Scientists studying life on Mars got a late Christmas present this year: confirmation that meteorites found in Morocco in December are of Martian origin. It’s a significant discovery; Martian meteorites fall to Earth only about once every 50 years making this a once-in-a-lifetime, and for many a once-in-a-career, event. The Mars rocks are worth more than their weight in gold, but what they can tell us could be even more valuable.
Astronomers suspect that the meteorite has been wandering around the solar system for millions of years, ever since something big smashed into the red planet and sent debris flying all directions. One of those pieces has wandered its way towards Earth and plunged through the atmosphere.
ALH 84001, the meteorite found in Antarctica in 1984. Evidence of fossilized life inside the rock sparked a search for life on Mars. Image credit: NASA/ JSC
This is only the fifth time scientists have chemically confirmed the Martian origin of meteorites. Rocks found in France in 1815, in India in 1865, in Egypt in 1911, and in Nigeria in 1962 have all been positively identified as being from Mars.
The chemical signature of the Moroccan rocks and the Martian air match said Tony Irving of the University of Washington who did the scientific analysis. But this discovery is different. The rocks weren’t just found, they were seen streaking through the sky in July 2011, which makes them extremely valuable.
These rocks have only had six months to accumulate Earth-based materials and traces of life; typically Martian meteorites found on Earth have been here anywhere from decades to millennia, giving them ample time to become tainted.
These new rocks, while still contaminated because they have been on Earth for months, are relatively pure. “It’s incredibly fresh. It’s highly valuable for that reason,” said Carl Agee, director of the Institute of Meteoritics and curator at the University of New Mexico.
It’s also a rare find. This new sample, about 15 pounds of rocks, brings the total weight of all Martian samples on Earth to just 240 pounds.
Meteorite dealer Darryl Pitt is cashing in on the rocks’ rarity and selling pieces for $11,000 to $22,500 an ounce and has sold most of his supply already. At that price, the Martian meteorite costs about 10 times as much as gold.
An artist's conception of early Mars being hit by an asteroid wider than Texas. Scientists believe the impact melted the planet's crust in its northern hemisphere, flung crust into space, and sent shock wave through the planet's molten core (inset). This explains why Mars' crust is thinner in the northern hemisphere, according to three new studies. Image courtesy Jeff Andrews-Hanna; inset courtesy Francis Nimmo.
Cornell University astronomer Steve Squyres, the principal investigator for NASA’s Mars Exploration Rover Program, is less excited. The rocks, he said, are not the kind scientists are most hoping for. They are hard, igneous or volcanic rock. A softer kind of rock capable of holding water or life would be better. But he also points that these rocks aren’t likely to come streaking through the atmosphere. Any soft rock would be unlikely to survive the fiery entry through Earth’s atmosphere.
Former NASA sciences chief Alan Stern, director of the Florida Space Institute at the University of Central Florida, takes a brighter outlook. “It’s nice to have Mars sending samples to Earth,” he said, “particularly when our pockets are too empty to go get them ourselves.”
Until we manage a sample return mission from Mars, this is the best shot scientists have to study the red planet up close.
The search for extraterrestrial life outside our Solar System is currently focused on extrasolar planets within the ‘habitable zones’ of exoplanetary systems around stars similar to the Sun. Finding Earth-like planets around other stars is the primary goal of NASA’s Kepler Mission.
The habitable zone (HZ) around a star is defined as the range of distances over which liquid water could exist on the surface of a terrestrial planet, given a dense enough atmosphere. Terrestrial planets are generally defined as rocky and similar to Earth in size and mass. A visualization of the habitable zones around stars of different diameters and brightness and temperature is shown here. The red region is too hot, the blue region is too cold, but the green region is just right for liquid water. Because it can be described this way, the HZ is also referred to as the “Goldilocks Zone”.
Normally, we think of planets around other stars as being similar to our solar system, where a retinue of planets orbits a single star. Although theoretically possible, scientists debated whether or not planets would ever be found around pairs of stars or multiple star systems. Then, in September, 2011, researchers at NASA’s Kepler mission announced the discovery of Kepler-16b, a cold, gaseous, Saturn-sized planet that orbits a pair of stars, like Star Wars’ fictional Tatooine.
This week I had the chance to interview one of the young guns studying exoplanets, Billy Quarles. Monday, Billy and his co-authors, professor Zdzislaw Musielak and associate professor Manfred Cuntz, presented their findings on the possibility of Earth-like planets inside the habitable zones of Kepler 16 and other circumbinary star systems, at the AAS meeting in Austin, Texas.
The Goldilocks Zones around various type stars. Credit: NASA/JPL-Caltech
“To define the habitable zone we calculate the amount of flux that is incident on an object at a given distance,” Billy explained. “We also took into account that different planets with different atmospheres will retain heat differently. A planet with a really weak greenhouse effect can be closer in to the stars. For a planet with a much stronger greenhouse effect, the habitable zone will be further out.”
“In our particular study, we have a planet orbiting two stars. One of the stars is much brighter than the other. So much brighter, that we ignored the flux coming from the smaller fainter companion star altogether. So our definition of the habitable zone in this case is a conservative estimate.”
Quarles and his colleagues performed extensive numerical studies on the long-term stability of planetary orbits within the Kepler 16 HZ. “The stability of the planetary orbit depends on the distance from the binary stars,” said Quarles. “The further out the more stable they tend to be, because there is less perturbation from the secondary star.”
For the Kepler 16 system, planetary orbits around the primary star are only stable out to 0.0675 AU (astronomical units). “That is well inside the inner limit of habitability, where the runaway greenhouse effect takes over,” Billy explained. This all but rules out the possibility of habitable planets in close orbit around the primary star of the pair. What they found was that orbits in the Goldilocks Zone farther out, around the pair of Kepler 16’s low-mass stars, are stable on time scales of a million years or more, providing the possibility that life could evolve on a planet within that HZ.
Kepler 16's orbit from Quarles et al
Kepler 16b’s roughly circular orbit, about 65 million miles from the stars, is on the outer edge of this habitable zone. Being a gas giant, 16b is not a habitable terrestrial planet. However, an Earth-like moon, a Goldilocks Moon, in orbit around this planet could sustain life if it were massive enough to retain an Earth-like atmosphere. “We determined that a habitable exomoon is possible in orbit around Kepler-16b,” Quarles said.
I asked Quarles how stellar evolution impacts these Goldilocks Zones. He told me, “There are a number of things to consider over the lifetime of a system. One of them is how the star evolves over time. In most cases the habitable zone starts out close and then slowly drifts out.”
During a star’s main sequence lifetime, nuclear burning of hydrogen builds up helium in its core, causing an increase in pressure and temperature. This occurs more rapidly in stars that are more massive and lower in metallicity. These changes affect the outer regions of the star, which results in a steady increase in luminosity and effective temperature. The star becomes more luminous, causing the HZ to move outwards. This movement could result in a planet within the HZ at the beginning of a star’s main sequence lifetime, to become too hot, and eventually, uninhabitable. Similarly, an inhospitable planet originally outside the HZ, may thaw out and enable life to commence.
“For our study, we ignored the stellar evolution part,” said lead author, Quarles. “We ran our models for a million years to see where the habitable zone was for that part of the star’s life cycle.”
Being at the right distance from its star is only one of the necessary conditions required for a planet to be habitable. Habitable conditions on a planet require various geophysical and geochemical conditions. Many factors can prevent, or impede, habitability. For example, the planet may lack water, gravity may be too weak to retain a dense atmosphere, the rate of large impacts may be too high, or the minimum ingredients necessary for life (still up for debate) may not be there.
One thing is clear. Even with all the requirements for life as we know it, there appear to be plenty of planets around other stars, and very likely, Goldilocks Moons around planets, orbiting within the habitable zones of stars in our galaxy, that detecting the signature of life in the atmosphere of a planet or moon around another Sun seems like only a matter of time now.
Hydrothermal vents deep in Earth's oceans. Could similar types of vents power the transport of silica and other materials out from Enceladus? Credit: NOAA
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Scientists have recently discovered communities of previously unknown species living on the seafloor near Antarctica clustered around hydrothermal vents. This discovery is certainly exciting for biologists, but it’s also important for astrobiologists. It begs the question — if life can thrive in the deep, dark oceans without sunlight, could similar life thrive elsewhere in our solar system or the universe?
For decades, scientists assumed the deep oceans were barren; sunlight can’t reach the ocean floor, making it an impossible environment for life as we know it to arise. But in 1977, oceanographers from the Scripps Institute discovered hydrothermal vents.
A schematic diagram of deep sea vent chemistry. Image credit: National Oceanic and Atmospheric Administration
These fissures, found along mid-ocean ridges on the seafloor of the Pacific, Atlantic, and Indian Oceans, create a natural, deep-sea plumbing system. Heat and minerals from the Earth’s interior vents out, providing a complex ecosystem that can reach up to 382 degrees Celsius (almost 720 degrees Fahrenheit). These ecosystems can support unique life forms that get their energy not from the Sun but from breaking down chemicals issued from the vents such as hydrogen sulphide.
The latest life forms, discovered in the Antarctic region by teams from the University of Oxford, University of Southampton and British Antarctic Survey, include a new species of yeti crab, starfish, barnacles, sea anemones, and potentially an octopus.
“These findings are yet more evidence of the precious diversity to be found throughout the world’s oceans,” said Professor Rogers of Oxford University’s Department of Zoology. “Everywhere we look, whether it is in the sunlit coral reefs of tropical waters or these Antarctic vents shrouded in eternal darkness, we find unique ecosystems that we need to understand and protect.”
Jupiter's moon Europa. The lines on the surface are breaks in the ice that lie on top of vast oceans. Image credit: NASA/courtesy of nasaimages.org
But it isn’t only biologists studying life on Earth that can benefit from this latest discovery. These peculiar environments on and beneath the seafloor could be a model for the origin of life on Earth and on other planets.
One particular target is Jupiter’s moon Europa. Recent research has confirmed that the moon has vast oceans buried beneath its frozen surface ice; it’s estimated to hold twice as much water as Earth. As such, it is a target for NASA in the search for life. It could be the case that some type of hydrothermal vent system exists on Europa, making its distance from the Sun irrelevant for life.
But just because sulfur or methane-based life on Earth can thrive around deep-ocean vents doesn’t mean the same is true on Europa. The presence of hydrothermal vents depends on geologic activity and a hot interior, neither of which has been confirmed. The possibility remains that light energy from the Sun could travel the distance to the moon and provide shallower portions of the subsurface oceans with life-giving light.
In any case, as scientists discover life in the more extreme environments on Earth, analogies are drawn with other worlds. If life is discovered in hostile parts of our planet, the same could theoretically arise in similar environments on other worlds.
The "Blair Cuspids" spires photographed by Lunar Orbiter 2 in 1966. Credit: NASA
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Two researchers at Arizona State University (ASU) have made a rather controversial proposal: have the public and other researchers study the high-resolution photographs of the Moon already being taken by the Lunar Reconnaissance Orbiter (LRO), to look for anomalies that may possibly be evidence of artifacts leftover from previous alien visitation. The theory is that if our solar system had been visited in the past, the Moon would have made an ideal base from which to study the Earth. The paper has just been recently published in the journal Acta Astronautica.
Professor Paul Davies and research technician Robert Wagner admit that the chances of success are very small, but argue that the endeavour would be worth the minimal investment required. The photographs are already being taken on a regular basis by LRO. Any interesting finds could be examined by others including imaging professionals. Shape-recognizing software could also be used to help discern any possible artificial artifacts from natural ones.
From the abstract:
The Search for Extraterrestrial Intelligence (SETI) has a low probability of success, but it would have a high impact if successful. Therefore it makes sense to widen the search as much as possible within the confines of the modest budget and limited resources currently available. To date, SETI has been dominated by the paradigm of seeking deliberately beamed radio messages.
However, indirect evidence for extraterrestrial intelligence could come from any incontrovertible signatures of non-human technology. Existing searchable databases from astronomy, biology, earth and planetary sciences all offer low-cost opportunities to seek a footprint of extraterrestrial technology. In this paper we take as a case study one particular new and rapidly-expanding database: the photographic mapping of the Moon’s surface by the Lunar Reconnaissance Orbiter (LRO) to 0.5 m resolution. Although there is only a tiny probability that alien technology would have left traces on the moon in the form of an artifact or surface modification of lunar features, this location has the virtue of being close, and of preserving traces for an immense duration.
Systematic scrutiny of the LRO photographic images is being routinely conducted anyway for planetary science purposes, and this program could readily be expanded and outsourced at little extra cost to accommodate SETI goals, after the fashion of the SETI@home and Galaxy Zoo projects.
Of course, it has been said by some that such artifacts have already been found and known about for decades but hidden from the public by NASA, et al. An entire cottage industry has grown around this idea. There are actually a handful of anomalies from various missions that would be interesting to see at much higher resolution via LRO, such as the well-known “Blair Cuspids” photographed by Lunar Orbiter 2 in 1966, although by far most unusual-looking objects are easily explained. It’s the same problem as with Mars; so many anomalies found by amateur observers are the product of pareidolia, lighting effects, image defects or even geology. Separating out any genuine anomalies from all of the noise would be a tedious and time-consuming task. On the other hand, we now have much better cameras in orbit around the Moon (and Mars) and more advanced photographic analysis techniques available.
Yes, the chances of finding anything are very small, maybe even nonexistent in the opinion of some, but if we have the images being taken anyway, and the willingness of some to study them, then why not? If nothing is found, no harm done. It something was found, well that’s another story entirely…
The abstract for the paper is here. (The paper itself costs $31.50 US to download).
Engineers tuck Phobos-Grunt into the rocket fairing. Credit: Roscosmos
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According to a news report in RiaNovosti, Russia’s Phobos-Grunt spacecraft will fall January 14th, “somewhere between 30.7 degrees north and 62.3 degrees east,” placing debris near the city of Mirabad, in southwestern Afghanistan. RiaNovosti said this prediction is according to the United States Strategic Command who calculated the craft will reenter Earth’s atmosphere at 2:22 am.
Editor’s Update: In a call to USSTRATCOM to verify this information, a spokesperson said, “We are not making any statement at USSTRACOM at this time because we are not the lead for this event and cannot make an official statement for any predictions or what is releasable at this time.”
“Please note that the U.S. Strategic Command prediction had a large uncertainty associated with it, i.e., 11 days,” Nicholas L. Johnson, NASA’s Chief Scientist for Orbital Debris told Universe Today in an email. “No one is yet able to predict with confidence the day the Phobos-Grunt will reenter.”
If the probe is predicted to fall on land, this raises the possibility of recovering the Planetary Society’s Living Interplanetary Flight Experiment (LIFE), designed to investigate how life forms could spread between neighboring planets.
The Phobos-Grunt mission profile. Credit: Roscosmos
Carrying about 50 kilograms of scientific equipment, the unpiloted Phobos-Grunt probe was launched November 9th on a mission to the larger of Mars two small moons. Although the Zenit 2 rocket that launched the craft functioned flawlessly, sending Grunt into a low Earth orbit, the upper stage booster, known as Fregat, failed to boost the orbit and send it on a trajectory toward Mars. Thought to have reverted to safe mode, Phobos-Grunt has been flying straight and periodically adjusting her orbit using small thruster engines. While this maneuvering has extended the amount of time that the probe could remain in space before reentering Earth’s atmosphere, ground controllers have been struggling to establish a communication link.
For a while, space commentators considered the possibility that Grunt might be sent on an alternate mission to Earth’s Moon or an asteroid, if control could be restored after the window for a launch to Mars and Phobos was lost. During the past few weeks, the European Space Agency (ESA) started and ended efforts to communicate with the spacecraft on several occasions, but succeeded only twice. Various scenarios were imagined in which aspects of the probe’s mission could be salvaged, despite the serious malfunction that prevented the craft from leaving Earth orbit. But at this point, the only direction for the spacecraft to go is down.
In addition to equipment for making celestial and geophysical measurements and for conduct mineralogical and chemical analysis of the Phobosian regolith (crushed rock and dust), Grunt carries Yinhou-1, a Chinese probe that was to orbit Mars for two years. After releasing Yinhou-1 into Mars orbit and landing on Phobos, Grunt would have launched a return capsule, carrying a 200 gram sample of regolith back to Earth. Also traveling within the return capsule is the Planetary Society’s Living Interplanetary Flight Experiment (LIFE).
The Planetary Society’s Living Interplanetary Flight Experiment (LIFE) capsule, on board the Phobos-Grunt spacecraft. Credit:The Planetary Society
Specifically, LIFE is designed to study the effects of the interplanetary environment on various organisms during a long duration flight in space beyond the Van Allen Radiation Belts, which protect organisms in low Earth orbit from some of the most powerful components of space radiation. Although the spacecraft has not traveled outside of the belts, the organisms contained within the LIFE biomodule will have been in space for more than two months when the probe reenters the atmosphere.
The many tons of toxic fuel are expected to explode high in the atmosphere. However, since the return capsule is designed to survive the heat of reentry and make a survivable trajectory to the ground, it is quite possible that it will reach Afghanistan in one piece. Because the LIFE biomodule is designed to withstand an impact force of 4,000 Gs, it is possible that the experiment can be recovered and the biological samples studied.
To be sure, the possibility of recovering an unharmed returned capsule and LIFE depends on the willingness of the inhabitants around the landing site to allow the Russian Space Agency to pick it up. Given the proximity of the predicted landing area to a war zone and the fact that the Taliban are not known for being enthusiastic about space exploration and astrobiology, it is also possible that a landing on land could turn out no better than a landing over the deepest part of the ocean.
The question of whether present-day Mars could be habitable, and to what extent, has been the focus of long-running and intense debates. The surface, comparable to the dry valleys of Antarctica and the Atacama desert on Earth, is harsh, with well-below freezing temperatures most of the time (at an average of minus 63 degrees Celsius or minus 81 Fahrenheit), extreme dryness and a very thin atmosphere offering little protection from the Sun’s ultraviolet radiation. Most scientists would agree that the best place that any organisms could hope to survive and flourish would be underground. Now, a new study says that scenario is not only correct, but that large regions of Mars’ subsurface could be even more sustainable for life than previously thought.
Scientists from the Australian National University modeled conditions on Mars on a global scale and found that large regions could be capable of sustaining life – three percent of the planet actually, albeit mostly underground. By comparison, just one percent of Earth’s volume, from the central core to the upper atmosphere, is inhabited by some kind of life. They compared pressure and temperature conditions on Earth to those of Mars to come up with the surprising results.
According to Charley Lineweaver of ANU, “What we tried to do, simply, was take almost all of the information we could and put it together and say ‘is the big picture consistent with there being life on Mars?’ And the simple answer is yes… There are large regions of Mars that are compatible with terrestrial life.”
So it seems that while, as we know, the surface of Mars is quite inhospitable to most forms of life (that we know of) except perhaps for some extremophiles, conditions underground are a different matter. It is already known that there are vast deposits of ice below the surface even near the equator (as well as the polar ice caps of course), so there could be liquid water a bit deeper where it is warmer. Those conditions would be ideal for bacteria or other simple organisms. While that idea has been proposed and discussed before, Lineweaver’s findings support it on a planet-wide basis – previous studies tended to focus on specific locations in a “piecemeal” approach, but these new ones take the entire planet into consideration.
The paper is currently available for free here. Abstract:
We present a comprehensive model of martian pressure-temperature (P-T) phase space and compare it with that of Earth. Martian P-T conditions compatible with liquid water extend to a depth of *310 km. We use our phase space model of Mars and of terrestrial life to estimate the depths and extent of the water on Mars that is habitable for terrestrial life. We find an extensive overlap between inhabited terrestrial phase space and martian phase space. The lower martian surface temperatures and shallower martian geotherm suggest that, if there is a hot deep biosphere on Mars, it could extend 7 times deeper than the *5km depth of the hot deep terrestrial biosphere in the crust inhabited by hyperthermophilic chemolithotrophs. This corresponds to *3.2% of the volume of present-day Mars being potentially habitable for terrestrial-like life. Key Words: Biosphere—Mars— Limits of life—Extremophiles—Water. Astrobiology 11, xxx–xxx.
Anyone who has an interest in exoplanets probably knows about the various online catalogs that have become available in recent years, such as The Extrasolar Planets Encyclopaedia for example, providing up-to-date information and statistics on the rapidly growing number of worlds being discovered orbiting other stars. So far, these have been listings of all known exoplanets, both candidates and confirmed. But now there is a new catalog published by the Planetary Habitability Laboratory (a project of the University of Puerto Rico at Arecibo), which focuses exclusively on those planets which have been determined to be potentially habitable. The Habitable Exoplanets Catalog is a database which will serve as a key resource for scientists and educators as well as the general public.
As of right now, there are two confirmed planets and fourteen candidates listed, but those numbers are expected to grow over the coming months and years as more candidates are found and more of those candidates are confirmed. There is even a listing of habitable moons, whose existence have been inferred from the data, although none have been observed yet (finding exoplanets is challenging enough, but exomoons even more so!).
According to Abel Méndez, Director of the PHL and principal investigator, “One important outcome of these rankings is the ability to compare exoplanets from best to worst candidates for life.” He adds: “New observations with ground and orbital observatories will discover thousands of exoplanets in the coming years. We expect that the analyses contained in our catalog will help to identify, organize, and compare the life potential of these discoveries.”
The big question of course is whether any habitable planets are actually inhabited, two different things. To help answer that, it will be necessary to further analyze the atmospheres and surfaces of those planets, looking for any indication of possible biosignatures such as oxygen or methane. Kepler can’t do that directly, but subsequent telescopes such as the Terrestrial Planet Finder (TPF) will be able to, and provide a more accurate assessment of their physical composition, climate, etc.
Not long ago it wasn’t known if there even were any planets orbiting other stars; now we’re finding them by the thousands and soon we’ll be able to distinguish their unique physical characteristics and have a better idea of how many habitable worlds are out there – exciting times.
This artist's illustration of Kepler 22-b, an Earth-like planet in the habitable zone of a Sun-like star about 640 light years (166 parsecs) away. Credit: NASA/Ames/JPL-Caltech
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Scientists from the Kepler mission announced this morning the first confirmed exoplanet orbiting in the habitable zone of a Sun-like star, the region where liquid water could exist on the surface of a rocky planet like Earth. Evidence for others has already been found by Kepler, but this is the first confirmation. The planet, Kepler-22b, is also only about 2.4 times the radius of Earth — the smallest planet found in a habitable zone so far — and orbits its star, Kepler-22, in 290 days. It is about 600 light-years away from Earth, and Kepler-22 is only slightly smaller and cooler than our own Sun. Not only is the planet in the habitable zone, but astronomers have determined its surface temperature averages a comfortable 22 degrees C (72 degrees F). Since the planet’s mass is not yet known, astronomers haven’t determined if it is a rocky or gaseous planet. But this discovery is a major step toward finding Earth-like worlds around other stars. A very exciting discovery, but there’s more…
It was also announced that Kepler has found 1,094 more planetary candidates, increasing the number now to 2,326! That’s an increase of 89% since the last update this past February. Of these, 207 are near Earth size, 680 are super-Earth size, 1,181 are Neptune size, 203 are Jupiter size and 55 are larger than Jupiter. These findings continue the observational trend seen before, where smaller planets are apparently more numerous than larger gas giant planets. The number of Earth size candidates has increased by more than 200 percent and the number of super-Earth size candidates has increased by 140 percent.
According to Natalie Batalha, Kepler deputy science team lead at San Jose State University in San Jose, California, “The tremendous growth in the number of Earth-size candidates tells us that we’re honing in on the planets Kepler was designed to detect: those that are not only Earth-size, but also are potentially habitable. The more data we collect, the keener our eye for finding the smallest planets out at longer orbital periods.”
Regarding Kepler-22b, William Borucki, Kepler principal investigator at NASA Ames Research Center at Moffett Field, California stated: “Fortune smiled upon us with the detection of this planet. The first transit was captured just three days after we declared the spacecraft operationally ready. We witnessed the defining third transit over the 2010 holiday season.”
Comparison of the Kepler-22 system with our own inner solar system. Credit: NASA/Ames/JPL-Caltech
Previously there were 54 planetary candidates in habitable zones, but this was changed to 48, after the Kepler team redefined the definition of what constitutes a habitable zone in order to account for the warming effects of atmospheres which could shift the zone farther out from a star.
The announcements were made at the inaugural Kepler science conference which runs from December 5-9 at Ames Research Center.
See also the press release from the Carnegie Institution for Science here.
Conventional wisdom has long had it that carbon-based life, so common here on earth, must surely be abundant elsewhere; both in our galaxy and the universe as a whole.
This line of reasoning is founded on two major assumptions; the first being that complex carbon chain molecules, the building blocks of life as we know it, have been detected throughout the interstellar medium. Carbon’s abundance appears to stretch across much of cosmic time, since its production is thought to have peaked some 7 billion years ago, when the universe was roughly half its current age.
The other major assumption is that life needs an elixir, a solvent on which it can advance its unique complex chemistry. Water and carbon go hand in hand in making this happen.
While the world as we know it runs on carbon, science fiction’s long flirtation with silicon-based life — “It’s life, but not as we know it” — has become a familiar catchphrase. But life of any sort should evolve, eat, excrete, reproduce, and respond to stimulus.
And although non-carbon based life is a very long shot, we thought we’d broach the issue with one of the country’s top astrochemists — Max Bernstein, the Research Lead of the Science Mission Directorate at NASA headquarters in Washington,D.C.
Bruce Dorminey — IS IT WRONG TO ASSUME THAT LIFE COULD BE BASED ON SOMETHING OTHER THAN CARBON?
Max Bernstein. Credit: NASA
Max Bernstein — It’s important for us to keep an open mind about alien life, lest we come across it and miss it. On the other hand, carbon is much better than any other element in forming the main structures of living things. Carbon can form many stable complex structures of great diversity. When carbon forms molecules containing cxygen and nitrogen, the carbon bonds to nitrogen and oxygen are stable. But not so much so that they can’t be fairly easily undone, unlike silicon-oxygen bonds, for example.
Dorminey — DOES THE RECENT NASA-FUNDED RESEARCH AT MONO LAKE, CALIFORNIA WHICH TOUTED THE DISCOVERY OF BACTERIA WITH DNA THAT USES ARSENIC INSTEAD OF PHOSPHORUS RATTLE THE CURRENT PARADIGM?
Bernstein — That was a really cool result, but the basic structure was still carbon. The arsenic was said to have replaced phosphorus, not carbon. The discovery of this putative arsenic organism may prove to be incorrect, but it’s a hypothesis with science behind it, and not just someone tossing out an idea and leaving it at the level of what if you replaced carbon with silicon?
The structure of silane, the silicon-based analogue of methane.
Dorminey — SILICON SEEMS TO BE THE MOST POPULAR NON-CARBON BASED CANDIDATE, ARE THERE OTHERS THAT ALSO MIGHT BE FEASIBLE?
Bernstein — It’s hard to imagine anything that would be more likely that silicon because there is nothing closer to carbon than silicon in terms of its chemistry. It’s in the right place on the periodic table, just below carbon. On the face of it, [silicon-based life] doesn’t seem too absurd since silicon, like carbon, forms four bonds. CH4 is methane and SiH4 is silane. They are analogous molecules so the basic idea is that perhaps silicon could form an entire parallel chemistry, and even life. But there are tons of problems with this idea. We don’t see a complex stable chemistry [solely] of silicon and hydrogen, as we see with carbon and hydrogen. We use hydrocarbon chains in our lipids (molecules that make up membranes), but the analogous silane chains would not be stable. Whereas carbon-oxygen bonds can be made and unmade — this goes on in our bodies all the time — this is not true for silicon. This would severely limit silicon’s life-like chemistry. Maybe you could have something silicon-based that’s sort of alive, but only in the sense that it passes on information.
Dorminey — IF SILICON-BASED LIFE IS OUT THERE, HOW COULD WE EVER DETECT IT REMOTELY?
Bernstein — We are seriously arguing about how we would remotely detect life just like us, so I really couldn’t say. Presumably technology-using organisms, whatever their biochemistry, will produce technology, so the Search for Extraterrestrial Intelligence (SETI) may be our best shot.
Dorminey— HOW WOULD YOU LOOK FOR SILICON-BASED LIFE HERE ON EARTH?
Bernstein — When seeking an alien organism its really tough because you just don’t know what molecules to look for. One would have to be satisfied by something a bit more ambiguous, like sets of molecules that should not be there. For example, if you were an alien Silicon organism, you might not be looking for our biochemistry, but the fact that you kept seeing exactly the same chain lengths over and over again might tip you off to the fact that those darn carbon chains might actually be the basis of an organism’s membranes.
Dorminey — WHERE ARE THE LARGEST CONCENTRATIONS OF SILICON HERE?
IN SAND?
Bernstein — In sand or rock. There are literally megatons of silicate minerals on Earth.
Dorminey — HAS ANYONE EVER CLAIMED DETECTION OF SELF-REPLICATING EXAMPLES OF SILICON HERE ON EARTH?
Bernstein — There have been ideas about minerals holding information just as DNA holds information. DNA holds information in a chain that is read from one end to the other. In contrast, a mineral could hold information in two dimensions [on its surface]. A crystal grows when new atoms arrive on the surface, building layer upon layer. So, if a crystal sheet cleaved off and then started to grow that would be like the birth of a new organism and would carry information from generation to generation. But is a replicating crystal alive? To date, I don’t think that there is actually any evidence that minerals pass information like this.
Dorminey — IS THE CRUX OF THE PROBLEM THAT SILICON-BASED LIFE WOULD BE SO SLOWLY REPLICATING THAT IT COULD NEVER MAKE IT IN A DYNAMIC UNIVERSE?
Bernstein — I don’t think that any Silicon life form could be a biological threat to us. If they were high tech, they might eat our buildings or shoot guns at us but I don’t see how they could infect us. We run hot and move fast. If we don’t, things will catch us and eat us.
If they are also tougher than we are and whatever feeds on them is also slow and Silicon based maybe being slow doesn’t matter.
Dorminey — WHAT WOULD BE THE SIGNATURES OF SILICON-BASED LIFE?
Bernstein — If they are not technological, they would be very tough to detect. We could look for unstable, unexpected silicon molecules; some high energy molecule that should not be there, or molecular chains of all the same length.
Dorminey — DO YOU THINK THAT SILICON-BASED LIFE MIGHT EXIST SOMEWHERE OUT THERE?
Bernstein — Maybe deep below the surface of a planet in some very hot hydrogen-rich, Oxygen-poor environment, you would have this complex silane chemistry. There, maybe silanes would form reversible silicon bonds with selenium or tellurium.
Dorminey — IF SUCH SILICON-BASED LIFE DID CROP UP, WHAT WOULD BE ITS EVOLUTIONARY ENDGAME?
Bernstein — If it could evolve past the protist [microorganism] stage, then I think it could evolve intelligence. I have no idea how likely it is for intelligence to evolve, but I can believe in silicon crystals passing information from layer to layer or in silicon artificial intelligence, but I don’t expect to see silicon apes playing their equivalent of “Angry Birds” on their Silicon-Phones.
Dorminey — IF SILICON-LIFE DID EVOLVE, WOULD ITS LIFESPAN BE MUCH LONGER THAN ITS CARBON-BASED ANALOGUES?
Bernstein — The replicating mineral that I described earlier would be living very, very slowly on Earth’s surface. But maybe somewhere very much hotter, its lifespan would be shorter. That’s because presumably lifespan is connected to the pace of your chemistry, which depends on temperature.
Dorminey — FINALLY, WHAT WOULD ENDANGER NON-CARBON-BASED LIFE?
Bernstein — Physical harm for sure. Presumably you could take a jackhammer to it?
But our biochemistry would not be pathogens to it; we could not “infect” them as was the case in “War of the Worlds.”
The landing site of Viking 1 on Mars in 1977, with trenches dug in the soil for the biology experiments. Credit: NASA/JPL
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One of the most controversial and long-debated aspects of Mars exploration has been the results of the Viking landers’ life-detection experiments back in the 1970s. While the preliminary findings were consistent with the presence of bacteria (or something similar) in the soil samples, the lack of organics found by other instruments forced most scientists to conclude that the life-like responses were most likely the result of unknown chemical reactions, not life. Gilbert V. Levin, however, one of the primary scientists involved with the Viking experiments, has continued to maintain that the Viking landers did indeed find life in the Martian soil. He also now thinks that the just-launched Curiosity rover might be able to confirm this when it lands on Mars next summer.
Curiosity is not specifically a life-detection mission. Rather, it continues the search for evidence of habitability, both now and in the past. But is it possible that it could find evidence for life anyway? Levin believes it could, between its organics detection capability and its high-resolution cameras.
The major argument against the life-detection claims was the lack of organics found in the soil. How could there be life with no organic building blocks? It has since been thought that any organics were destroyed by the harsh ultraviolet radiation or other chemical compounds in the soil itself. Perchlorates could do that, and were later found in the soil by the Phoenix mission a few years ago, closer to the north pole of Mars. The experiments themselves, which included baking the soil at high heat, may have destroyed any organics present (part of the studies involved heating the soil to kill any organisms and then study the residual gases released as a result, as well as feeding nutrients to any putative organisms and analyzing the gases released from the soil). If Curiosity can find organics, either in the soil or by drilling into rocks, Levin argues, that would bolster the case for life being found in the original Viking experiments, as they were the “missing piece” to the puzzle.
So what about the cameras? Any life would have to be macro, of visible size, to be detected. Levin and his team had also found “greenish coloured patches” on some of the nearby rocks. (I still have a little booklet published by Levin at the time, “Color and Feature Changes at Mars Viking Lander Site” which describes these in more detail). When as a test, lichen-bearing rocks on Earth were viewed with the same camera system using visible and infrared spectral analysis, the results were remarkably similar to what was seen on Mars. Again, since then though, those results have been widely disputed, with most scientists thinking the patches were mineral coatings similar to others seen since then. Of course, there is also the microscopic imager, similar to that on the Spirit and Opportunity rovers, although microorganisms would still be too small to be seen directly.
Regardless, Levin feels that Curiosity just might be able to vindicate his earlier findings, stating “This is a very exciting time, something for which I have been waiting for years. At the very least, the Curiosity results may bring about my long-requested re-evaluation of the Viking LR results. The Viking LR life detection data are the only data that will ever be available from a pristine Mars. They are priceless, and should be thoroughly studied.”
It was also announced that Kepler has found 1,094 more planetary candidates, increasing the number now to 2,326! That’s an increase of 89% since the last update this past February. Of these, 207 are near Earth size, 680 are super-Earth size, 1,181 are Neptune size, 203 are Jupiter size and 55 are larger than Jupiter. These findings continue the observational trend seen before, where smaller planets are apparently more numerous than larger gas giant planets. The number of Earth size candidates has increased by more than 200 percent and the number of super-Earth size candidates has increased by 140 percent.
