An artists depiction of how the spectra of elements in the stars of the Milky Way reflect the importance these elements play in human life. Credit: Dana Berry/SkyWorks Digital Inc.; SDSS collaboration.
Scientist Carl Sagan said many times that “we are star stuff,” from the nitrogen in our DNA, the calcium in our teeth, and the iron in our blood.
It is well known that most of the essential elements of life are truly made in the stars. Called the “CHNOPS elements” – carbon, hydrogen, nitrogen, oxygen, phosphorous, and sulfur – these are the building blocks of all life on Earth. Astronomers have now measured of all of the CHNOPS elements in 150,000 stars across the Milky Way, the first time such a large number of stars have been analyzed for these elements.
“For the first time, we can now study the distribution of elements across our Galaxy,” says Sten Hasselquist of New Mexico State University. “The elements we measure include the atoms that make up 97% of the mass of the human body.”
Astronomers with the Sloan Digital Sky Survey made their observations with the APOGEE (Apache Point Observatory Galactic Evolution Experiment) spectrograph on the 2.5m Sloan Foundation Telescope at Apache Point Observatory in New Mexico. This instrument looks in the near-infrared to reveal signatures of different elements in the atmospheres of stars.
Quote from Carl Sage. Credit: Pinterest
While the observations were used to create a new catalog that is helping astronomers gain a new understanding of the history and structure of our galaxy, the findings also “demonstrates a clear human connection to the skies,” said the team.
While humans are 65% oxygen by mass, oxygen makes up less than 1% of the mass of all of elements in space. Stars are mostly hydrogen, but small amounts of heavier elements such as oxygen can be detected in the spectra of stars. With these new results, APOGEE has found more of these heavier elements in the inner part of the galaxy. Stars in the inner galaxy are also older, so this means more of the elements of life were synthesized earlier in the inner parts of the galaxy than in the outer parts.
So what does that mean for those of us out on the outer edges of one of the Milky Way’s spiral arms, about 25,000 light-years from the center of the galaxy?
“I think it’s hard to say what the specific implications are for when life could arise,” said team member Jon Holtzman, also from New Mexico State, in an email to Universe Today. “We measure typical abundance of CHNOPS elements at different locations, but it’s not so easy to determine at any given location the time history of the CHNOPS abundances, because it’s hard to measure ages of stars. On top of that, we don’t know what the minimum amount of CHNOPS would need to be for life to arise, especially since we don’t really know how that happens in any detail!”
Holtzman added it is likely that, if there is a minimum required abundance, that minimum was probably reached earlier in the inner parts of the Galaxy than where we are.
The team also said that while it’s fun to speculate how the composition of the inner Milky Way Galaxy might impact how life might arise, the SDSS scientists are much better at understanding the formation of stars in our Galaxy.
“These data will be useful to make progress on understanding Galactic evolution,” said team member Jon Bird of Vanderbilt University, “as more and more detailed simulations of the formation of our galaxy are being made, requiring more complex data for comparison.”
Sloan Foundation 2.5m Telescope at Apache Point Observatory. Credit: SDSS.
“It’s a great human interest story that we are now able to map the abundance of all of the major elements found in the human body across hundreds of thousands of stars in our Milky Way,” said Jennifer Johnson of The Ohio State University. “This allows us to place constraints on when and where in our galaxy life had the required elements to evolve, a sort ‘temporal Galactic habitable zone’”.
The catalog is available at the SDSS website, so take a look for yourself at the chemical abundances in our portion of the galaxy.
NASA’s OSIRIS-REx asteroid sampling spacecraft, return capsule and payload fairings inside the Payloads Hazardous Servicing Facility high bay at NASA's Kennedy Space Center is being processed for Sep. 8, 2016 launch to asteroid Bennu from Cape Canaveral, FL. Credit: Ken Kremer/kenkremer.com
NASA’s OSIRIS-REx asteroid sampling spacecraft, return capsule and payload fairings inside the Payloads Hazardous Servicing Facility high bay at NASA’s Kennedy Space Center is being processed for Sep. 8, 2016 launch to asteroid Bennu from Cape Canaveral, FL. Credit: Ken Kremer/kenkremer.com
KENNEDY SPACE CENTER, FL – OSIRIS-Rex, the first American sponsored probe aimed at retrieving “pristine materials” from the surface of an asteroid and returning them to Earth has been fully assembled at its Florida launch base and is ready to blastoff ten days from today on Sep. 8. It’s a groundbreaking mission that could inform us about astrobiology and the ‘Origin of Life.’
“We are interested in that material because it is a time capsule from the earliest stages of solar system formation,” said Dante Lauretta, principal investigator for OSIRIS-REx at the University of Arizona, Tucson, in an interview with Universe Today beside the completed spacecraft inside the Payloads Hazardous Servicing Facility, or PHSF, clean room processing facility at NASA’s Kennedy Space Center in Florida.
With virtually all prelaunch processing complete, leading members of the science, engineering and launch team including Lauretta met with several members of the media, including Universe Today, inside the clean room for a last and exclusive up-close look and briefing with the one-of-its-kind $800 million Asteroid sampling probe last week.
OSIRIS-REx goal is to fly on a roundtrip seven-year journey to the near-Earth asteroid target named Bennu and back. 101955 Bennu is a near Earth asteroid and was selected specifically because it is a carbon-rich asteroid.
While orbiting Bennu it will move in close and snatch pristine soil samples containing organic materials from the surface using the TAGSAM collection dish, and bring them back to Earth for study by researchers using all of the most sophisticated science instruments available to humankind.
“The primary objective of the OSIRIS-Rex mission is to bring back pristine material from the surface of the carbonaceous asteroid Bennu, OSIRIS-Rex Principal Investigator Dante Lauretta told Universe Today in the PHSF, as the probe was undergoing final preparation for shipment to the launch pad.
“It records the very first material that formed from the earliest stages of solar system formation. And we are really interested in the evolution of carbon during that phase. Particularly the key prebiotic molecules like amino acids, nucleic acids, phosphates and sugars that build up. These are basically the biomolecules for all of life.”
Overhead view of NASA’s OSIRIS-REx asteroid sampling spacecraft with small white colored sample return canister atop, inside the Payloads Hazardous Servicing Facility high bay at NASA’s Kennedy Space Center. Launch is slated for Sep. 8, 2016 to asteroid Bennu from Cape Canaveral Air Force Station, FL. Credit: Julian Leek
OSIRIS-REx will gather rocks and soil and bring at least a 60-gram (2.1-ounce) sample back to Earth in 2023. It has the capacity to scoop up to about 1 kg or more.
The mission will help scientists investigate how planets formed and how life began. It will also improve our understanding of asteroids that could impact Earth by measuring the Yarkovsky effect.
I asked Lauretta to explain in more detail why was Bennu selected as the target to answer fundamental questions related to the origin of life?
“We selected asteroid Bennu as the target for this mission because we feel it has the best chance of containing those pristine organic compounds from the early stage of solar system formation,” Lauretta told me.
“And that information is based on our ground based spectral characterization using telescopes here on Earth. Also, space based assets like the Hubble Space Telescope and the Spitzer Space Telescope.”
What is known about the presence of nitrogen containing compounds like amino acids and other elements on Bennu that are the building blocks of life?
“When we look at the compounds that make up these organic materials in these primitive asteroidal materials, we see a lot of carbon,” Lauretta explained.
“But we also see nitrogen, oxygen, hydrogen, sulfur and phosphorous. We call those the CHONPS. Those are the six elements we really focus on when we look at astrobiology and prebiotic chemistry and how those got into the origin of life.”
View of science instrument suite and TAGSAM robotic sample return arm on NASA’s OSIRIS-REx asteroid sampling spacecraft inside the Payloads Hazardous Servicing Facility at NASA’s Kennedy Space Center. Probe is slated for Sep. 8, 2016 launch to asteroid Bennu from Cape Canaveral Air Force Station, FL. Credit: Ken Kremer/kenkremer.com
The OSIRIS-REx spacecraft was built for NASA by prime contractor Lockheed Martin at their facility near Denver, Colorado and flown to the Kennedy Space Center on May 20.
For the past three months it has undergone final integration, processing and testing inside the PHSF under extremely strict contamination control protocols to prevent contamination by particle, aerosols and most importantly organic residues like amino acids that could confuse researchers seeking to discover those very materials in the regolith samples gathered for return to Earth.
The PHFS clean room was most recently used to process the Orbital ATK Cygnus space station resupply vehicles. It has also processed NASA interplanetary probes such as the Curiosity Mars Science Laboratory and MAVEN Mars orbiter missions.
Side view of NASA’s OSIRIS-REx asteroid sampling spacecraft showing the High Gain Antenna at left and solar panel, inside the Payloads Hazardous Servicing Facility high bay at NASA’s Kennedy Space Center. Probe is being processed for Sep. 8, 2016 launch to asteroid Bennu from Cape Canaveral Air Force Station, FL. Credit: Ken Kremer/kenkremer.com
The spacecraft will reach Bennu in 2018. Once within three miles (5 km) of the asteroid, the spacecraft will begin at least six months of comprehensive surface mapping of the carbonaceous asteroid, according to Heather Enos, deputy principal investigator, in an interview with Universe Today.
“We will then move the spacecraft to within about a half kilometer or so to collect further data,” Enos elaborated.
It will map the chemistry and mineralogy of the primitive carbonaceous asteroid. The team will initially select about 10 target areas for further scrutiny as the sampling target. This will be whittled down to two, a primary and backup, Enos told me.
After analyzing the data returned, the science team then will select a site where the spacecraft’s robotic sampling arm will grab a sample of regolith and rocks. The regolith may record the earliest history of our solar system.
Engineers will command the spacecraft to gradually move on closer to the chosen sample site, and then extend the arm to snatch the pristine samples the TAGSAM sample return arm.
PI Lauretta will make the final decision on when and which site to grab the sample from.
“As the Principal Investigator for the mission I have responsibility for all of the key decisions during our operations,” Lauretta replied. “So we will be deciding on where we want to target our high resolution investigations for sample site evaluation. And ultimately what is the one location we want to send the spacecraft down to the surface of the asteroid to and collect that sample.”
“And then we have to decide like if we collected enough sample and are we ready to stow it in the sample return capsule. Or are we going to use one of our 2 contingency bottles of gas to go for a second attempt.”
“The primary objective is one successful sampling event. So when we collect 60 grams or 2 ounces of sample then we are done!”
“In the event that we decide to collect more, it will be intermixed with anything we collected on the first attempt.”
The priceless sample will then be stowed in the on board sample return capsule for the long journey back to Earth.
NASA’s OSIRIS-Rex asteroid sampling spacecraft inside the Payloads Hazardous Servicing Facility high bay at NASA’s Kennedy Space Center. Launch is slated for Sep. 8, 2016 to asteroid Bennu from Cape Canaveral Air Force Station, FL. Credit: Lane Hermann
Bennu is an unchanged remnant from the collapse of the solar nebula and birth of our solar system some 4.5 billion years ago, little altered over time.
Bennu is a near-Earth asteroid and was selected for the sample return mission because it could hold clues to the origin of the solar system and host organic molecules that may have seeded life on Earth.
Artist’s conception of NASA’s OSIRIS-REx spacecraft at Bennu. Credits: NASA/GSFC
OSIRIS-REx will return the largest sample from space since the American and Soviet Union’s moon landing missions of the 1970s.
Watch this USLaunchReport video shot during media visit inside the PHSF on Aug. 20, 2016:
Video caption: Our first introduction to the OSIRIS-REx asteroid bound mission in search of the origins of life, from inside the Payloads Hazardous Servicing Facility at NASA’s Kennedy Space Center on Aug. 20, 2016. Credit: USLaunchReport
OSIRIS-REx is the third mission in NASA’s New Frontiers Program, following New Horizons to Pluto and Juno to Jupiter, which also launched on Atlas V rockets.
NASA’s Goddard Space Flight Center in Greenbelt, Maryland, is responsible for overall mission management.
OSIRIS-REx complements NASA’s Asteroid Initiative – including the Asteroid Redirect Mission (ARM) which is a robotic spacecraft mission aimed at capturing a surface boulder from a different near-Earth asteroid and moving it into a stable lunar orbit for eventual up close sample collection by astronauts launched in NASA’s new Orion spacecraft. Orion will launch atop NASA’s new SLS heavy lift booster concurrently under development.
Watch for Ken’s continuing OSIRIS-REx mission and launch reporting from on site at the Kennedy Space Center and Cape Canaveral Ait Force Station, FL.
Stay tuned here for Ken’s continuing Earth and planetary science and human spaceflight news.
Dr Dante Lauretta, principal investigator for OSIRIS-REx at the University of Arizona, Tucson, and Dr. Ken Kremer, Universe Today point to NASA’s OSIRIS-Rex asteroid sampling spacecraft inside the Payloads Hazardous Servicing Facility at the Kennedy Space Center on Aug. 20, 2016. Credit: Ken Kremer/kenkremer.comThe University of Arizona’s camera suite, OCAMS, sits on a test bench that mimics its arrangement on the OSIRIS-REx spacecraft. The three cameras that compose the instrument – MapCam (left), PolyCam and SamCam – are the eyes of NASA’s OSIRIS-REx mission. They will map the asteroid Bennu, help choose a sample site, and ensure that the sample is correctly stowed on the spacecraft. Credits: University of Arizona/Symeon Platts
Special Guest:
NASA Astrobiologist Dr. Chris McKay organized an August 2014 workshop to discuss the future of a permanent moon base, and the ultimate goal of establishing a human settlement on Mars. The resultant nine papers have been recently published in a special issue of the journal New Space.
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The logo of the METI International Puerto Rico workshop. At the center is Charles Darwin, the nineteenth century British naturalist whose theory of evolution is central to assessing the likelihood and nature of extraterrestrial intelligence. To the left is the octopus, a creature that evolved sophisticated cognition and perception along an evolutionary path quite different from that of humans. To the right is the peacock, whose elaborate tail feathers evolved by sexual selection, a process that may also have been of central importance to the evolution of human intelligence. METI International, used with permisson.
In our galaxy, there may be, at least, tens of billions of habitable planets, with conditions suitable for liquid water on their surfaces. There may be habitable moons as well. On an unknown number of those worlds, life may have arisen. On an unknown fraction of life-bearing worlds, life may have evolved into complex multicellular, sexually reproducing forms.
The purposes of the newly created METI (Messaging to ExtraTerrestrial Intelligence) International include fostering multidisciplinary research in the design and transmission of interstellar messages, and building a global community of scholars from the natural sciences, social sciences, humanities, and arts concerned with the origin, distribution, and future of life in the universe.
On May 18 the organization sponsored a workshop which included presentations by biologists, psychologists, cognitive scientists, and linguists. This is the third and final installment of a series of articles about the workshop.
In previous installments, we’ve discussed some ideas about the evolution of intelligence that were featured at the workshop. Here we’ll see whether our Earthly experience can provide us with any clues about how we might communicate with aliens.
Many of the animals that we are most familiar with from daily life, like humans, cats, dogs, birds, fishes, and frogs are vertebrates, or animals with backbones. They are all descended from a common ancestor and share a nervous system organized according to the same basic plan.
Molluscs are another major group of animals that have been evolving separately from vertebrates for more than 600 million years. Although most molluscs, like slugs, snails, and shellfish, have fairly simple nervous systems, one group; the cephalopods, have evolved a much more sophisticated one. The common octopus, Octopus vulgaris, Is a cephalopod mollusc, has evolved sophisticated cognition and perception along a very different evolutionary path than have human beings and our relatives. The brain is located between the eyes. The large bulbous structure below the eyes is the mantle, a muscular organ involved in swimming. Public domain.
Cephalopods include octopuses, squids, and cuttlefishes. They show cognitive and perceptual abilities rivaling those of our close vertebrate kin. Since this nervous system has a different evolutionary history than of the vertebrates, it is organized in a way completely different from our own. It can give us a glimpse of the similarities and differences we might expect between aliens and ourselves.
David Gire, an associate professor of psychology at the University of Washington, and researcher Dominic Sivitilli gave a presentation on cephalopods at the Puerto Rico workshop. Although these animals have a sophisticated brain, their nervous systems are much more decentralized than that of familiar animals. In the octopus, sensing and moving are controlled locally in the arms, which together contain as many nerve cells, or neurons, as the brain. Dr. David Gire is an Assistant Professor in the Department of Psychology at the University of Washington and a behavioral neuroscientist. He presented at the Puerto Rico workshop on cephalopod intelligence.
The animal’s eight arms are extraordinarily sensitive. Each containing hundreds of suckers, with thousands of sensory receptors on each one. By comparison, the human finger has only 241 sensory receptors per square centimeter. Many of these receptors sense chemicals, corresponding roughly to our senses of taste and smell. Much of this sensory information is processed locally in the arms. When an arm is severed from an octopus’s body, it continues to show simple behaviors on its own, and can even avoid threats. The octopus’s brain simply acts to coordinate the behaviors of its arms.
Cephalopods have acute vision. Although their eyes evolved separately from those of vertebrates, they nonetheless bear an eerie resemblance. They have a unique ability to change the pattern and color of their skin using pigment cells that are under direct control of their nervous systems. This provides them with the most sophisticated camouflage system of any animal on Earth, and is also used for social signaling.
Despite the sophisticated cognitive abilities it exhibits in the lab, the octopus is largely solitary.
Cephalopod groups exchange useful information by observing one another, but otherwise exhibit only limited social cooperation. Many current theories of the evolution of sophisticated intelligence, like Miller’s sapiosexual hypothesis, which was featured in the second installment, assume that social cooperation and competition play a central role in the evolution of complicated brains. Since cephalopods have evolved much more impressive cognitive abilities than other molluscs, their limited social behavior is surprising.
Dominic Sivitilli is a post-baccalaureate researcher in the laboratory of David Gire, studying responses to chemical signals by the octopus. He is the co-presenter of a talk on cephalopod cogntition at the METI International Puerto Rico conference. METI International used with permission.
Maybe the limited social behavior of cephalopods really does set limits on their intelligence. However, Gire and Sivitilli speculate that perhaps “an intelligence capable of technological development could exist with minimum social acuity”, and the cephalopod ability to socially share information is enough. The individuals of such an alien collective, they suppose, might possess no sense of self or other.
Besides Gire and Sivitilli, Anna Dornhaus, whose ideas were featured in the first installment, also thinks that alien creatures might function together as a collective mind. Social insects, in some respects, actually do. She doubts, though, that such an entities could evolve human-like technological intelligence without something like Miller’s sapiosexuality to trigger a runaway explosion of intelligence.
But if non-sapiosexual alien technological civilizations do exist, we might find them impossible to comprehend. Given this possible gulf of incomprehension about social structure, Gire and Stivitilli suppose that the most we might aspire to accomplish in terms of interstellar communication is an exchange of mutually useful and comprehensible astronomical information.
Workshop presenter Alfred Kracher, a retired staff scientist at the Ames Laboratory of the University of Iowa, supposes that “the mental giants of the Milky Way are probably artificially intelligent machines… It would be interesting to find evidence of them, if they exist”, he writes, “but then what?” Kracher supposes that if they have emancipated themselves and evolved away from their makers, “they will have nothing in common with organic life forms, human or extraterrestrial. There is no chance of mutual understanding”. We will be able to understand aliens, he maintains, only if “it turns out that the evolution of extraterrestrial life forms is highly convergent with our own”.
Peter Todd, a professor of psychology from Indiana University, holds out hope that such convergence may actually occur. Earthly animals must solve a variety of basic problems that are presented by the physical and biological world that they inhabit.
They must effectively navigate through a world of surfaces, barriers and objects, finding food and shelter, and avoiding predators, parasites, toxins. Extraterrestrial organisms, if they evolve in an Earth-like environment, would face a generally similar set of problems. They may well arrive at similar solutions, just as the octopus evolved eyes similar to ours.
In evolution here on Earth, Todd notes, brain systems originally evolved to solve these basic physical and biological problems appear to have been re-purposed to solve new and more difficult problems, as some animals evolved to solve the problems of living and finding mates as members of societies, and then as one particular ape species went on to evolve conceptual reasoning and language. For example, disgust at bad food, useful for avoiding disease, may have been become the foundation for sexual disgust to avoid bad mates, moral disgust to avoid bad clan mates, and intellectual disgust to avoid dubious ideas.
If alien brains evolved solutions similar to the ones our brains did for negotiating the physical and biological world, they they might also have been re-purposed in similar ways. Alien minds might not be wholly different from ours, and thus hope exists for a degree of mutual understanding.
In the early 1970’s the Pioneer 10 and 11 spacecraft were launched on the first exploratory missions to the planet Jupiter and beyond. When their missions were completed, these two probes became the first objects made by humans to escape the sun’s gravitational pull and hurtle into interstellar space.
Because of the remote possibility that the spacecraft might someday be found by extraterrestrials, a team of scientists and scholars lead by Carl Sagan emplaced a message on the vehicle, etched on a metal plaque. The message consisted, in part, of a line drawing of a man and a woman. Later, the Voyager 1 and 2 spacecraft carried a message that consisted, in part, of a series of 116 digital images encoded on a phonographic record. The use of images in interstellar communication. In 1977, NASA launched the Voyager 1 and 2 spacecraft on a mission to explore the outer solar system. Destined to wander interstellar space forever following the completion of their mission, each spacecraft carried an interstellar message encoded on a phonographic record. The message, designed by SETI pioneers Carl Sagan and Frank Drake and their collaborators, included 116 digital images. This image is intended to show extraterrestrials how human beings eat and drink. Will extraterrestrials understand such images? The limited quality of the image reflects the state of digital imaging technology in the 70’s National Astronomy and Ionosphere Center, public domain.
The assumption that aliens would see and understand images seems reasonable, since the octopus evolved an eye so similar to our own. And that’s not all. The evolutionary biologists Luitfried Von Salvini-Plawen and Ernst Mayr showed that eyes, of various sorts, have evolved forty separate times on Earth, and vision is typically a dominant sense for large, land dwelling animals. Still, there are animals that function without it, and our earliest mammalian ancestors were nocturnal. Could it be that there are aliens that lack vision, and could not understand a message based on images?
In his short story, The Country of the Blind, the great science fiction writer H. G. Wells imagined an isolated mountain village whose inhabitants had been blind for fifteen generations after a disease destroyed their vision.
A lost mountain climber, finding the village, imagines that with his power of vision, he can easily become their king. But the villagers have adapted thoroughly to a life based on touch, hearing, and smell. Instead of being impressed by their visitor’s claim that he can ‘see’, they find it incomprehensible. They begin to believe he is insane. And when they seek to ‘cure’ him by removing two strange globular growths from the front of his head, he flees. The Mexican blind cavefish (Astyanax mexicanus) has lived in the total darkness of a cave system in central Mexico for more than a million years, and has evolved the loss of its eyes. Astyanax possess a sense that land dwelling animals lack. The lateral line sense, which is present in all fishes, allows these animals to sense their near surroundings based on pressure differences in fields of water flow around their bodies. They also have an acute sense of taste, with taste receptors on their bodies as well as in their mouths. The evolution of cave dwelling intelligent life is probably unlikely, since large brains are metabolically expensive, and food is scarce in caves. On the surface, plants capture energy from sunlight and form the base of the food chain. State Museum of Natural History, Karlsruhe.
Could their really be an alien country of the blind whose inhabitants function without vision? Workshop presenter Dr. Sheri Wells-Jensen, an associate professor of Linguistics at Bowling Green State University, doesn’t need to imagine the country of the blind, because, in a sense, she lives there. She is blind, and believes that creatures without vision could achieve a level of technology sufficient to send interstellar messages. “Sighted people”, she writes, “tend to overestimate the amount and quality of information gathered by vision alone”. Dr. Sheri Wells-Jensen is an associate professor of linguistics at Bowling Green State University. She presented at talk at the Puerto Rico workshop on alternative perceptual systems and interstellar communications. METI International, used with permission.
Bats and dolphins image their dimly lit environments with a kind of naturally occurring sonar called echolocation. Blind human beings can also learn to echolocate, using tongue clicks or claps as emitted signals and analyzing the returning echoes by hearing. Some can do so well enough to ride a bicycle at a moderate pace through an unfamiliar neighborhood. A human can develop the touch sensitivity needed to read braille in four months. A blind marine biologist can proficiently distinguish the species of mollusc shells by touch.
Wells-Jensen posits a hypothetical civilization which she calls the Krikkits, who lack vision but possess sensory abilities otherwise similar to those of human beings. Could such beings build a technological society? Drawing on her knowledge of the blind community and a series of experiments, she thinks they could.
Finding food would present few special difficulties, since blind naturalists can identify many plant species by touch. Agriculture could be conducted as modern blind gardeners do it, by marking crops using stakes and piles of rock, and harvesting by feel. The combination of a stick used as a cane to probe the path ahead and echolocation make traveling by foot effective and safe. A loadstone compass would further aid navigational abilities. The Krikkits might use snares rather than spears or arrows to trap animals, making tools by touch.
Mathematics is vital to building a technological society. For most human beings, with our limited memory, a paper and pencil or a blackboard are essential for doing math. Krikkits would need to find other such aids, such as tactual symbols on clay tablets, abacus-like devices, or patterns sewn on hides or fabric.
Successful blind mathematicians often have prodigious memories, and can perform complex calculations in their heads. One of history’s greatest mathematicians, Leonard Euler, was blind for the last 17 years of his life, but remained mathematically productive through the use of his memory.
The obstacles to a blind society developing technology may not be insurmountable. Blind people are capable of handling fire and even working with molten glass. Krikkits might therefore use fire for cooking, warmth, to bake clay vessels, and smelt metal ores. Initially there only astronomical knowledge would be of the sun as a source of heat. Experiments with loadstones and metals would lead to a knowledge of electricity.
Eventually, the Krikkits might imitate their sonar with radio waves, inventing radar. If their planet possessed a moon or moons, radar reflections from them might provide their first knowledge of astronomical objects other than their sun. Radar would also enable them to learn for the first time that their planet is round.
The Krikkits might learn to detect other forms of radiation like X-rays and ‘light’. The ability to detect this second mysterious form of radiation might allow them to discover the existence of the stars and develop an interest in interstellar communication.
What sorts of messages might they send or understand? Well-Jensen believes that line drawings, like the drawing of the man and the woman on the Pioneer plaque, and other such pictorial representations might be an impenetrable mystery to them. On the other hand, she speculates that Krikkits might represent large data sets through sound, and that their counterpart to charts and graphs might be equally incomprehensible to us.
Images might pose a challenge for the Krikkits, but perhaps, Wells-Jensen concedes, not an impossible one. There is evidence that bats image their world using echolocation. Kikkits might be likely to evolve similar abilities, though Wells-Jensen believes they would not be essential for making tools or handling objects.
Perhaps humans and Krikkits could find common ground by transmitting instructions for three dimensional printed objects that could be explored tactually. Wells-Jensen thinks they might also understand mathematical or logical languages proposed for interstellar communication.
The diversity of cognition and perception that we find here on Earth teaches us that if extraterrestrial intelligence exists, it is likely to be much more alien than much of science fiction has prepared us to expect. In our attempt to communicate with aliens, the gulf of mutual incomprehension may yawn as wide as the gulf of interstellar space. Yet this is a gulf we must somehow cross, if we wish ever to become citizens of the galaxy.
The peahen (at left) and the peacock (at right). The peacock’s elaborate plumage and many other similar animal ornaments posed a troubling difficulty for Charles Darwin in his development of the theory of evolution, since they seemed to have no value for survival. The peacocks that were everywhere present in English gardens were a frustrating and ever-present reminder of the difficulty. “The sight of a feather in a peacock’s tail”, Darwin wrote, “whenever I gaze at it, makes me sick!”. Darwin solved the problem with his theory of sexual selection, which posits that such ornaments evolved because they help animals to woo mates, and thereby pass the trait into the next generation. Since mating in peafowl is by female choice, elaborate tail feathers are vital to the peacock, but unnecessary to the peahen. Sexual selection is increasingly recognized as a central evolutionary process by modern biologists. Evolutionary psychologist Dr. Geoffrey Miller posits that the enormous human brain evolved by sexual selection through the choices of both genders. Understanding how human intelligence evolved here on Earth is critical to understanding whether or not alien civilizations are likely to exist. Picture is from the Miho Museum, Shiga, Japan, 1781, public domain.
In the first instalment of this series, we saw that intelligence, of various sorts, is widespread across the animal kingdom. Workshop presenter Anna Dornhaus, who studies collective decision-making in insects as an associate professor at the University of Arizona, showed that even insects, with their diminutive brains, exhibit a surprising cognitive sophistication. Intelligence, of various sorts, is a likely and probable evolutionary product.
Animals evolve the cognitive abilities that they need to meet the demands of their own particular environments and lifestyles. Sophisticated brains and cognition have evolved many times on Earth, in many separate evolutionary lineages. But, of the millions of evolutionary lineages that have arisen on Earth in the 600 million years since complex life appeared, only one, that which led to human beings, produced the peculiar combination of cognitive traits that led to a technological civilization. What this tells us is that technological civilization is not the inevitable product of a long term evolutionary trend, it is rather the quirky and contingent product of particular circumstances. But what might those circumstances have been, and just how special and improbable were they?
Dr. Geoffery Miller is an associate professor of psychology at the University of New Mexico, and is the author of a 2001 book, The Mating Mind, where he explains his theory that human intelligence evolved by sexual selection to a general audience. He presented at the METI Institute conference in Puerto Rico, in May 2016. Picture used with permission.
Workshop presenter Geoffrey Miller is an associate professor of psychology at the University of New Mexico. Miller thinks he has an answer to the question of what the special circumstances that produced human evolution were. Our protohuman ancestors inhabited the African savanna. But so do many other mammals that don’t need enormous brains to survive there. The evolutionary forces driving the production of our large brains, Miller surmises, can’t be due to the challenges of survival. He thinks instead that human evolution was guided by an intelligence. But Miller is no creationist, nor does he have the alien monolith from the 1960’s science fiction classic 2001: A Space Odyssey in mind. Miller’s guiding intelligence is the intelligence that our ancestors themselves used when they selected their mates.
Miller’s theory harkens back to the ideas of the founder of modern evolutionary theory, the nineteenth century British naturalist Charles Darwin. Darwin proposed that evolution works through a process of natural selection. Animal offspring vary one from another, and are produced in too great of numbers for all of them to survive. Some starve, some are eaten by predators, others fall prey to the numerous other hazards of the natural world. A few survive to produce offspring, thereby passing on the traits that allowed them to survive. Down the generations, traits that aided survival become more elaborate and useful and traits that did not, vanished. Charles Darwin published his theory of evolution, in his book, The Origin of Species, in 1859. The theory was inspired, in part, by observations he made during his five year voyage as a naturalist on board the HMS Beagle and has become the central principle of much of modern biology. Picture by George Richmond (1830’s) public domain.
But Darwin was troubled by a serious problem with his theory. He knew that many animals have prominent traits that don’t seem to contribute to their survival, and are even counterproductive to it. The bright colors of many insects, the colors, elaborate plumage, and songs of birds, the huge antlers of elk, were all prominent and costly traits that couldn’t be explained by his theory of natural selection. Peacocks, with their elaborate tail feathers were everywhere in English gardens, and came to torment him.
At last, Darwin found the solution. To produce offspring, an animal must do more than just survive, it must find a partner to mate with. All the traits which worried Darwin could be explained if they served to make their bearers sexier and more beautiful to prospective mates than other competing members of their own gender. If peahens like elaborate plumage, then in each generation, they will choose to mate with the males with the most elaborate tail feathers, and reject the rest. Through the competition for mates, peacock tails will become more and more elaborate down the generations. Darwin called his new theory sexual selection.
Many subsequent evolutionary biologists regarded sexual selection as of limited importance, and lumped it in with natural selection, which was said to favor traits conducive to survival and reproductive success. However, in recent decades evolutionary biologists have come to view sexual selection in a much more favorable light. Geoffrey Miller proposed that the human brain evolved through sexual selection. Human beings, he supposes, are sapiosexual; that is, they are sexually attracted by intelligence and its products. The preference for selecting intelligent mates produced greater intelligence, which in turn allowed our ancestors to become more discerning in selecting more intelligent mates, producing a kind of amplifying feedback loop, and an explosion of intelligence.
On this account, language, music, dancing, humor, art, literature, and perhaps even morality and ethics exist because those who were good at them were deemed sexier, or more trustworthy and reliable, and were thus more successful in securing mates than those who weren’t. The elaborate human brain is like the elaborate peacock’s tail. It exists for wooing mates and not for survival. There are some important ways in which protohumans were different from peafowl. Both males and females are choosy and both have large brains. Protohumans, unlike peafowl, probably formed monogamous pair bonds. Miller’s theory has complexities that space won’t permit us to explore here. To show that his theory can work, Miller needed to develop a computer model.
The evolution of protohuman intelligence through geography and time. Homo egaster lived in the early Pleistocene between 1.9 and 1.4 million years ago and had a brain about half the size of modern Homo sapiens. It developed advanced stone tools, and may have domesticated fire. It was closely related to Homo erectus. Homo antecessor lived from 1.2 million to 800,000 years ago and spread from Africa into Europe. It’s brain was also about half as large as that of ours. Homo rhodesiensis lived about 120,000 to 300,000 years ago. Our species, Homo sapiens, arose in Africa about 200,000 years ago and spread throughout much of the world. Homo neanderthalensis had a brain capacity somewhat larger than that of modern humans, and its larger eye sockets suggest keener vision. They disappeared about 30,000 years ago, and may have died out, in part, through competition with Homo sapiens and cooling of the climate. Public Library of Science 2003.
If Miller is right, then just how probable is the evolution of a technological civilization, and how likely is it that we will find them elsewhere in the galaxy? Miller thinks that if complex life exists on other planets or moons, it is likely to evolve reproduction through sex, just as has happened here on Earth. For complex organisms that depend on a large and complicated body of genetic information, most mutations will be neutral or harmful. In sexual reproduction half the genes of one’s offspring come from each parent. Without this mixing of genes from other individuals, asexual lineages are likely to falter and go extinct due to an accumulation of harmful mutations. Unless sexually reproducing creatures choose their mates purely at random, sexual selection is an inevitability. So, the basic conditions for runaway sexual selection to produce a brain suited to language and technology probably exists on other worlds with complex life.
One problem, though, that Anna Dornhaus pointed out, is that in sexual selection, the trait that gets exaggerated is essentially arbitrary. There are many bird species with elaborate plumage, but none exactly like the peacock. There are many species where brains and cognitive traits matter for mating success, like the singing ability of nightingales and many other birds, or gibbons, or whales. Male bower birds build complicated structures, called bowers, out of found items, like sticks and leaves and stones and shells, to attract a female. Chimpanzees engage in complex power struggles that involve negotiation, grooming, and fighting their way to the top.
But despite the selective success of cognition and braininess in many species, our specific human sort of intelligence, with language and technology, has happened only once on Earth, and therefore might be rare in the universe. If our ancestors had found big noses rather than big brains sexy, then we might now have enormous noses rather than enormous radio telescopes capable of signaling to other worlds.
Miller is more optimistic. “It’s a rare accident” he writes, in the sense that mate preferences only rarely turn ‘sapiosexual’, focused so heavily on conspicuous displays of general intelligence… On the other hand, I think it’s likely that in any biosphere, sexual selection would eventually stumble into sapiosexual mate preferences, and then you’d get human-level intelligence and language of some sort. It might only arise in 1 out of every 100 million species though,…I suspect that in any biosphere with sexually reproducing complex organisms and a wide variety of species, you’d quite likely get at least one lineage stumbling into the sapiosexual niche within a billion years”.
A planet or moon is currently deemed potentially habitable if it orbits its parent star within the right distance range for liquid water to exist on its surface. This distance range is called the habitable zone. Since stars evolve with time, the duration of habitability is limited. Such matters can be explored through climate modeling, informed by what we know of the climates of Earth and other worlds within our solar system, and about the evolution of stars.
Current thinking is that Earth’s total duration of habitability is 6.3 to 7.8 billion years, and that our world may remain habitable for another 1.75 billion years. Since complex life has already existed on Earth for 600 million years, this seems a generous amount of time for complex life on a similar planet to stumble upon Miller’s sapiosexual niche. Stars of smaller mass than the sun are stable on longer timescales, some perhaps capable of sustaining worlds with liquid water for a hundred billion years. If Miller’s estimates are reasonable, then there may be worlds enough and time for an abundance of sapiosexual alien civilizations in our galaxy.
A central message of the METI Institute workshop is that, animals evolve whatever sort of intelligence is necessary for them to survive and reproduce under the circumstances in which they find themselves. Human-style intelligence, with language and technology, is a peculiar quirk of particular and improbable evolutionary circumstances. But we don’t know just how improbable. Given the vastness of time and number of worlds potentially available for the roll of the evolutionary dice, alien civilizations might be reasonably abundant, or they might be once-in-a-billion galaxies rare. We just don’t know. Better knowledge of the evolution of life and intelligence here on Earth might allow us to improve our estimates.
If alien civilizations do exist, what can life on Earth tell us about what their minds and senses are likely to be like? Are they, like us, visually oriented creatures, or might they rely on other senses? Can we expect that their minds might be similar enough to ours to make meaningful communication possible? These intriguing questions will be the subject of the third and final installment of this series.
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.
METI International
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).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.
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.
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.
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.
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.
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 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. 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.
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.
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.
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.
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.
