities and unique ability to use language to express complex and novel sorts of information are a quirky and unusual fluke of evolution, and might, for all we know, be wildly improbable. Her argument that alien civilizations probably aren’t widespread resembles one stated by the imminent and influential American evolutionary biologist Ernst Mayr in his 1988 book Towards a New Philosophy of Biology.

There are currently more than 10 million different species of animals on Earth. All but one have failed to evolve the human level of intelligence. This makes the chance of evolving human intelligence less than one in 10 million. Over the last six hundred million years since complex life has appeared on Earth, there have been tens of million different animal species, each existing for roughly 1-10 million years. But, so far as we know, only one of them, Homo sapiens, ever produced a technological society. The human lineage diverged from that of other great ape species about 8 million years ago, but we don’t see evidence of distinctly human innovation until about 50,000 years ago, which is, perhaps, another indication of its rarity.

Despite the apparent improbability of human level intelligence evolving in any one lineage, Earth, as a whole, with its vast array of evolutionary lineages, has nonetheless produced a technological civilization. But that still doesn’t tell us very much. For the present, Earth is the only habitable planet that we know much of anything about. And, since Earth produced us, we are working with a biased sample. So we can’t be at all confident that the presence of human civilization on Earth implies that similar civilizations are likely to occur elsewhere.

For all we know, the quirky set of events that produced human beings might be so wildly improbable that human civilization is unique in a hundred billion galaxies. But, we don’t know for sure that alien civilizations are wildly improbable either. Dornhaus freely concedes that neither she nor anybody has a good idea of just how improbable human intelligence might be, since the evolution of intelligence is still so poorly understood.

Most current evolutionary thinking, following in the footsteps of Mayr and others, holds that human civilization was not the inevitable product of a long-term evolutionary trend, but rather the quirky consequence of a particular and improbable set of evolutionary events. What sort of events might those have been, and just how improbable were they? Dornhaus supports a popular theory proposed by Dr. Geoffrey Miller, an evolutionary psychologist who is an associate professor in the Department of Psychology at the University of New Mexico and who also spoke at the METI institute workshop.

In our next installment we’ll explore Miller’s theories in a bit more detail, and see why the abundance of extraterrestrial civilizations might depend on whether or not aliens think big brains are sexy.

For further reading:
Baluska, F. and Mancuso, S. (2009) Deep evolutionary origins of neurobiology. Communicative and Integrative Biology, 2:1, 60-65.

Chittka, L. and Niven, J. (2009) Are bigger brains better?, Current Biology. 19:21 p. R995-R1008.

Margonelli, L. (2014) Collective mind in the mound: How do termites build their huge structures. National Geographic.

Mayr, E. (1988) The probability of extraterrestrial intelligent life. In Towards a New Philosophy of Biology, Harvard University Press, Cambridge, MA.

Patton, P. E. (2015) Who speaks for Earth? The controversy over interstellar messaging. Universe Today.

P. Patton (2014) Communicating across the cosmos, Part 1: Shouting into the darkness, Part 2: Petabytes from the Stars, Part 3: Bridging the Vast Gulf, Part 4: Quest for a Rosetta Stone, Universe Today.

Tonn, S. (2015) Termites are teaching architects to design super-efficient skyscrapers. Wired Magazine.

October 2, 2015December 23, 2015 by Paul Patton

Is There a Kraken in Kraken Mare? What Kind of Life Would We Find on Titan?

The left image shows a mosaic of images of Titan taken by the Cassini spacecraft in near infrared light. Titan’s polar seas are visible as sunlight glints off of them. The right image is a radar image of Kraken Mare. Credit: NASA Jet Propulsion Laboratory.

Could there be life on Saturn’s large moon Titan? Asking the question forces astrobiologists and chemists to think carefully and creatively about the chemistry of life, and how it might be different on other worlds than it is on Earth. In February, a team of researchers from Cornell University, including chemical engineering graduate student James Stevenson, planetary scientist Jonathan Lunine, and chemical engineer Paulette Clancy, published a pioneering study arguing that cell membranes could form under the exotic chemical conditions present on this remarkable moon.

In many ways, Titan is Earth’s twin. It’s the second largest moon in the solar system and bigger than the planet Mercury. Like Earth, it has a substantial atmosphere, with a surface atmospheric pressure a bit higher than Earth’s. Besides Earth, Titan is the only object in our solar system known to have accumulations of liquid on its surface. NASA’s Cassini space probe discovered abundant lakes and even rivers in Titan’s polar regions. The largest lake, or sea, called Kraken Mare, is larger than Earth’s Caspian Sea. Researchers know from both spacecraft observations and laboratory experiments that Titan’s atmosphere is rich in complex organic molecules, which are the building blocks of life.

All these features might make it seem as though Titan is tantalizingly suitable for life. The name ‘Kraken’, which refers to a legendary sea monster, fancifully reflects the eager hopes of astrobiologists. But, Titan is Earth’s alien twin. Being almost ten times further from the sun than Earth is, its surface temperature is a frigid -180 degrees Celsius. Liquid water is vital to life as we know it, but on Titan’s surface all water is frozen solid. Water ice takes on the role that silicon-containing rock does on Earth, making up the outer layers of the crust.

The liquid that fills Titan’s lakes and rivers is not water, but liquid methane, probably mixed with other substances like liquid ethane, all of which are gases here on Earth. If there is life in Titan’s seas, it is not life as we know it. It must be an alien form of life, with organic molecules dissolved in liquid methane instead of liquid water. Is such a thing even possible?

The Cornell team took up one key part of this challenging question by investigating whether cell membranes can exist in liquid methane. Every living cell is, essentially, a self-sustaining network of chemical reactions, contained within bounding membranes. Scientists think that cell membranes emerged very early in the history of life on Earth, and their formation might even have been the first step in the origin of life.

Here on Earth, cell membranes are as familiar as high school biology class. They are made of large molecules called phospholipids. Each phospholipid molecule has a ‘head’ and a ‘tail’. The head contains a phosphate group, with a phosphorus atom linked to several oxygen atoms. The tail consists of one or more strings of carbon atoms, typically 15 to 20 atoms long, with hydrogen atoms linked on each side. The head, due to the negative charge of its phosphate group, has an unequal distribution of electrical charge, and we say that it is polar. The tail, on the other hand, is electrically neutral.

phospholipid membrane — Here on Earth, cell membranes are composed of phospholipid molecules dissolved in liquid water. A phospholipid has a backbone of carbon atoms (gray), and also contains hydrogen (sky blue), phosphorus (yellow), oxygen (red), and nitrogen (blue). Due to the positive charge associated with the nitrogen containing choline group, and the negative charge associated with the phosphate group, the head is polar, and attracts water. It is therefore hydrophilic. The hydrocarbon tail is electrically neutral and hydrophobic. The structure of a cell membrane is due these electrical properties of phospholipids and water. The molecules form a double layer, with the hydrophilic heads facing outward, towards water, and the hydrophobic tails facing inward, towards one another. Credit: Ties van Brussel

These electrical properties determine how phospholipid molecules will behave when they are dissolved in water. Electrically speaking, water is a polar molecule. The electrons in the water molecule are more strongly attracted to its oxygen atom than to its two hydrogen atoms. So, the side of the molecule where the two hydrogen atoms are has a slight positive charge, and the oxygen side has a small negative charge. These polar properties of water cause it to attract the polar head of the phospholipid molecule, which is said to be hydrophilic, and repel its nonpolar tail, which is said to be hydrophobic.

When phospholipid molecules are dissolved in water, the electrical properties of the two substances work together to cause the phospholipid molecules to organize themselves into a membrane. The membrane closes onto itself into a little sphere called a liposome. The phospholipid molecules form a bilayer two molecules thick. The polar hydrophilic heads face outward towards the water on both the inner and outer surface of the membrane. The hydrophobic tails are sandwiched between, facing each other. While the phospholipid molecules remain fixed in their layer, with their heads facing out and their tails facing in, they can still move around with respect to each other, giving the membrane the fluid flexibility needed for life.

Phospholipid bilayer membranes are the basis of all terrestrial cell membranes. Even on its own, a liposome can grow, reproduce and aid certain chemical reactions important to life, which is why some biochemists think that the formation of liposomes might have been the first step towards life. At any rate, the formation of cell membranes must surely been an early step in life’s emergence on Earth.

water and methane — At the left, water, consisting of hydrogen (H) and oxygen (O), is a polar solvent. Oxygen attracts electrons more strongly than hydrogen does, giving the hydrogen side of the molecule a net positive charge and the oxygen side a net negative charge. The delta symbol ( ) indicates that the charge is partial, that is less than a full unit of positive or negative charge. At right, methane is a non-polar solvent, due to the symmetrical distribution of hydrogen atoms (H) around a central carbon atom (C). Credit: Jynto as modified by Paul Patton.

If some form of life exists on Titan, whether sea monster or (more likely) microbe, it would almost certainly need to have a cell membrane, just like every living thing on Earth does. Could phospholipid bilayer membranes form in liquid methane on Titan? The answer is no. Unlike water, the methane molecule has an even distribution of electrical charges. It lacks water’s polar qualities, and so couldn’t attract the polar heads of phospholipid molecule. This attraction is needed for the phospholipids to form an Earth-style cell membrane.

Experiments have been conducted where phospholipids are dissolved in non-polar liquids at Earthly room temperature. Under these conditions, the phospholipids form an ‘inside-out’ two layer membrane. The polar heads of the phospholipid molecules are at the center, attracted to one another by their electrical charges. The non-polar tails face outward on each side of the inside-out membrane, facing the non-polar solvent.

membranes in polar and non-polar solvents — At left, phospholipids are dissolved in water, a polar solvent. They form a bilayer membrane, with their polar, hydrophilic heads facing outward towards water, and their hydrophobic tails facing each other. At right, when phospholipids are dissolved in a non-polar solvent at Earthly room temperature, they form an inside-out membrane, with the polar heads attracting one another, and the non-polar tails facing outwards towards the non-polar solvent. Based on figure 2 from Stevenson, Lunine, and Clancy (2015). Credit: Paul Patton

Could Titanian life have an inside out phospholipid membrane? The Cornell team concluded that this wouldn’t work, for two reasons. The first is that at the cryogenic temperatures of liquid methane, the tails of phospholipids become rigid, depriving any inside-out membrane that might form of the fluid flexibility needed for life. The second is that two key ingredients of phospholipids; phosphorus and oxygen, are probably unavailable in the methane lakes of Titan. In their search for Titanian cell membranes, the Cornell team needed to probe beyond the familiar realm of high school biology.

Although not composed of phospholipids, the scientists reasoned that any Titanian cell membrane would nevertheless be like the inside-out phospholipid membranes created in the lab. It would consist of polar molecules clinging together electrically in a solution of non-polar liquid methane. What molecules might those be? For answers the researchers looked to data from the Cassini spacecraft and from laboratory experiments that reproduced the chemistry of Titan’s atmosphere.

Titan’s atmosphere is known to have a very complex chemistry. It is made mostly of nitrogen and methane gas. When the Cassini spacecraft analyzed its composition using spectroscopy it found traces of a variety of compounds of carbon, nitrogen, and hydrogen, called nitriles and amines. Researchers have simulated the chemistry of Titan’s atmosphere in the lab by exposing mixtures of nitrogen and methane to sources of energy simulating sunlight on Titan. A stew of organic molecules called ‘tholins’ is formed. It consists of compounds of hydrogen and carbon, called hydrocarbons, as well as nitriles and amines.

The Cornell investigators saw nitriles and amines as potential candidates for their Titanian cell membranes. Both are polar molecules that might stick together to form a membrane in non-polar liquid methane due to the polarity of nitrogen containing groups found in both of them. They reasoned that candidate molecules must be much smaller than phospholipids, so that they could form fluid membranes at liquid methane temperatures. They considered nitriles and amines containing strings of between three and six carbon atoms. Nitrogen containing groups are called ‘azoto’ –groups, so the team named their hypothetical Titanian counterpart to the liposome the ‘azotosome’.

Synthesizing azotosomes for experimental study would have been difficult and expensive, because the experiments would need to be conducted at the cryogenic temperatures of liquid methane. But since the candidate molecules have been studied extensively for other reasons, the Cornell researchers felt justified in turning to the tools of computational chemistry to determine whether their candidate molecules could cohere as a flexible membrane in liquid methane. Computational models have been used successfully to study conventional phospholipid cell membranes.

acrylonitrile — Acrylonitrile has been identified as a possible basis for cell membranes in liquid methane on Titan. It is known to be present in Titan’s atmosphere at a concentration of 10 parts per million and has been produced in laboratory simulations of the effects of energy sources on Titan’s nitrogen-methane atmosphere. As a small polar molecule capable of dissolving in liquid methane, it is a candidate substance for the formation of cell membranes in an alternative biochemistry on Titan. Light blue: carbon atoms, dark blue: nitrogen atom, white: hydrogen atoms. Credit: Ben Mills as modified by Paul Patton.

acrylonitrile membrane — Polar acrylonitrile molecules align ‘head’ to ‘tail’ to form a membrane in non-polar liquid methane. Light blue: carbon atoms, dark blue: nitrogen atoms, white: hydrogen atoms. Credit: James Stevenson.

The group’s computational simulations showed that some candidate substances could be ruled out because they would not cohere as a membrane, would be too rigid, or would form a solid. Nevertheless, the simulations also showed that a number of substances would form membranes with suitable properties. One suitable substance is acrylonitrile, which Cassini showed is present in Titan’s atmosphere at 10 parts per million concentration. Despite the huge difference in temperature between cryogenic azotozomes and room temperature liposomes, the simulations showed them to exhibit strikingly similar properties of stability and response to mechanical stress. Cell membranes, then, are possible for life in liquid methane.

Computational chemistry simulations show that acrylonitrile and some other small polar nitrogen containing organic molecules are capable of forming ‘azotosomes’ when they are dissolved on liquid methane. Azotosomes are small membrane bounded spherules like the liposomes formed by phospholipids when they are dissolved in water. The simulations show that acrylonitrile azotosomes would be both stable and flexible in cryogenically cold liquid methane, giving them the properties they need to function as cell membranes for hypothetical Titanian life, or for life on any world with liquid methane on its surface. The azotosome shown is 9 nanometers in size, about the size of a virus. Light blue: carbon atoms, dark blue: nitrogen atoms, white: hydrogen atoms. Credit: James Stevenson.

The scientists from Cornell view their findings as nothing more than a first step towards showing that life in liquid methane is possible, and towards developing the methods that future spacecraft will need to search for it on Titan. If life is possible in liquid methane, the implications ultimately extend far beyond Titan.

When seeking conditions suitable for life in the galaxy, astronomers typically search for exoplanets within a star’s habitable zone, defined as the narrow range of distances over which a planet with an Earth-like atmosphere would have a surface temperature suitable for liquid water. If methane life is possible, then stars would also have a methane habitable zone, a region where methane could exist as a liquid on a planet or moon, making methane life possible. The number of habitable worlds in the galaxy would be greatly increased. Perhaps, on some worlds, methane life evolves into complex forms that we can scarcely imagine. Maybe some of them are even a bit like sea monsters.

References and Further Reading:

N. Atkinson (2010) Alien Life on Titan? Hang on Just a Minute, Universe Today.

N. Atkinson (2010) Life on Titan Could be Smelly and Explosive, Universe Today.

M. L. Cable, S. M. Horst, R. Hodyss, P. M. Beauchamp, M. A. Smith, P. A. Willis, (2012) Titan tholins: Simulating Titan organic chemistry in the Cassini-Huygens era, Chemical Reviews, 112:1882-1909.

E. Howell (2014) Titan’s Majestic Mirror-Like Lakes Will Come Under Cassini’s Scrutiny This Week, Universe Today.

J. Major (2013) Titan’s North Pole is Loaded With Lakes, Universe Today.

C. P. McKay, H. D. Smith, (2005) Possibilities for methanogenic life in liquid methane on the surface of Titan, Icarus 178: 274-276.

J. Stevenson, J. Lunine, P. Clancy, (2015) Membrane alternatives in worlds without oxygen: Creation of an azotosome, Science Advances 1(1):e1400067.

S. Oleson (2014) Titan submarine: Exploring the depths of Kraken, NASA Glenn Research Center, Press release.

Cassini Solstice Mission, NASA Jet Propulsion Laboratory

NASA and ESA celebrate 10 years since Titan landing, NASA 2015

August 18, 2015December 23, 2015 by Nancy Atkinson

More Evidence That Comets May Have Brought Life to Earth

Halleys Comet, as seen in May 1986. Credit and copyright: Bob King.

The idea of panspermia — that life on Earth originated from comets or asteroids bombarding our planet — is not new. But new research may have given the theory a boost. Scientists from Japan say their experiments show that early comet impacts could have caused amino acids to change into peptides, becoming the first building blocks of life. Not only would this help explain the genesis of life on Earth, but it could also have implications for life on other worlds.

Dr. Haruna Sugahara, from the Japan Agency for Marine-Earth Science and Technology in Yokahama, and Dr. Koichi Mimura, from Nagoya University said they conducted “shock experiments on frozen mixtures of amino acid, water ice and silicate (forsterite) at cryogenic condition (77 K),” according to their paper. “In the experiments, the frozen amino acid mixture was sealed into a capsule … a vertical propellant gun was used to [simulate] impact shock.”

They analyzed the post-impact mixture with gas chromatography, and found that some of the amino acids had joined into short peptides of up to 3 units long (tripeptides).

Based on the experimental data, the researchers were able to estimate that the amount of peptides produced would be around the same as had been thought to be produced by normal terrestrial processes (such as lighting storms or hydration and dehydration cycles).

Artists concept of the stardust spacecraft flying throug the gas and dust from comet Wild 2. Credit: NASA/JPL

“This finding indicates that comet impacts almost certainly played an important role in delivering the seeds of life to the early Earth,” said Sugahara. “It also opens the likelihood that we will have seen similar chemical evolution in other extraterrestrial bodies, starting with cometary-derived peptides.”

The earliest known fossils on Earth are from about 3.5 billion years ago and there is evidence that biological activity took place even earlier. But there’s evidence that early Earth had little water and carbon-based molecules on the Earth’s surface, so how could these building blocks of life delivered to the Earth’s surface so quickly? This was also about the time of the Late Heavy Bombardment, and so the obvious answer could be the collision of comets and asteroids with the Earth, since these objects contain abundant supplies of both water and carbon-based molecules.

A view of NASA's Deep Impact probe colliding with comet Tempel 1, captured by the Deep Impact flyby spacecraft's high-resolution instrument. — A view of NASA’s Deep Impact probe colliding with comet Tempel 1, captured by the Deep Impact flyby spacecraft’s high-resolution instrument.

Space missions to comets are helping to confirm this possibility. The 2004 Stardust mission found the amino acid when it collected particles from Comet Wild 2. When NASA’s Deep Impact spacecraft crashed into Comet Tempel 1 in 2005, it discovered a mixture of organic and clay particles inside the comet. One theory about the origins of life is that clay particles act as a catalyst, allowing simple organic molecules to get arranged into more and more complex structures.

The news from the current Rosetta mission to comet 67P/Churyumov-Gerasimenko also indicates that comets are a rich source of materials, and more discoveries are likely to be forthcoming from that mission.

Jets of gas and dust are blasting from the active neck of comet 67P/Churyumov-Gerasimenko in this photo mosaic assembled from four images taken on 26 September 2014 by the European Space Agency’s Rosetta spacecraft at a distance of 26.3 kilometers (16 miles) from the center of the comet. Credit: ESA/Rosetta/NAVCAM/Marco Di Lorenzo/Ken Kremer/kenkremer.com

“Two key parts to this story are how complex molecules are initially generated on comets and then how they survive/evolve when the comet hits a planet like the Earth,” said Professor Mark Burchell from the University of Kent in the UK, commenting on the new research from Japan. “Both of these steps can involve shocks which deliver energy to the icy body… building on earlier work, Dr. Sugahara and Dr. Mimura have shown how amino acids on icy bodies can be turned into short peptide sequences, another key step along the path to life.”

“Comet impacts are normally associated with mass extinction on Earth, but this works shows that they probably helped kick-start the whole process of life in the first place,” said Sugahara. “The production of short peptides is the key step in the chemical evolution of complex molecules. Once the process is kick-started, then much less energy is needed to make longer chain peptides in a terrestrial, aquatic environment.”

The scientists also indicated that similar “kickstarting” could have happened in other places in our Solar System, such as on the icy moons Europa and Enceladus, as they likely underwent a similar comet bombardment.

Sugahara and Mimura presented their findings at the Goldschmidt geochemistry conference in Prague, going on this week.

April 8, 2015February 7, 2022 by Paul Patton

Beyond “Fermi’s Paradox” II: Questioning the Hart-Tipler Conjecture

Artist's impression of The Milky Way Galaxy. Based on current estimates and exoplanet data, it is believed that there could be tens of billions of habitable planets out there. Credit: NASA

Welcome back to our Fermi Paradox series, where we take a look at possible resolutions to Enrico Fermi’s famous question, “Where Is Everybody?” Today, we examine the possibility that the reason we’ve found no evidence of alien civilizations is because there are none out there.

It’s become a legend of the space age. The brilliant physicist Enrico Fermi, during a lunchtime conversation at Los Alamos National Laboratory in 1950, is supposed to have posed a conundrum for proponents of the existence of extraterrestrial civilizations.

If space traveling aliens exist, so the argument goes, they would spread through the galaxy, colonizing every habitable world. They should then have colonized Earth. They should be here, but because they aren’t, they must not exist.

This is the argument that has come to be known as “Fermi’s paradox”. The problem is, as we saw in the first installment, Fermi never made it. As his surviving lunch companions recall (Fermi himself died of cancer just four years later, and never published anything on the topic of extraterrestrial intelligence), he simply raised a question, “Where is everybody?” to which there are many possible answers.

April 7, 2015February 7, 2022 by Paul Patton

Beyond “Fermi’s Paradox” I: A Lunchtime Conversation- Enrico Fermi and Extraterrestrial Intelligence

Nuclear physicist Enrico Fermi won the 1938 Nobel Prize for a technique he developed to probe the atomic nucleus. He led the team that developed the world's first nuclear reactor, and played a central role in the Manhattan Project that developed the atomic bomb during World War II. In the debate over extraterrestrial intelligence, he is best known for posing the question 'Where is everybody?' during a lunchtime discussion at Los Alamos National Laboratory. His question was seen as the basis for the "Fermi Paradox". Credit: Smithsonian Institution Archives.

Welcome back to our Fermi Paradox series, where we take a look at possible resolutions to Enrico Fermi’s famous question, “Where Is Everybody?” Today, we examine the lunchtime conversation that started it all!

It’s become a kind of legend, like Newton and the apple or George Washington and the cherry tree. One day in 1950, the great physicist Enrico Fermi sat down to lunch with colleagues at the Fuller Lodge at Los Alamos National Laboratory in New Mexico and came up with a powerful argument about the existence of extraterrestrial intelligence, the so-called “Fermi paradox”.

But like many legends, it’s only partly true. Robert Gray explained the real history in a recent paper in the journal Astrobiology. Enrico Fermi was the winner of the 1938 Nobel Prize for physics, led the team that developed the world’s first nuclear reactor at the University of Chicago, and was a key contributor to the Manhattan Project that developed the atomic bomb during World War II. The Los Alamos Lab where he worked was founded as the headquarters of that project.

February 19, 2015June 5, 2018 by Paul Patton

Who Speaks for Earth? The Controversy over Interstellar Messaging

The prospect of alien invasion has sent shivers down the spines of science fiction fans ever since H. G. Wells published his classic “The War of the Worlds” in 1897. Drawing on the science of his times, Wells envisioned Mars as an arid dying world, whose inhabitants coveted the lush blue Earth. Wells’ portrayal of Martian imperialism had a political message. As an opponent of British colonialism, he wanted his countrymen to imagine what colonialism would be like from the other side. Although opponents of METI seldom explicitly invoke the spectre of alien invasion, some do view the human history of colonialism as a possible model for how aliens might treat us. The eminent physicist Stephen Hawking warned that “If aliens visit us, the outcome would be much as when Columbus landed in America, which didn’t turn our well for the Native Americans”. The illustration from Well’s novel shows a Martian fighting machine attacking the British warship HMS Thunderchild. (credit: Henrique Alvim Correa, 1906, for the novel “The War of the Worlds”)

Should we beam messages into deep space, announcing our presence to any extraterrestrial civilizations that might be out there? Or, should we just listen? Since the beginnings of the modern Search for Extraterrestrial Intelligence (SETI), radio astronomers have, for the most part, followed the listening strategy.

In 1999, that consensus was shattered. Without consulting with other members of the community of scientists involved in SETI, a team of radio astronomers at the Evpatoria Radar Telescope in Crimea, led by Alexander Zaitsev, beamed an interstellar message called ‘Cosmic Call’ to four nearby sun-like stars. The project was funded by an American company called Team Encounter and used proceeds obtained by allowing members of the general public to submit text and images for the message in exchange for a fee.

Similar additional transmissions were made from Evpatoria in 2001, 2003, and 2008. In all, transmissions were sent towards twenty stars within less than 100 light years of the sun. The new strategy was called Messaging to Extraterrestrial Intelligence (METI). Although Zaitsev was not the first to transmit an interstellar message, he and his associates where the first to systematically broadcast to nearby stars. The 70 meter radar telescope at Evpatoria is the second largest radar telescope in the world.

In the wake of the Evpatoria transmissions a number of smaller former NASA tracking and research stations collected revenue by making METI transmissions as commercially funded publicity stunts. These included a transmission in the fictional Klingon language from Star Trek to promote the premier of an opera, a Dorito’s commercial, and the entirety of the 2008 remake of the classic science fiction movie “The Day the Earth Stood Still”. The specifications of these commercial signals have not been made public, but they were most likely much too faint to be detectable at interstellar distances with instruments comparable to those possessed by humans.

Zaitsev’s actions stirred divisive controversy among the community of scientists and scholars concerned with the field. The two sides of the debate faced off in a recent special issue of the Journal of the British Interplanetary Society, resulting from a live debate sponsored in 2010 by the Royal Society at Buckinghamshire, north of London, England.

Alexander L. Zaitsev- Chief scientist of the Russian Academy of Science’s Institute of Radio Engineering and Electronics, and head of the group that transmitted interstellar messages using the Evpatoria Planetary Radar telescope. (credit: Rumin)

Modern SETI got its start in 1959, when astrophysicists Giuseppe Cocconi and Phillip Morrison published a paper in the prestigious scientific journal Nature, in which they showed that the radio telescopes of the time were capable of receiving signals transmitted by similar counterparts at the distances of nearby stars. Just months later, radio astronomer Frank Drake turned an 85 foot radio telescope dish towards two nearby sun-like stars and conducted Project Ozma, the first SETI listening experiment. Morrison, Drake, and the young Carl Sagan supposed that extraterrestrial civilizations would “do the heavy lifting” of establishing powerful and expensive radio beacons announcing their presence. Humans, as cosmic newcomers that had just invented radio telescopes, should search and listen. There was no need to take the risk, however small, of revealing our presence to potentially hostile aliens.

Drake and Sagan did indulge in one seeming exception to their own moratorium. In 1974, the pair devised a brief 1679 bit message that was transmitted from the giant Arecibo Radar Telescope in Puerto Rico. But the transmission was not a serious attempt at interstellar messaging. By intent, it was aimed at a vastly distant star cluster 25,000 light years away. It merely served to demonstrate the new capabilities of the telescope at a rededication ceremony after a major upgrade.

In the 1980’s and 90’s SETI researchers and scholars sought to formulate a set of informal rules for the conduct of their research. The First SETI Protocol specified that any reply to a confirmed alien message must be preceded by international consultations, and an agreement on the content of the reply. It was silent on the issue of transmissions sent prior to the discovery of an extraterrestrial signal.

David Brin- Space scientist, futurist consultant, and science fiction writer (credit: Glogger)

A Second SETI Protocol was to have addressed the issue, but, somewhere along the way, critics charge, something went wrong. David Brin, a space scientist, futurist consultant, and science fiction writer was a participant in the protocol discussion. He charged that “collegial discussion started falling apart” and “drastic alterations of earlier consensus agreements were rubber-stamped, with the blatant goal of removing all obstacles from the path of those pursuing METI”.

Brin accuses “the core community that clusters around the SETI Institute in Silicon Valley, California”, including astronomers Jill Tartar and Seth Shostak of “running interference for and enabling others around the world- such as Russian radio astronomer Dr. Alexander Zaitsev” to engage in METI efforts. Shostak denies this, and claims he simply sees no clear criteria for regulating such transmissions.

Brin, along with Michael A. G. Michaud, a former U.S. Foreign Service Officer and diplomat who chaired the committee that formulated the first and second protocol, and John Billingham, the former head of NASA’s short lived SETI effort, resigned their memberships in SETI related committees to protest the alterations to the second protocol.

The founders of SETI felt that extraterrestrial intelligence was likely to be benign. Carl Sagan speculated that extraterrestrial civilizations (ETCs) older than ours would, under the pressure of necessity, become peaceful and environmentally responsible, because those that didn’t would self-destruct. Extraterrestrials, they supposed, would engage in interstellar messaging because of a wish to share their knowledge and learn from others. They supposed that ETCs would establish powerful omnidirectional beacons in order to assist others in finding them and joining a communications network that might span the galaxy. Most SETI searches have been optimized for detecting such steady constantly transmitting beacons.

Over the fifty years since the beginnings of SETI, searches have been sporadic and plagued with constant funding problems. The space of possible directions, frequencies, and coding strategies has only barely been sampled so far. Still, David Brin contends that whole swaths of possibilities have been eliminated “including gaudy tutorial beacons that advanced ETCs would supposedly erect, blaring helpful insights to aid all newcomers along the rocky paths”. The absence of obvious, easily detectable evidence of extraterrestrial intelligence has led some to speak of the “Great Silence”. Something, Brin notes, “has kept the prevalence and visibility of ETCs below our threshold of observation”. If alien civilizations are being quiet, could it be that they know something that we don’t know about some danger?

Alexander Zaitsev thinks that such fears are unfounded, but that other civilizations might suffer from the same reluctance to transmit that he sees as plaguing humanity. Humanity, he thinks, should break the silence by beaming messages to its possible neighbors. He compares the current state of humanity to that of a man trapped in a one-man prison cell. “We”, he writes “do not want to live in a cocoon, in a ‘one –man cell’, without any rights to send a message outside, because such a life is not INTERESTING! Civilizations forced to hide and tremble because of farfetched fears are doomed to extinction”. He notes that in the ‘60’s astronomer Sebastian von Hoerner speculated that civilizations that don’t engage in interstellar communication eventually decline through “loss of interest”.

METI critics maintain that questions of whether or not to send powerful, targeted, narrowly beamed interstellar transmissions, and of what the content of those transmissions should be needs to be the subject of broad international and public discussion. Until such discussion has taken place, they want a temporary moratorium on such transmissions.

Seth Shostak- SETI Institute radio astronomer (credit: B D Engler)

On the other hand, SETI Institute radio astronomer Seth Shostak thinks that such deliberations would be pointless. Signals already leak into space from radio and television broadcasting, and from civilian and military radar. Although these signals are too faint to be detected at interstellar distances with current human technology, Shostak contends that with the rapid growth in radio telescope technology, ETCs with technology even a few centuries in advance of ours could detect this radio leakage. Billingham and Benford counter that to collect enough energy to tune in on such leakage; an antenna with a surface area of more than 20,000 square kilometers would be needed. This is larger than the city of Chicago. If humans tried to construct such a telescope with current technology it would cost 60 trillion dollars.

Shostak argues that exotic possibilities might be available to a very technologically advanced society. If a telescope were placed at a distance of 550 times the Earth’s distance from the sun, it would be in a position to use the sun’s gravitational field as a gigantic lens. This would give it an effective collecting area vastly larger than the city of Chicago, for free. If advanced extraterrestrials made use of their star’s gravitational field in this way, Shostak maintains “that would give them the capacity to observe many varieties of terrestrial transmissions, and in the optical they would have adequate sensitivity to pick up the glow of street lamps”. Even Brin conceded that this idea was “intriguing”.

Civilizations in a position to do us potential harm through interstellar travel, Shostak contends, would necessarily be technologically advanced enough to have such capabilities. “We cannot pretend that our present level of activity with respect to broadcasting or radar usage is ‘safe’. If danger exists, we’re already vulnerable” he concludes. With no clear means to say what extraterrestrials can or can’t detect, Shostak feels the SETI community has nothing concrete to contribute to the regulation of radio transmissions.

Could extraterrestrials harm us? In 1897 H. G. Wells published his science fiction classic “The War of the Worlds” in which Earth was invaded by Martians fleeing their arid, dying world. Besides being scientifically plausible in terms of its times, Wells’ novel had a political message. An opponent of British colonialism, he wanted his countrymen to imagine what imperialism was like from the other side. Tales of alien invasion have been a staple of science fiction ever since. Some still regard European colonialism as a possible model for how extraterrestrials might treat humanity. The eminent physicist Steven Hawking thinks very advanced civilizations might have mastered interstellar travel. Hawking warned that “If aliens visit us, the outcome would be much as when Columbus landed in America, which didn’t turn out well for the Native Americans”.

Though dismissing Hawking’s fears of alien invasion as an “unlikely speculation”, David Brin notes that interstellar travel by small automated probes is quite feasible, and that such a probe could potentially do harm to us in many ways. It might, for example, steer an asteroid onto a collision course with Earth. A relatively small projectile traveling at one tenth the speed of light could wreak terrible damage by simply colliding with our planet. “The list of unlikely, but physically quite possible scenarios is very long” he warns.

Diplomat Michael Michaud warns that “We can all understand the frustration of not finding any signals after fifty years of intermittent searching” but “Impatience with the search is not a sufficient justification for introducing a new level of potential risk for our entire species”.

METI critics David Brin, James Benford, and James Billingham think that the current lack of results from SETI warrants a different sort of response than METI. They call for a reassessment of the search strategy. From the outset, SETI researchers have assumed that extraterrestrials will use steady beacons transmitting constantly in all directions to attract our attention. Recent studies of interstellar radio propagation and the economics of signaling show that such a beacon, which would need to operate on a vast timescale, is not an efficient way to signal.

Instead, an alien civilization might compile a list of potentially habitable worlds in its neighborhood and train a narrowly beamed signal on each member of the list in succession. Such brief “ping” messages might be repeated, in sequence, once a year, once a decade, or once a millennium. Benford and Billingham note that most SETI searches would miss this sort of signal.

The SETI Institute’s Allen telescope array, for example, is designed to target narrow patches of sky (such as the space around a sun-like star) and search those patches in sequence, for the presence of continuously transmitting beacons. It would miss a transient “ping” signal, because it would be unlikely to be looking in the right place at the right time. Ironically, the Evpatoria messages, transmitted for less than a day, are examples of such transient signals.

Benford and Billingham propose the construction of a new radio telescope array designed to constantly monitor the galactic plane (where stars are most abundant) for transient signals. Such a telescope array, they estimate, would cost about 12 million dollars, whereas a serious, sustained METI program would cost billions.

The METI controversy continues. On February 13, the two camps debated each other at the American Association for the Advancement of Science conference in San Jose, California. At that conference David Brin commented “It’s an area where opinion rules, and everyone has a fierce opinion”. In the wake of the meeting a group of 28 scientists, scholars, and business leaders issued a statement that “We feel the decision whether or not to transmit must be based on a worldwide consensus, and not a decision based on the wishes of a few individuals with access to powerful communications equipment”.

References and Further Reading:

J. Benford, J. Billingham, D. Brin, S. Dumas, M. Michaud, S. Shostak, A. Zaitsev, (2014) Messaging to Extraterrestrial Intelligence special section, Journal of the British Interplanetary Society, 67, p. 5-43.

The SETI Institute

D. Brin, Shouting at the cosmos: How SETI has taken a worrisome turn into dangerous territory.

F. Cain (2013) How could we find aliens? The search for extraterrestrial intelligence (SETI), Universe Today.

E. Hand (2015), Researchers call for interstellar messages to alien civilizations, Science Insider, Science Magazine.

January 6, 2015December 23, 2015 by Paul Patton

Defining Life II: Metabolism and Evolution as clues to Extraterrestrial Life

The James Webb Space Telescope, scheduled for launch in 2018 may be the first to be capable of detecting biomarker gasses in the atmospheres of extrasolar planets. When an exoplanet passes between its star and Earth, an event called a transit, light that has passed through the planet’s atmosphere can be detected from a vantage point near Earth. When light passes through the exoplanet’s atmosphere, some wavelengths are absorbed and others transmitted. By analyzing the transmitted light spectrum, astronomers can learn the composition of the planet’s atmosphere. Astrobiologists hope to find biomarker gasses indicating the metabolic waste products of life. The oxygen in Earth’s atmosphere is a waste product of photosynthesis in plants and bacteria. The Webb telescope may be capable of conducting this test for planets larger than Earth (super-earths) transiting small stars. Space telescopes capable of conducting such research on a larger scale have been delayed by budget cuts. Credit: NASA

In the movie “Avatar”, we could tell at a glance that the alien moon Pandora was teeming with alien life. Here on Earth though, the most abundant life is not the plants and animals that we are familiar with. The most abundant life is simple and microscopic. There are 50 million bacterial organisms in a single gram of soil, and the world wide bacterial biomass exceeds that of all plants and animals. Microbes can grow in extreme environments of temperature, salinity, acidity, radiation, and pressure. The most likely form in which we will encounter life elsewhere in our solar system is microbial.

Astrobiologists need strategies for inferring the presence of alien microbial life or its fossilized remains. They need strategies for inferring the presence of alien life on the distant planets of other stars, which are too far away to explore with spacecraft in the foreseeable future. To do these things, they long for a definition of life, that would make it possible to reliably distinguish life from non-life.

Unfortunately, as we saw in the first installment of this series, despite enormous growth in our knowledge of living things, philosophers and scientists have been unable to produce such a definition. Astrobiologists get by as best they can with definitions that are partial, and that have exceptions. Their search is geared to the features of life on Earth, the only life we currently know.

In the first installment, we saw how the composition of terrestrial life influences the search for extraterrestrial life. Astrobiologists search for environments that once contained or currently contain liquid water, and that contain complex molecules based on carbon. Many scientists, however, view the essential features of life as having to do with its capacities instead of its composition.

In 1994, a NASA committee adopted a definition of life as a “self-sustaining chemical system capable of Darwinian evolution”, based on a suggestion by Carl Sagan. This definition contains two features, metabolism and evolution, that are typically mentioned in definitions of life.

Metabolism is the set of chemical processes by which living things actively use energy to maintain themselves, grow, and develop. According to the second law of thermodynamics, a system that doesn’t interact with its external environment will become more disorganized and uniform with time. Living things build and maintain their improbable, highly organized state because they harness sources of energy in their external environment to power their metabolism.

Plants and some bacteria use the energy of sunlight to manufacture larger organic molecules out of simpler subunits. These molecules store chemical energy that can later be extracted by other chemical reactions to power their metabolism. Animals and some bacteria consume plants or other animals as food. They break down complex organic molecules in their food into simpler ones, to extract their stored chemical energy. Some bacteria can use the energy contained in chemicals derived from non-living sources in the process of chemosynthesis.

In a 2014 article in Astrobiology, Lucas John Mix, a Harvard evolutionary biologist, referred to the metabolic definition of life as Haldane Life after the pioneering physiologist J. B. S. Haldane. The Haldane life definition has its problems. Tornadoes and vorticies like Jupiter’s Great Red Spot use environmental energy to sustain their orderly structure, but aren’t alive. Fire uses energy from its environment to sustain itself and grow, but isn’t alive either.

Despite its shortcomings, astrobiologists have used Haldane definition to devise experiments. The Viking Mars landers made the only attempt so far to directly test for extraterrestrial life, by detecting the supposed metabolic activities of Martian microbes. They assumed that Martian metabolism is chemically similar to its terrestrial counterpart.

One experiment sought to detect the metabolic breakdown of nutrients into simpler molecules to extract their energy. A second aimed to detect oxygen as a waste product of photosynthesis. A third tried to show the manufacture of complex organic molecules out of simpler subunits, which also occurs during photosynthesis. All three experiments seemed to give positive results, but many researchers believe that the detailed findings can be explained without biology, by chemical oxidizing agents in the soil.

Viking Lander — In 1976, two Viking spacecraft landed on Mars. The image is of a model of the Viking lander, along with astronomer and pioneering astrobiologist Carl Sagan. Each lander was equipped with life detection experiments designed to detect life based on its metabolic activities. These activities were assumed to be chemically similar to those of Earthly organisms. The three experiments included: 1) The labeled release experiment, in which radioactively labeled organic nutrients were added to Martian soil. If organisms were present, it was assumed that their metabolism would involve breaking down the nutrients for their energy content and releasing labeled carbon dioxide as a waste product. 2) The gas exchange experiment, in which Martian soil was provided with nutrients and light and monitored for the release of oxygen. On Earth, organisms that capture the energy of sunlight through the process of photosynthesis, like plants and some bacteria, release oxygen as a waste product. 3) The pyrolytic release experiment, in which Martian soil was placed in a chamber with radioactively labeled carbon dioxide. If there were organisms in the soil that photosynthesized like those on Earth, their metabolic processes would take up the gas and use the energy of sunlight to manufacture more complex organic molecules. Radioactive carbon would be given off when those more complex molecules were broken down by heating the sample. All three experiments produced what seemed like positive results. However, most scientists rejected this interpretation because the details of many of the results could be explained by supposing that there were chemical oxidizing agents in the soil instead of life, and because Viking failed to detect organic materials in Martian soil. This interpretation, especially for the labeled release experiment, remains controversial to this day and may need to be revisited based on recent findings.
Credits: NASA/Jet Propulsion Laboratory, Caltech

Some of the Viking results remain controversial to this day. At the time, many researchers felt that the failure to find organic materials in Martian soil ruled out a biological interpretation of the metabolic results. The more recent finding that Martian soil actually does contain organic molecules that might have been destroyed by perchlorates during the Viking analysis, and that liquid water was once abundant on the surface of Mars lend new plausibility to the claim that Viking may have actually succeeded in detecting life. By themselves, though, the Viking results didn’t prove that life exists on Mars nor rule it out.

The metabolic activities of life may also leave their mark on the composition of planetary atmospheres. In 2003, the European Mars Express spacecraft detected traces of methane in the Martian atmosphere. In December 2014, a team of NASA scientists reported that the Curiosity Mars rover had confirmed this finding by detected atmospheric methane from the Martian surface.

Most of the methane in Earth’s atmosphere is released by living organisms or their remains. Subterranean bacterial ecosystems that use chemosynthesis as a source of energy are common, and they produce methane as a metabolic waste product. Unfortunately, there are also non-biological geochemical processes that can produce methane. So, once more, Martian methane is frustratingly ambiguous as a sign of life.

Extrasolar planets orbiting other stars are far too distant to visit with spacecraft in the foreseeable future. Astrobiologists still hope to use the Haldane definition to search for life on them. With near future space telescopes, astronomers hope to learn the composition of the atmospheres of these planets by analyzing the spectrum of light wavelengths reflected or transmitted by their atmospheres. The James Webb Space Telescope scheduled for launch in 2018, will be the first to be useful in this project. Astrobiologists want to search for atmospheric biomarkers; gases that are metabolic waste products of living organisms.

Once more, this quest is guided by the only example of a life-bearing planet we currently have; Earth. About 21% of our home planet’s atmosphere is oxygen. This is surprising because oxygen is a highly reactive gas that tends to enter into chemical combinations with other substances. Free oxygen should quickly vanish from our air. It remains present because the loss is constantly being replaced by plants and bacteria that release it as a metabolic waste product of photosynthesis.

Traces of methane are present in Earth’s atmosphere because of chemosynthetic bacteria. Since methane and oxygen react with one another, neither would stay around for long unless living organisms were constantly replenishing the supply. Earth’s atmosphere also contains traces of other gases that are metabolic byproducts.

In general, living things use energy to maintain Earth’s atmosphere in a state far from the thermodynamic equilibrium it would reach without life. Astrobiologists would suspect any planet with an atmosphere in a similar state of harboring life. But, as for the other cases, it would be hard to completely rule out non-biological possibilities.

Besides metabolism, the NASA committee identified evolution as a fundamental ability of living things. For an evolutionary process to occur there must be a group of systems, where each one is capable of reliably reproducing itself. Despite the general reliability of reproduction, there must also be occasional random copying errors in the reproductive process so that the systems come to have differing traits. Finally, the systems must differ in their ability to survive and reproduce based on the benefits or liabilities of their distinctive traits in their environment. When this process is repeated over and over again down the generations, the traits of the systems will become better adapted to their environment. Very complex traits can sometimes evolve in a step-by-step fashion.

Mix named this the Darwin life definition, after the nineteenth century naturalist Charles Darwin, who formulated the theory of evolution. Like the Haldane definition, the Darwin life definition has important shortcomings. It has trouble including everything that we might think of as alive. Mules, for example, can’t reproduce, and so, by this definition, don’t count as being alive.

Despite such shortcomings, the Darwin life definition is critically important, both for scientists studying the origin of life and astrobiologists. The modern version of Darwin’s theory can explain how diverse and complex forms of life can evolve from some initial simple form. A theory of the origin of life is needed to explain how the initial simple form acquired the capacity to evolve in the first place.

The chemical systems or life forms found on other planets or moons in our solar system might be so simple that they are close to the boundary between life and non-life that the Darwin definition establishes. The definition might turn out to be vital to astrobiologists trying to decide whether a chemical system they have found really qualifies as a life form. Biologists still don’t know how life originated. If astrobiologists can find systems near the Darwin boundary, their findings may be pivotally important to understanding the origin of life.

Can astrobiologists use the Darwin definition to find and study extraterrestrial life? It’s unlikely that a visiting spacecraft could detect to process of evolution itself. But, it might be capable of detecting the molecular structures that living organisms need in order to take part in an evolutionary process. Philosopher Mark Bedau has proposed that a minimal system capable of undergoing evolution would need to have three things: 1) a chemical metabolic process, 2) a container, like a cell membrane, to establish the boundaries of the system, and 3) a chemical “program” capable of directing the metabolic activities.

Here on Earth, the chemical program is based on the genetic molecule DNA. Many origin-of-life theorists think that the genetic molecule of the earliest terrestrial life forms may have been the simpler molecule ribonucleic acid (RNA). The genetic program is important to an evolutionary process because it makes the reproductive copying process stable, with only occasional errors.

Both DNA and RNA are biopolymers; long chainlike molecules with many repeating subunits. The specific sequence of nucleotide base subunits in these molecules encodes the genetic information they carry. So that the molecule can encode all possible sequences of genetic information it must be possible for the subunits to occur in any order.

Steven Benner, a computational genomics researcher, believes that we may be able to develop spacecraft experiments to detect alien genetic biopolymers. He notes that DNA and RNA are very unusual biopolymers because changing the sequence in which their subunits occur doesn’t change their chemical properties. It is this unusual property that allows these molecules to be stable carriers of any possible genetic code sequence.

DNA and RNA are both polyelectrolytes; molecules with regularly repeating areas of negative electrical charge. Benner believes that this is what accounts for their remarkable stability. He thinks that any alien genetic biopolymer would also need to be a polyelectrolyte, and that chemical tests could be devised by which a spacecraft might detect such polyelectrolyte molecules. Finding the alien counterpart of DNA is a very exciting prospect, and another piece to the puzzle of identifying alien life.

Structure of DNA — Deoxyribonucleic acid (DNA) is the genetic material for all known life on Earth. DNA is a biopolymer consisting of a string of subunits. The subunits consist of nucleotide base pairs containing a purine (adenine A, or guanine G) and a pyrimidine (thymine T, or cytosine C). DNA can contain nucleotide base pairs in any order without its chemical properties changing. This property is rare in biopolymers, and makes it possible for DNA to encode genetic information in the sequence of its base pairs. This stability is due to the fact that each base pair contains phosphate groups (consisting of phosphorus and oxygen atoms) on the outside with a net negative charge. These repeated negative charges make DNA a polyelectrolyte. Computational genomics researcher Steven Benner has hypothesized that alien genetic material will also be a polyelectrolyte biopolymer, and that chemical tests could therefore be devised to detect alien genetic molecules.
Credit: Zephyris

In 1996 President Clinton, made a dramatic announcement of the possible discovery of life on Mars. Clinton’s speech was motivated by the findings of David McKay’s team with the Alan Hills meteorite. In fact, the McKay findings turned out to be just one piece to the larger puzzle of possible Martian life. Unless an alien someday ambles past our waiting cameras, the question of whether or not extraterrestrial life exists is unlikely to be settled by a single experiment or a sudden dramatic breakthrough. Philosophers and scientists don’t have a single, sure-fire definition of life. Astrobiologists consequently don’t have a single sure-fire test that will settle the issue. If simple forms of life do exist on Mars, or elsewhere in the solar system, it now seems likely that that fact will emerge gradually, based on many converging lines of evidence. We won’t really know what we’re looking for until we find it.

References and further reading:

P. S. Anderson (2011) Could Curiosity Determine if Viking Found Life on Mars?, Universe Today.

S. K. Atreya, P. R. Mahaffy, A-S. Wong, (2007), Methane and related trace species on Mars: Origin, loss, implications for life, and habitability, Planetary and Space Science, 55:358-369.

M. A. Bedau (2010), An Aristotelian account of minimal chemical life, Astrobiology, 10(10): 1011-1020.

S. A. Benner (2010), Defining life, Astrobiology, 10(10):1021-1030.

E. Machery (2012), Why I stopped worrying about the definition of life…and why you should as well, Synthese, 185:145-164.

G. M. Marion, C. H. Fritsen, H. Eicken, M. C. Payne, (2003) The search for life on Europa: Limiting environmental factors, potential habitats, and Earth analogs. Astrobiology 3(4):785-811.

L. J. Mix (2015), Defending definitions of life, Astrobiology, 15(1) posted on-line in advance of publication.

P. E. Patton (2014) Moons of Confusion: Why Finding Extraterrestrial Life may be Harder than we Thought, Universe Today.

T. Reyes (2014) NASA’s Curiosity Rover detects Methane, Organics on Mars, Universe Today.

S. Seeger, M. Schrenk, and W. Bains (2012), An astrophysical view of Earth-based biosignature gases. Astrobiology, 12(1): 61-82.

S. Tirard, M. Morange, and A. Lazcano, (2010), The definition of life: A brief history of an elusive scientific endeavor, Astrobiology, 10(10):1003-1009.

C. R. Webster, and numerous other members of the MSL Science team, (2014) Mars methane detection and variability at Gale crater, Science, Science express early content.

Did Viking Mars landers find life’s building blocks? Missing piece inspires new look at puzzle. Science Daily Featured Research Sept. 5, 2010

NASA rover finds active and ancient organic chemistry on Mars, Jet Propulsion laboratory, California Institute of Technology, News, Dec. 16, 2014.

January 5, 2015December 23, 2015 by Paul Patton

Defining Life I: What are Astrobiologists Looking For?

In December, 2014 researchers in the Mars Science Laboratory Project announced that they had made the first definitive detection of organic materials on the surface of Mars. The sample was taken on May 19, 2013 from a rock that mission controllers named “Cumberland”. The Curiosity Mars rover drilled a hole 1.6 cm wide and 6.6 cm deep in the Martian rock. Powered rock from the hole was delivered to the rover’s Sample Analysis at Mars (SAM) instrument for analysis. The scientists drew their conclusions only after months of careful analysis. The identity and complexity of the organic substances remains uncertain, because they may have been altered by perchlorates that were also present in the rock, when the material was heated for analysis. The Viking Mars landers of 1976 had earlier failed to detect organic materials on Mars. Credits: NASA/Jet Propulsion Laboratory, Caltech

How can astrobiologists find extraterrestrial life? In everyday life, we usually don’t have any problem telling that a dog or a rosebush is a living thing and a rock isn’t. In the climatic scene of the movie ‘Europa Report’ we can tell at a glance that the multi-tentacled creature discovered swimming in the ocean of Jupiter’s moon Europa is alive, complicated, and quite possibly intelligent.

But unless something swims, walks, crawls, or slithers past the cameras of a watching spacecraft, astrobiologists face a much tougher job. They need to devise tests that will allow them to infer the presence of alien microbial life from spacecraft data. They need to be able to recognize fossil traces of past alien life. They need to be able to determine whether the atmospheres of distant planets circling other stars contain the tell-tale traces of unfamiliar forms of life. They need ways to infer the presence of life from knowledge of its properties. A definition of life would tell them what those properties are, and how to look for them. This is the first of a two part series exploring how our concept of life influences the search for extraterrestrial life.

What is it that sets living things apart? For centuries, philosophers and scientists have sought an answer. The philosopher Aristotle (384-322 BC) devoted a great deal of effort to dissecting animals and studying living things. He supposed that they had distinctive special capacities that set them apart from things that aren’t alive. Inspired by the mechanical inventions of his times, the Renaissance philosopher Rene Descartes (1596-1650) believed that living things were like clockwork machines, their special capacities deriving from the way their parts were organized.

In 1944, the physicist Erwin Schrödinger (1887-1961) wrote What is Life? In it, he proposed that the fundamental phenomena of life, including even how parents pass on their traits to their offspring, could be understood by studying the physics and chemistry of living things. Schrödinger’s book was an inspiration to the science of molecular biology.

Living organisms are made of large complicated molecules with backbones of linked carbon atoms. Molecular biologists were able to explain many of the functions of life in terms of these organic molecules and the chemical reactions they undergo when dissolved in liquid water. In 1955 James Watson and Francis Crick discovered the structure of deoxyribonucleic acid (DNA) and showed how it could be the storehouse of hereditary information passed from parent to offspring.

While all this research and theorizing has vastly increased our understanding of life, it hasn’t produced a satisfactory definition of life; a definition that would allow us to reliably distinguish things that are alive from things that aren’t. In 2012 the philosopher Edouard Mahery argued that coming up with a single definition of life was both impossible and pointless. Astrobiologists get by as best they can with definitions that are partial, and that have exceptions. Their search is conditioned by our knowledge of the specific features of life on Earth; the only life we currently know.

Here on Earth, living things are distinctive in their chemical composition. Besides carbon, the elements hydrogen, nitrogen, oxygen, phosphorus, and sulfur are particularly important to the large organic molecules that make up terrestrial life. Water is a necessary solvent. Since we don’t know for sure what else might be possible, the search for extraterrestrial life typically assumes its chemical composition will be similar to that of life on Earth.

Making use of that assumption, astrobiologists assign a high priority to the search for water on other celestial bodies. Spacecraft evidence has proven that Mars once had bodies of liquid water on its surface. Determining the history and extent of this water is a central goal of Mars exploration. Astrobiologists are excited by evidence of subsurface oceans of water on Jupiter’s moon Europa, Saturn’s moon Enceladus, and perhaps on other moons or dwarf planets. But while the presence of liquid water implies conditions appropriate for Earth-like life, it doesn’t prove that such life exists or has ever existed.

Jupiter’s icy moon Europa appears to host liquid water, an essential condition for life as we know it on Earth. Its surface is covered with a crust of water ice. The Voyager and Galileo spacecraft have provided evidence that under this icy crust, there is an ocean of saltwater, containing more liquid water than all the oceans of Earth. Europa’s interior is heated by gravitational tidal forces exerted by giant Jupiter. This heat energy may drive volcanism, hydrothermal vents, and the production of chemical energy sources that living things could make use of. Interaction between materials from Europa’s surface and the ocean environment beneath could make available carbon and other chemical elements essential for Earth-like life.
Credits: NASA/Jet Propulsion Laboratory, SETI Institute

Organic chemicals are necessary for Earth-like life, but, as for water, their presence doesn’t prove that life exists, because organic materials can also be formed by non-biological processes. In 1976, NASA’s two Viking landers were the first spacecraft to make fully successful landings on Mars. They carried an instrument; called the gas chromatograph-mass spectrometer, that tested the soil for organic molecules.

Even without life, scientists expected to find some organic materials in the Martian soil. Organic materials formed by non-biological processes are found in carbonaceous meteorites, and some of these meteorites should have fallen on Mars. They were surprised to find nothing at all. At the time, the failure to find organic molecules was considered a major blow to the possibility of life on Mars.

In 2008, NASA’s Phoenix lander discovered an explanation of why Viking didn’t detect organic molecules. If found that the Martian soil contains perchlorates. Containing oxygen and chlorine, perchlorates are oxidizing agents that can break down organic material. While perchlorates and organic molecules could coexist in Martian soil, scientists determined that heating the soil for the Viking analysis would have caused the perchlorates to destroy any organic material it contained. Martian soil might contain organic materials, after all.

At a news briefing in December 2014, NASA announced that an instrument carried on board the Curiosity Mars rover had succeeded in detected simple organic molecules on Mars for the first time. Researchers believe it is possible that the molecules detected may be breakdown products of more complex organic molecules that were broken down by perchlorates during the process of analysis.

electron micrograph of Mars meteorite — In 1996 a team of scientists lead by Dr. David McKay of NASA’s Johnson Space Center announced possible evidence of life on Mars. The evidence came from their studies of a Martian meteorite found in Antarctica, called Alan Hills 84001. The researchers found chemical and physical traces of possible life including carbonate globules that resemble terrestrial nanobacteria (electron micrograph shown) and polycyclic aromatic hydrocarbons. In terrestrial rock, the chemical traces would be considered breakdown products of bacterial life. The findings became the subject of controversy as non-biological explanations for the findings were found. Today, they are no longer regarded as definitive evidence of Martian life.
Credits: NASA Johnson Space Center

The chemical make-up of terrestrial life has also guided the search for traces of life in Martian meteorites. In 1996 a team of investigators lead by David McKay of the Johnson Space Center in Houston reported evidence that a Martian meteorite found at Alan Hills in Antarctica in 1984 contained chemical and physical evidence of past Martian life.

There have since been similar claims about other Martian meteorites. But, non-biological explanations for many of the findings have been proposed, and the whole subject has remained embroiled in controversy. Meteorites have not so far yielded the kind of evidence needed to prove the existence of extraterrestrial life beyond reasonable doubt.

Following Aristotle, most scientists prefer to define life in terms of its capacities rather than its composition. In the second installment, we will explore how our understanding of life’s capacities has influenced the search for extraterrestrial life.

References and further reading:

N. Atkinson (2009) Perchlorates and Water Make for Potential Habitable Environment on Mars, Universe Today.

S. A. Benner (2010), Defining life, Astrobiology, 10(10):1021-1030.

E. Machery (2012), Why I stopped worrying about the definition of life…and why you should as well, Synthese, 185:145-164.

L. J. Mix (2015), Defending definitions of life, Astrobiology, 15(1) posted on-line in advance of publication.

T. Reyes (2014) NASA’s Curiosity Rover detects Methane, Organics on Mars, Universe Today.

S. Tirard, M. Morange, and A. Lazcano, (2010), The definition of life: A brief history of an elusive scientific endeavor, Astrobiology, 10(10):1003-1009.

Did Viking Mars landers find life’s building blocks? Missing piece inspires new look at puzzle. Science Daily Featured Research Sept. 5, 2010

NASA rover finds active and ancient organic chemistry on Mars, Jet Propulsion laboratory, California Institute of Technology, News, Dec. 16, 2014.

Europa: Ingredients for Life?, National Aeronautics and Space Administration.

December 1, 2014April 26, 2016 by Paul Patton

Communicating Across the Cosmos 4: The Quest for a Rosetta Stone

The Rosetta stone, now displayed at the British Museum in London, was used by Jean-Francois Champollion to decipher Egyptian heiroglyphics, Credit: Hans Hillewaert, British Museum

On television and in the movies, it’s so easy. Aliens almost always speak English (at least in America they do). If it’s explained at all, we are typically told that they learned it by intercepting communications with our astronauts, or tapping into our television broadcasts. A universal translator device instantly abolishes communication difficulties. Hollywood aliens are, of course, human beings in costumes (these days augmented by computer graphics). They are equipped, as are we all, with a human brain, a human larynx, and human vocal cords; all singular products of the distinctive evolutionary history of our species.

Real extraterrestrials, if they exist, will be the product of a different evolutionary history, played out on another world.

They will know no human language, and be unfamiliar with the typical activities of human beings. Here on Earth no archeologist has ever deciphered an ancient script without knowing the language it corresponds to, even though such scripts deal with recognizable human activities. How could we ever devise a message that aliens could understand? Could we ever understand a message they sent to us? Communicating with alien minds may be one of the most daunting challenges the human intellect has ever faced.

In mid-November, the SETI Institute in Mountain View, California sponsored an academic conference on the problem interstellar communication ‘Communicating across the Cosmos’. The conference drew 17 speakers from a variety of disciplines, including linguistics, anthropology, archeology, mathematics, cognitive science, radio astronomy, and art. In this final installment, we will search for clues to a solution to the daunting problem of making ourselves understood to an extraterrestrial civilization.

Conference presenter and archeologist Paul Wason believes that the history of archeology provides an important lesson for how we might devise a message that can be deciphered by extraterrestrials. In the early 19th century the French archeologist Jean-Francois Champollion solved one of the great riddles of his field by deciphering Egyptian hieroglyphics. The critical clue was provided by an artifact discovered in 1799 in an Egyptian town that Europeans called Rosetta. It became known as the Rosetta stone.

The stone contained the same inscription in three different scripts. One of them was Egyptian hieroglyphics, and another was Greek, which Champollion knew how to read. Champollion used the Greek to decipher the hieroglyphics. Could we use the same strategy to create a cosmic Rosetta stone? Like Wason, Carl Sagan also grasped the importance of the Rosetta stone, and discussed it extensively in his 1980’s book and television series Cosmos. To create a cosmic Rosetta stone, we would need a language to stand in the role of Greek. It would need to be known both to us, and to the aliens. Could there possibly be such a thing?

Many mathematicians and physical scientists involved in SETI believe that mathematical and physical concepts could play the needed role. According to mathematician and conference speaker Carl DeVito, the natural numbers (0, 1, 2, 3 …) are useful to humans in dealing with the cyclical processes that are a everywhere in nature, and probably arise universally in the minds of intelligent beings. Astronomers have strong evidence that the laws of physics and chemistry worked out in laboratories here on Earth hold everywhere in the universe. That being the case, they hope that humans and aliens share a common understanding of basic concepts in these fields. If this is so, then such concepts might play the same role that Greek did for Champollion. SETI pioneers Carl Sagan and Frank Drake, along with their collaborators, employed a rudimentary version of this strategy when they constructed the message encoded on the phonographic record launched into space in 1977 aboard the Voyager 1 and 2 spacecraft. These spacecraft hurtled into interstellar space following the completion of their missions to explore the outer solar system.

An image encoded on the phonographic record carried aboard Voyager 1 and 2, intended to communicate how humans symbolize basic mathematical concepts. The left side depicts how humans, in western culture, represent the natural numbers using binary code and Arabic numerals. The vertical lines indicate binary ‘1’, and the horizontal lines binary ‘0’. On the right, additional numerals are given, and the use of scientific notation, and the operations of addition, multiplication, and division are depicted. Credit: Frank Drake

An image encoded on the Voyager record intended to communicate standards of time, mass, and length to an extraterrestrial viewer, using basic concepts in physics encoded symbolically. In the upper right corner, each circle symbolizes a hydrogen atom. The diagram as a whole symbolizes a transition of the spin state of the electron. This transition involves the emission of a microwave radio wave of wavelength 21 centimeters, which is symbolized on the right side of the diagram. Radio emissions produced by this transition occurring in clouds of hydrogen gas in interstellar space are well known to radio astronomers. The wavelength is used as the standard of length (1 L). The time that this transition takes to occur is used as the unit of time (1t) and the mass of a hydrogen atom (1 M) is used as the standard of mass. Various units of measurement used by humans are then defined in terms of these standards. The units are then used throughout the pictorial portion of the message to indicate masses, lengths and times. Credit: Frank Drake

Sagan, Drake, and their collaborators first used symbols in an attempt to communicate how humans represent the natural numbers using binary and base ten numerals. They used another set of symbols to depict some properties of the hydrogen atom, which they used to establish standards of distance and time. The distance and time standards were used repeatedly throughout the digital image portion of the message to specify the sizes and time scales depicted. The Voyager record included a greeting from then President Carter encoded as English text. Sagan, Drake, and their collaborators didn’t even attempt the monumental, and perhaps impossible, task of explaining President Carter’s text statement using their Rosetta stone.

Much like Wason and Sagan, computer scientist and conference presenter Kim Binsted, felt that the solution to interstellar communication lies in constructing a pidgin, a simplified version of a language developed to communicate between groups that share no language in common. She was doubtful though, that a cosmic Rosetta stone based on physics and math would let humans and aliens communicate about anything other than physics and math. It might never, for example, provide a way to convey the President’s good wishes. The hieroglyphics of the Rosetta stone were decipherable, in part, because they described the familiar human activities of an Egyptian pharaoh. Humans are clueless about what sorts of activities aliens typically engage in, and aliens are equally clueless about us. It’s hard to see how a Rosetta stone based on physics could bridge this sort of gap.

Philosophers Nicholas Rescher and Andre Kukla, neither of whom presented at the conference, have raised a more fundamental objection. They question whether extraterrestrials would use the same concepts to understand the physical and chemical world that we do. The concepts that modern western science uses to understand the physical world surely reflect the structure of that world. But they also reflect the history of our culture and the structure of our minds. Since aliens would differ from humans on both counts, it’s at least possible that their physical, and even their mathematical concepts might be different from ours. If that’s so, then physics can’t play the role that Greek did for Champollion. Every path forward is full of unknowns and difficulties, and Kim Binsted doubts a solution is possible.

There is a glimmering of hope for another kind of Rosetta stone based on another sort of “Greek”. Given the central role that visual images played in the Voyager message, it’s surprising that image based communication strategies didn’t receive greater emphasis at the conference. It’s true that here on Earth; animals have evolved a wide variety of non-visual ways to sense their surroundings. Some fishes can sense their environments by generating and detecting electric fields in the water. Many fish can use fields of water flow around their bodies to detect nearby objects. Bats, along with dolphins and whales, have evolved a sonar system, emitting sounds and analyzing their returning echoes. Scorpions can sense ground vibrations, elephants can hear sounds below the range of human hearing, and dogs have a remarkably acute sense of smell, to name just a few examples. Still, almost every Earthly animal has eyes of some sort.

Earthly evolution has invented vision several times, in different animal lineages. Vision is especially important for larger animals that live on land. This is because larger bodies can make larger eyes and larger eyes can give sharper vision and better light gathering abilities. Land environments are typically better lit than aquatic ones. Birds and mammals are the Earthly animals with the biggest and most sophisticated brains, and they also have the most acute vision.

Are alien environments likely to be well lit? Exoplanet hunters have focused their efforts on finding planets like the Earth, rocky terrestrial planets at the right distance from their star for temperatures to be in the range where water is a liquid. They have shown us that such worlds are fairly commonplace in the cosmos. The daytime surfaces of these exoplanets are likely to be flooded with visible light, just as is Earth. This light may be necessary for life on such a world, because most life on Earth depends on the energy of sunlight as trapped by green plants. For large, land dwelling animals in this kind of environment, vision provides more information, at a distance, than any other sense can. Since it evolved numerous times on Earth, it’s likely to do so elsewhere as well.

The eye of a squid is remarkably similar to our own. Squids are part of a group of animals called molluscs, which also includes slugs, snails, and shellfish. Molluscs are very distantly related to the vertebrates (animals with backbones, a group which includes humans). The most recent common ancestor of molluscs and vertebrates was a simple wormlike creature that lived more than 600 million years ago. The two groups have followed an independent course of evolution ever since. The fact that molluscs evolved complex brains and bodies along a different evolutionary path than vertebrates makes them a good model for understanding extraterrestrials. One group of molluscs, the cephalopods, a group which includes squids, octopuses, and cuttlefish, have evolved the largest and most complex brains of any invertebrate. Despite their separate evolutionary origin, the eyes of cephalopods are remarkably similar to vertebrate eyes, a phenomenon known as convergent evolution. Evolution solved similar problems in similar ways. These similarities suggest the possible usefulness of images in interstellar messages. — With a lens at the front and a sheet of light sensing cells at the back, the eye of a squid is remarkably similar to our own. Squids are part of a group of animals called molluscs, which also includes slugs, snails, and shellfish. Molluscs are very distantly related to the vertebrates (animals with backbones, a group which includes humans). The most recent common ancestor of molluscs and vertebrates was a simple worm-like creature that lived more than 600 million years ago. The two groups have followed an independent course of evolution ever since. The fact that molluscs evolved complex brains and bodies along a different evolutionary path than vertebrates makes them a good model for understanding some of the ways in which extraterrestrials, with an entirely separate evolutionary history, might be different from or similar to us. One group of molluscs, the cephalopods, a group which includes squids, octopuses, and cuttlefish, have evolved the largest and most complex brains of any invertebrates. Despite their separate evolutionary origin, the eyes of cephalopods are remarkably similar to vertebrate eyes, a phenomenon known as convergent evolution. Evolution solved similar problems in similar ways. Perhaps, even on another planet, evolution solves similar problems in similar ways. If aliens, like cephalopods, have some visual similarities to us, then visual images may be useful in interstellar messages. Credit: Carl Chun Die Cephaloden

The human visual system gathers information about a three dimensional world of objects and surfaces, partly by using motion cues. We have the ability to represent that world in two dimensions, using images. Kim Binsted worried that an alien visual system might not be capable of making sense of pictures made by humans. This worry was a potent one for the stick figures and line drawings that played such a prominent role in the pioneering interstellar messages of the 70’s. Those kinds of depictions use abstract visual conventions that an alien viewer might find impossible to figure out. Today, though, we needn’t worry about stick figures, because the information revolution gives us the ability to send high definition video. Still, we can’t be sure what an alien visual system would make of imagery encoded with the human visual system in mind.

Video imagery may provide a promising complement or alternative to the abstractions of physics and chemistry as the “Greek” for a cosmic Rosetta stone. If the aliens live on a planet like Earth, with liquid water on its surface, then we will share a mutual familiarity with water’s many manifestations. Just like us, aliens will have seen rain and snow, oceans, rivers, lakes, ponds, clouds, fog, and rainbows. If they have a sense of hearing, over a range of sound frequencies at least somewhat similar to ours, they will have heard waves crashing on beaches, rain hitting the ground, gurgling brooks, and the splash of a pebble dropped into a pond. When the senses work together to confirm one another, the certainty of perceptual recognition is even greater.

An audio-video movie depicting the mutually familiar phenomena of water could be just the bridge we need to cross the gulf of mutual incomprehension. This splashy, gurgling “Greek” could be the key to helping the aliens understand our audio-visual and still images, and ultimately, our symbols. As with the Voyager record, a simpler symbol system would first be needed to communicate to the aliens about how to view and listen to the presentation. That might be a big stumbling block. In the case of Voyager, a stylus head for playing the record was included on the spacecraft, which made it simpler to explain how to play it. A Rosetta stone that led the extraterrestrials to an understanding of our images could provide a means of communication extending well beyond the topics of physics, chemistry, and math. Several conference participants felt that imagery might help to convey things about human altruism, cooperation, morality, and aesthetic sensibilities.

The main message of the ‘Communicating across the Cosmos’ conference is a recognition of just how hard the problem of making ourselves understood to aliens will be. Kim Binsted ended her talk on a faint note of optimism. Even if all else fails, she supposed, there is something we can still communicate to the aliens. She showed a slide of her home doorbell. When it rings, she said, it conveys the message that someone is there, and where they are. It shows intent to communicate, and a benign willingness to reveal one’s presence. Even if it can’t be interpreted, an interstellar message conveys the information that a doorbell conveys. That message, the message that someone is there, would still be of monumental importance.

Even an interstellar message that can't be deciphered still tells us what a doorbell tells us: that someone is there. — Even an interstellar message that can’t be deciphered still tells us what a doorbell tells us: that someone is there. Credit: Jim Kuhn

Previous articles in this series:
Part 1: Shouting into the Darkness
Part 2: Petabytes from the Stars
Part 3: Bridging the Vast Gulf

References and Further Reading:

Communicating across the Cosmos: How can we make ourselves understood by other civilizations in the galaxy (2014), SETI Institute Conference Website.

F. Cain (2013) How Could We Find Aliens? The Search for Extraterrestrial Intelligence (SETI), Universe Today.

F. Cain (2013) Where Are All The Aliens? The Fermi Paradox, Universe Today.

A. Kukla (2010) Extraterrestrials: A Philosophical Perspective, Rowman and Littlefield Publishers Inc. Plymouth, UK.

M. F. Land and D-E. Nilsson (2002), Animal Eyes, Oxford University Press.

N. Rescher (1985) Extraterrestrial Science, in Extraterrestrials: Science and Alien Intelligence, Edited by E. Regis, Cambridge University Press, Cambridge, UK.

C. Sagan, F. D. Drake, A. Druyan, T. Ferris, J. Lomberg, L. S. Sagan, (1978) Murmurs of Earth: The Voyager Interstellar Record. Random House, New York.

C. Sagan (1980) Cosmos, Random House, New York.

J. J. Vitti (2013) Cephalopod cognition in an evolutionary context: Implications for ethology, Biosemiotics, 6:393-401.

November 20, 2014December 23, 2015 by Paul Patton

Communicating Across the Cosmos, Part 1: Shouting into the Darkness

The 70 meter Evpatoria Planetary Radar radio telescope in the Crimea was used to transmit 4 interstellar messages in 1999, 2001, 2003, and 2008

Over the last 20 years, astronomers have discovered several thousand planets orbiting other stars. We now know that potentially habitable Earth-like planets are abundant in the cosmos. Such findings lend a new plausibility to the idea that intelligent life might exist on other worlds. Suppose that SETI (Search for Extraterrestrial Intelligence) researchers succeed in their quest to find a message from a distant exoplanet. How much information can we hope to receive or send? Can we hope to decipher its meaning? Can humans compose interstellar messages that are comprehensible to alien minds?

Such concerns were the topic of a two day academic conference on interstellar messages held at the SETI Institute in Mountain View, California; ‘Communicating across the Cosmos’. The conference drew 17 speakers from a wide variety of disciplines, including linguistics, anthropology, archeology, mathematics, cognitive science, philosophy, radio astronomy, and art. This article is the first of a series of installments about the conference. Today, we’ll explore the ways in which our society is already sending messages to extraterrestrial civilizations, both accidentally and on purpose.

Sending radio messages over sizable interstellar distances is feasible with present day technology. According to SETI Institute radio astronomer Seth Shostak, who presented at the conference, we are already — by accident — constantly signaling our presence to any extraterrestrial astronomers that might exist in our neighborhood of the galaxy. Some radio signals intended for domestic uses leak into space. The most powerful come from radars used for military purposes, air traffic control, and weather forecasting. Because these radars sweep across broad swaths of the sky, their signals travel out into space in many directions.

With radio telescopes no more sensitive than those astronomers on Earth use today, extraterrestrials out to distances of tens of light years could detect them and figure out that they were artificial. The Arecibo radar telescope in Puerto Rico is designed specifically to send a narrow beam of radio waves into space, usually to bounce them off celestial bodies and learn about their surfaces. For a receiver within its beam, it could be detected hundreds of light-years away.

FM radio and television broadcasts also leak out into space, but they are weaker and couldn’t be detected more than about one tenth of a light year away with present day human technology. This is quite a bit less than the distance to the nearest star. The size and sensitivity of radio telescopes is progressing rapidly. An alien civilization just a few centuries more advanced than us in radio technology could detect even these weak signals over vast distances in the galaxy. As our signals spread outward at the speed of light, they will reach progressively larger numbers of stars and planets, any one of which might be home to ETI. If they really are out there, they are likely to find us eventually.

Humans have been fascinated with formulating messages for extraterrestrials for a surprisingly long time. Eighteenth and nineteenth century scientists drew up proposals to make huge fire pits or plantings in the shapes of geometric figures that they hoped would be visible in the telescopes of the inhabitants of neighboring worlds. In the early days of radio, attempts were made to contact Mars and Venus.

As prospects for intelligent life within the solar system dimmed, attention turned to the stars. In the early 1970’s the first two spacecraft to escape the sun’s gravitational pull, Pioneer 10 and 11, each carried an engraved plaque designed to tell aliens where Earth is, and what human beings look like. Voyager 1 and 2 carried a more ambitious message of images and sounds encoded on a phonograph record. Both the Pioneer plaques and the Voyager records were devised by teams led by astronomers Carl Sagan and Frank Drake, both SETI pioneers. In 1974, the powerful Arecibo radio telescope beamed a brief 3 minute message towards a star cluster 21,000 light years away as part of a dedication ceremony for a major upgrade. The binary coded message was an image, including a stick figure of a human, our solar system, and some chemicals important to earthly life. The distant target was chosen simply because it was overhead at the time of the ceremony.

The plaque affixed to the Pioneer 10 and 11 spacecraft, the first spacecraft to leave our solar system. In the upper left corner is a diagram depicting the hydrogen atom, the most abundant element in the universe. The diagram symbolizes the transition of the electron from a spin-up to a spin-down state. This transition is responsible for radio emissions at the wavelength of 21 cm by clouds of hydrogen in interstellar space. This phenomenon is familiar to radio astronomers and provides a distance standard for indicating the size of the humans. In the middle left is a representation of position of the sun with respect to the center of the galaxy and 14 pulsars. At the bottom is a map of the solar system indicating the origin of the spacecraft at the sun's third planet. The planets relative distances from the sun are given as binary numbers with the unit being one tenth of Mercury's distance from the sun. At the right is a depiction of a human couple with the man's arm raised in gesture of friendly greeting and the pioneer spacecraft drawn in outline as a backdrop. — The plaque affixed to the Pioneer 10 and 11 spacecraft, the first spacecraft to leave our solar system. In the upper left corner is a diagram depicting the hydrogen atom, the most abundant element in the universe. The diagram symbolizes the transition of the electron from a spin-up to a spin-down state. This transition is responsible for radio emissions at the wavelength of 21 cm by clouds of hydrogen gas in interstellar space. This phenomenon is very familiar to radio astronomers and provides a distance standard used to indicate the sizes of the human beings. In the middle left is a representation of position of the sun with respect to the center of the galaxy and 14 pulsars. At the bottom is a map of the solar system indicating the origin of the spacecraft as the sun’s third planet. The relative distances of the planets from the sun are indicated as binary numbers with a unit one tenth the distance of Mercury from the sun. At the right is a depiction of a human couple with the man’s arm raised in a gesture of friendly greeting and the pioneer spacecraft drawn in outline as a backdrop NASA Ames Research Center.

Cultural anthropologist and conference speaker Klara Anna Capova said that in recent years, messaging to extraterrestrials has moved beyond science and become a commercial enterprise. In 1999 and 2003, a private company solicited content from the general public and transmitted these ‘Cosmic Call’ messages to several nearby sun-like stars from the 70 meter radio telescope of the Evpatoria Deep Space Center in Crimea, Ukraine.

In 2009, another private company transmitted 25,000 messages, collected via a website, towards the red dwarf star Gliese 581, 20 light years away. In 2008, a Dorito’s commercial was beamed to a sun-like star 42 light years away, and in 2009 Penguin books transmitted 1000 messages as part of a book promotion. In 2010, a greeting, spoken in the fictional Klingon language, was beamed towards the star Arcturus, 37 light years away. The message was sent to promote the opening of what was billed as the first authentic Klingon opera on Earth. As one conference speaker noted, there are no regulations on the transmission or content of such messages.

Actively messaging extraterrestrials is a controversial practice, and the director of the Evpatoria Center, Alexander Zaitsev, has faced criticism from some members of the scientific community for his actions. Traditionally, SETI researchers have simply listened for alien messages. A received message might allow humans to learn something about the nature and motives of its extraterrestrial senders. That might give us a basis for deciding whether or not it was wise and prudent to reply.

Drake’s Arecibo message, by intent, was beamed at a star cluster tens of thousands of light years away and was meant simply to demonstrate the capacity for interstellar messaging. The Pioneer and Voyager spacecraft likewise will not reach the stars for tens of thousands of years. On the other hand, the recent transmissions were directed at nearby stars, from which we might receive a reply in less than a century. At the conference, Seth Shostak advanced what he confessed was a provocative position. He said we shouldn’t worry too much about the recent transmissions, because the much weaker signals that constantly emanate from Earth would be detectable by extraterrestrial civilizations with more advanced radio technology anyway. “That horse”, he said “has already left the barn”.

In the next installment, we will explore the SETI Institute’s current and planned efforts to conduct our human search for extraterrestrial signals. We will consider the limits of our own signaling capacity, and learn that the amount of information we could send the aliens is truly vast.

References and Further Reading:

Communicating across the Cosmos: How can we make ourselves understood by other civilizations in the galaxy (2014), SETI Institute Conference Website

N. Atkinson (2008), Message from Earth beamed to alien world, Universe Today.

F. Cain (2013), How could we find aliens? The search for extraterrestrial intelligence (SETI), Universe Today.

M. J. Crowe (1986) The Extraterrestrial Life Debate 1750-1900: The Idea of a Plurality of Worlds From Kant to Lowell, University of Cambridge, Cambridge, UK.

C. Sagan, F. Drake, A. Druyan, T. Ferris, J. Lomberg, L. S. Sagan (1978), Murmurs of Earth: The Voyager Interstellar Record, Random House, New York, NY.

W. T. Sullivan III; S. Brown, and C. Wetherill, (1978) Eavesdropping: The radio signature of Earth, Science 199(4327): 377-388.