What is Consuming Hydrogen and Acetylene on Titan / 06.03.10

Two new papers based on data from NASA’s Cassini spacecraft scrutinize the complex chemical activity on the surface of Saturn’s moon Titan. While non-biological chemistry offers one possible explanation, some scientists believe these chemical signatures bolster the argument for a primitive, exotic form of life or precursor to life on Titan’s surface. According to one theory put forth by astrobiologists, the signatures fulfill two important conditions necessary for a hypothesized “methane-based life.” One key finding comes from a paper online now in the journal Icarus that shows hydrogen molecules flowing down through Titan’s atmosphere and disappearing at the surface. Another paper online now in the Journal of Geophysical Research maps hydrocarbons on the Titan surface and finds a lack of acetylene.

This lack of acetylene is important because that chemical would likely be the best energy source for a methane-based life on Titan, said Chris McKay, an astrobiologist at NASA Ames Research Center, Moffett Field, Calif., who proposed a set of conditions necessary for this kind of methane-based life on Titan in 2005. One interpretation of the acetylene data is that the hydrocarbon is being consumed as food. But McKay said the flow of hydrogen is even more critical because all of their proposed mechanisms involved the consumption of hydrogen. “We suggested hydrogen consumption because it’s the obvious gas for life to consume on Titan, similar to the way we consume oxygen on Earth,” McKay said. “If these signs do turn out to be a sign of life, it would be doubly exciting because it would represent a second form of life independent from water-based life on Earth.”

To date, methane-based life forms are only hypothetical. Scientists have not yet detected this form of life anywhere, though there are liquid-water-based microbes on Earth that thrive on methane or produce it as a waste product. On Titan, where temperatures are around 90 Kelvin (minus 290 degrees Fahrenheit), a methane-based organism would have to use a substance that is liquid as its medium for living processes, but not water itself. Water is frozen solid on Titan’s surface and much too cold to support life as we know it. The list of liquid candidates is very short: liquid methane and related molecules like ethane. While liquid water is widely regarded as necessary for life, there has been extensive speculation published in the scientific literature that this is not a strict requirement.

The new hydrogen findings are consistent with conditions that could produce an exotic, methane-based life form, but do not definitively prove its existence, said Darrell Strobel, a Cassini interdisciplinary scientist based at Johns Hopkins University in Baltimore, Md., who authored the paper on hydrogen. Strobel, who studies the upper atmospheres of Saturn and Titan, analyzed data from Cassini’s composite infrared spectrometer and ion and neutral mass spectrometer in his new paper. The paper describes densities of hydrogen in different parts of the atmosphere and the surface. Previous models had predicted that hydrogen molecules, a byproduct of ultraviolet sunlight breaking apart acetylene and methane molecules in the upper atmosphere, should be distributed fairly evenly throughout the atmospheric layers.

imagery from Galileo showing emission of gases

Strobel found a disparity in the hydrogen densities that lead to a flow down to the surface at a rate of about 10,000 trillion trillion hydrogen molecules per second. This is about the same rate at which the molecules escape out of the upper atmosphere. “It’s as if you have a hose and you’re squirting hydrogen onto the ground, but it’s disappearing,” Strobel said. “I didn’t expect this result, because molecular hydrogen is extremely chemically inert in the atmosphere, very light and buoyant. It should ‘float’ to the top of the atmosphere and escape.”

Strobel said it is not likely that hydrogen is being stored in a cave or underground space on Titan. The Titan surface is also so cold that a chemical process that involved a catalyst would be needed to convert hydrogen molecules and acetylene back to methane, even though overall there would be a net release of energy. The energy barrier could be overcome if there were an unknown mineral acting as the catalyst on Titan’s surface. The hydrocarbon mapping research, led by Roger Clark, a Cassini team scientist based at the U.S. Geological Survey in Denver, examines data from Cassini’s visual and infrared mapping spectrometer. Scientists had expected the sun’s interactions with chemicals in the atmosphere to produce acetylene that falls down to coat the Titan surface. But Cassini detected no acetylene on the surface.

In addition Cassini’s spectrometer detected an absence of water ice on the Titan surface, but loads of benzene and another material, which appears to be an organic compound that scientists have not yet been able to identify. The findings lead scientists to believe that the organic compounds are shellacking over the water ice that makes up Titan’s bedrock with a film of hydrocarbons at least a few millimeters to centimeters thick, but possibly much deeper in some places. The ice remains covered up even as liquid methane and ethane flow all over Titan’s surface and fill up lakes and seas much as liquid water does on Earth. “Titan’s atmospheric chemistry is cranking out organic compounds that rain down on the surface so fast that even as streams of liquid methane and ethane at the surface wash the organics off, the ice gets quickly covered again,” Clark said. “All that implies Titan is a dynamic place where organic chemistry is happening now.”

The absence of detectable acetylene on the Titan surface can very well have a non-biological explanation, said Mark Allen, principal investigator with the NASA Astrobiology Institute Titan team. Allen is based at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. Allen said one possibility is that sunlight or cosmic rays are transforming the acetylene in icy aerosols in the atmosphere into more complex molecules that would fall to the ground with no acetylene signature. “Scientific conservatism suggests that a biological explanation should be the last choice after all non-biological explanations are addressed,” Allen said. “We have a lot of work to do to rule out possible non-biological explanations. It is more likely that a chemical process, without biology, can explain these results – for example, reactions involving mineral catalysts.”

“These new results are surprising and exciting,” said Linda Spilker, Cassini project scientist at JPL. “Cassini has many more flybys of Titan that might help us sort out just what is happening at the surface.” The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL.

For more information about the Cassini-Huygens mission visit and

Jia-Rui Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.

Cathy Weselby 650-604-2791
NASA Ames Research Center, Moffett Field, Calif.

Life on Saturn’s Titan: Could It be Methane Based?
by Casey Kazan / March 20, 2010

Saturn’s giant moon Titan has water frozen as hard as granite and Great Lakes-sized bodies of fed by a complete liquid cycle, much like the hydrological cycle on Earth, but made up of methane and ethane rather than on water. Methane and ethane, the simplest hydrocarbon molecules, can assemble themselves into fantastically complex structures. Since complex hydrocarbons form the basis of life on Earth, scientists are wondering if hydrocarbon chemistry on Titan could have crossed the chasm from inanimate matter to some form of life? Titan has been considered a “unique world in the solar system” since 1908 when, the Spanish astronomer, José Comas y Solá, discovered that it had an atmosphere, something non-existent on other moons. It seems perfectly appropriate that one of the prime candidates for life in our solar system, Saturn’s largest moon, should have surface lakes, lightning, shorelines, relatively thick nitrogen atmosphere -and seasons. Titan can be viewed as an early-model Earth. And 100% of all known Earths have awesome life on them. The significantly lower temperature is a bit of a stumbling block (it’s ten times as far from the sun as us), but there’s a strong possibility of subterranean microbial life – or even a prebiotic “Life could happen!” environment. If a space traveler ever visits Titan, they will find a world where temperatures plunge to minus 274 degrees Fahrenheit, methane rains from the sky and dunes of ice or tar cover the planet’s most arid regions -a cold mirror image of Earth’s tropical climate, according to scientists at the University of Chicago.

Titan’s ice is stronger than most bedrock found on earth, yet it is more brittle, causing it to erode more easily, according to new research by San Francisco State University Assistant Professor Leonard Sklar. Sklar and his team developed new measurements from tests on ice as cold as minus 170 degrees Celcius which demonstrate that ice gets stronger as temperature decreases. Understanding ice and its resistance to erosion is critical to answering how Titan’s earth-like landscape formed. Titan has lakes, rivers and dunes, but its bedrock is made of ice as cold as minus 180 degrees Celcius, eroded by rivers of liquid methane. “You have all these things that are analogous to Earth. At the same time, it’s foreign and unfamiliar,” said Ray Pierrehumbert, the Louis Block Professor in Geophysical Sciences at Chicago. Titan, one of Saturn’s 60 moons, is the only moon in the solar system large enough to support an atmosphere. Pierrehumbert and colleague Jonathan Mitchell, have been comparing observations of Titan collected by the Cassini space probe and the Hubble Space Telescope with their own computer simulations of the moon’s atmosphere. “One of the things that attracts me about Titan is that it has a lot of the same circulation features as Earth, but done with completely different substances that work at different temperatures,” Pierrehumbert said. On Earth, for example, water forms liquid and is relatively active as a vapor in the atmosphere. But on Titan, water is a rock. “It’s not more volatile on Titan than sand is on Earth.”

Methane-natural gas-assumes an Earth-like role of water on Titan. It exists in enough abundance to condense into rain and form puddles on the surface within the range of temperatures that occur on Titan. “The ironic thing on Titan is that although it’s much colder than Earth, it actually acts like a super-hot Earth rather than a snowball Earth, because at Titan temperatures, methane is more volatile than water vapor is at Earth temperatures,” Pierrehumbert said. Pierrehumbert and Mitchell even go so far as to call Titan’s climate tropical, even though it sounds odd for a moon that orbits Saturn more than nine times farther from the sun than Earth. Along with the behavior of methane, Titan’s slow rotation rate also contributes to its tropical nature. Earth’s tropical weather systems extend only to plus or minus 30 degrees of latitude from the equator. But on Titan, which rotates only once every 16 days, “the tropical weather system extends to the entire planet,” Pierrehumbert said.

Titan’s dense, nitrogen-methane atmosphere responds much more slowly than Earth’s atmosphere, as it receives about 100 times less sunlight than Earth. Seasons on Titan last more than seven Earth years. Its clouds form and move much like those on Earth, but in a much slower, more lingering fashion. Physicists from the University of Granada and University of Valencia, analyzing data sent by the Cassini-Huygens probe from Titan, have “unequivocally” proved that there is natural electrical activity on Titan. The world scientist community believes that the probability of organic molecules, precursors of life, being formed is higher on planets or moons which have an atmosphere with electrical storms.

Scientists with NASA’s Cassini mission have monitored Titan’s atmosphere for three-and-a-half years, between July 2004 and December 2007, and observed more than 200 clouds. They found that the way these clouds are distributed around Titan matches scientists’ global circulation models. The only exception is timing — clouds are still noticeable in the southern hemisphere while fall is approaching. “Titan’s clouds don’t move with the seasons exactly as we expected,” said Sebastien Rodriguez of the University of Paris Diderot, in collaboration with Cassini visual and infrared mapping spectrometer team members at the University of Nantes, France. “We see lots of clouds during the summer in the southern hemisphere, and this summer weather seems to last into the early fall. It looks like Indian summer on Earth, even if the mechanisms are radically different on Titan from those on Earth. Titan may then experience a warmer and wetter early autumn than forecasted by the models.”

On Earth, abnormally warm, dry weather periods in late autumn occur when low-pressure systems are blocked in the winter hemisphere. By contrast, scientists think the sluggishness of temperature changes at the surface and low atmosphere on Titan may be responsible for its unexpected warm and wet, hence cloudy, late summer. Scientists will continue to observe the long-term changes during Cassini’s extended mission, which runs until the fall of 2010, which will offer plenty of opportunities to monitor climate change on Titan — the spacecraft makes its next flyby of the moon on June 6. We’ll learn if the sluggish weather is the result of a slow rate of temperature change at the surface.

Cassini results so far don’t show if Titan has an ocean beneath the surface, but scientists say this hypothesis is very plausible and they intend to keep investigating. Detecting tides induced by Saturn, a goal of the radio science team, would provide the clearest evidence for such a hidden water layer. “Additional flybys may tell us whether the crust is thick or thin todaf,” says Jonathan Lunine, a Cassini interdisciplinary investigator with the University of Rome, Tor Vergata, Italy, and the University of Arizona, Tucson. “With that information we may have a better understanding of how methane, the ephemeral working fluid of Titan’s rivers, lakes and clouds, has been resupplied over geologic time. Like the history of water on Earth, this is fundamental to a deep picture of the nature of Titan through time.”

{The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency.}

The team found two types of bacteria living in Lost Hammer that feed off the methane and likely breathe sulfate.

Bacteria Suited for Life on Mars Discovered / June 9, 2010

Researchers in Canada and the United States have discovered that methane-eating bacteria survive in a unique spring located on Axel Heiberg Island in Northern Canada. Because the environment there is similar to possible past or present springs on Mars, scientists surmise that the “Red Planet” might also be able to support a form of life. Canadian and U.S. scientists say they’ve concluded life might survive on Mars since they’ve found evidence of bacteria in a martian-like environment on Earth. Researchers at Canada’s McGill University, the University of Toronto, the National Research Council of Canada and the SETI Institute in the United States say they have discovered methane-eating bacteria survive in a unique spring located on Axel Heiberg Island in Northern Canada. Lyle Whyte, a McGill microbiologist, said the Lost Hammer Spring supports microbial life — and the spring’s environment is similar to possible past or present springs on Mars. That, he said, means the “Red Planet” might also support a form of life. The Canadian spring’s sub-zero water is so salty it doesn’t freeze and it has no consumable oxygen in it. There are, however, big bubbles of methane that come to the surface, which had provoked the researchers’ curiosity as to whether the gas was being produced geologically or biologically and whether anything could survive in such an extreme hypersaline sub-zero environment. “We were surprised that we did not find methanogenic bacteria that produce methane at Lost Hammer,” Whyte said. “But we did find other very unique anaerobic organisms — organisms that survive by essentially eating methane and probably breathing sulfate instead of oxygen.”

{The research appeared in the International Society for Microbial Ecology Journal.}

Titan’s atmosphere oddity consistent with methane-based life
by John Timmer / June 4, 2010

Something strange is afoot in the atmosphere of Saturn’s moon Titan, according to data sent back from the Cassini mission. Data returned from a spectrometer on Cassini indicates that there’s a large flux of hydrogen in the moon’s atmosphere, with the gas forming in the upper atmosphere and being removed from the atmosphere at Titan’s surface. We don’t currently know what process is ensuring its removal, but the amounts of hydrogen being taken out of the atmosphere are consistent with an earlier proposal of methane-based life.

Titan’s atmosphere is rich in hydrocarbon compounds, and chemical changes in the upper atmosphere are driven by the arrival of ultraviolet light from the sun. One of the expected results of the UV exposure is the liberation of molecular hydrogen from methane via a process that produces more complex hydrocarbons. With little oxygen to react with, the molecular hydrogen should remain stable. Some of it will escape into space, but a new paper indicates that a substantial amount of that hydrogen migrates down through the atmosphere towards Titan’s surface. Since it’s not accumulating there, some chemical process must be removing it from the atmosphere; right now, we don’t know what that process is, and, as NASA’s own news piece on the topic notes, the first option for scientists is to consider simple chemistry.

However, the abstract of the paper notes that this level of hydrogen consumption is consistent with an earlier prediction of methanogenic life. In short, the life would get its energy by “burning” the hydrogen with a carbon source instead of oxygen, releasing methane (CH4) in the process. The source of the carbon is where a second paper (not yet online) comes in. Models of Titan’s upper atmosphere suggest that significant amounts of acetylene should be produced by the reactions there, and this would provide an excellent source of carbon to any hypothetical metabolisms. The surprise of the second paper is that there’s very little acetylene to be found on Titan’s surface. Two chemical enigmas certainly don’t constitute life, and the authors of the latter paper provide a variety of ways to account for the acetylene shortage that don’t involve an organism. It’s also important to remember that there won’t be anything resembling liquid water on the surface of Titan, so anything alive there would have to be living in a methane/ethane soup (not to mention at temperatures nearing -200°C).

Scientists are a cautious bunch, and it’s likely that these results will remain in limbo for a while. The discovery of plumes of methane in the atmosphere of Mars was another chemical enigma that might be evidence for life. It’s been about a year and a half since their announcement and nobody has come up with a satisfying explanation for their presence (at least as far as I’m aware), but the scientific community is nowhere close to ready to call that conclusive evidence for life.

Icarus, 2010. DOI: 10.1016/j.icarus.2010.03.003
Journal of Geophysical Research Atmospheres, 2010.10.1029/2009JE003369.

Mars makes methane: sign of life or geology at work?
by John Timmer / January 15, 2009

The more we look at the surface of the Red Planet, the more interesting things we’re finding there. The latest results haven’t even required a trip to Mars. Instead, a series of spectroscopy readings from telescopes in Hawaii have tracked changes in the composition of Mars’ atmosphere over time. To the researchers’ surprise, the Martian summer triggered large releases of methane into the atmosphere from three distinct regions on the planet. Right now, the researchers say they don’t have sufficient data to determine if the source of the methane is biological or geological.

The data themselves are being reported in a paper that is being released by Science today, and NASA hosted a press conference to describe them. The basic technique involved using a spectrometer hooked up to one of the large Hawaiian telescopes (over the span of several years of observations, they used several individual telescopes). They took samples from multiple pixels along the north-south axis to get one dimension of spatial resolution; the rotation of the planet itself provided a second. Absorption peaks from the gasses in the earth’s atmosphere were subtracted, leaving the signal from Mars’ atmosphere behind.

During the winter, the area of the spectrum that includes a signal of methane was basically a blank. But, as Martian summer arrived in the northern hemisphere, three distinct areas of the planet started showing signs of methane production. Eventually, three distinct atmospheric plumes appeared, representing a total of 19,000 metric tons of methane; the research suggests a production rate of over a half-kilogram of a second at its peak, a rate comparable to that of hydrocarbon seeps on earth.

As might be inferred from the low levels present in the winter, Mars doesn’t provide a hospitable environment for methane. The researchers estimate that, should this be a one-time only event, the methane that’s released would have a half life of four years; if this is an annual event, it must last less than a year. Given the oxidants found by the Mars Phoenix Lander and the dust storms that sweep that material into the sky on a regular basis, the authors suggest that it probably shouldn’t be viewed as a surprise that the methane doesn’t last.

So, where is it coming from? At the press conference, the NASA scientists noted that no plumes came from the area that’s normally covered by an ice cap during the Martian winter, so it’s not simply a matter of the source being blocked for part of the year. The areas where it does come from are within regions of the planet that have been found to have had liquid water in the past. Beyond that, however, the three plume sources seem to have little in common. The authors note that Terra Sabae has sub-surface hydrogen, Nili Fossae has hydrated minerals, and Syrtis Major has a volatile-rich substrate. Of course, it’s possible that there are small regions within these areas that do share some geochemistry. Mars is now tectonically dead, and the lack of sulfur dioxide suggests that the gas is not coming from any volcanic activity. Still, there is no way to rule out that some hot mantle material hasn’t come into contact with the regions’ residual water, which could create a steam reaction with minerals that could liberate water. On earth, however, these sorts of faults tend to create notable surface features, and cool fairly rapidly.

The alternative that springs to everyone’s mind is a biological source. The finding that bacteria can live at the bottom of South African mines provides a model cited by the authors. Radioactive activity could break apart water and release hydrogen, which the bacteria react with carbon dioxide to release energy, with methane as a byproduct. The problem for either of these cases is that the production of methane would be occurring several kilometers down in the crust, so it’s nothing that would be accessible to machinery NASA plans to send to Mars any time soon. Biological activity tends to involve lighter isotopes of elements, so it’s possible that mass spectroscopy of the methane might provide a clue, but getting a concentrated sample would be very difficult. It came out during the press call that one of the regions was a potential site for the Mars Science Lab that was eliminated late in the planning stages; since that mission has now been delayed until 2011, there’s a chance that decision will be revisited.

Although there’s no good way to distinguish among the possible sources, the finding is a clear indication that Mars remains an active planet, and liquid water is almost certainly associated with that activity. As Martian years take two on earth, scientists will be anxiously waiting to see whether the plumes return next Martian summer, an event that would rule out some of the more unlikely sources. In the mean time, the discovery will almost certainly inspire a lot of scientists to start thinking about a variety of chemical processes that could produce methane, and trying to determine ways to test whether any of those are operating on the red planet.

In the deep, a community of one
by John Timmer / October 9, 2008

As researchers probed a varity of environments that were once thought to be inhospitable to life, they were surprised to find large bacterial communities thriving in places like near-boiling hot springs and volcanic vents deep in the ocean. Faced with this evidence, it was fair to wonder just where the outer edges of survival might be. We may have a hint of that from samples taken from deep in South African mines, which show that life can make it nearly three kilometers down, but it’s far from the thriving communities we find in other extreme environments. In fact, it looks like the bacterial “community” in the mine may be comprised of a single species.

The authors of a paper describing the organism, to be published today in Science, can’t rule out the possibility that there are other microorganisms down in the mine, but their approach seems to make the possibility very unlikely. To start with, they filtered a total of 5,600 liters of mine water to get their sample, which gave other microbes plenty of opportunities to make themselves known. Of the DNA sequences obtained from this sample, over 99.9 percent were from this single species; over half of the remainder were obvious contaminants from their own lab. If anything else is there, it’s a small minority of the life present.

The bacteria, which goes by the name Candidatus Desulforudis audaxviator, is pretty homogeneous itself. Of 2.3 million bases present in the genome, all but 32 appeared to be identical in all of the population of bacteria that was sequenced. That’s a lower rate than the human population, and all the more striking given the amount of time that DNA has to pick up mutations; estimates of the nutrient availability (generated primarily from the energy given off during radioactive decay) indicate that it may take 100 to 1,000 years for a cell to divide.

With no other organisms present to engage in symbiosis with, the bacteria carry genes to do everything they need. They can make all the amino acids, extract useful carbon from carbon monoxide, and either fix nitrogen or obtain it from ammonia in the water. Oxygen is scarce in the environment, and the organism doesn’t appear to make any proteins that could possibly protect them from it. To run its metabolism, it reduces SO4. If it runs short of any of these, it has a flagella and chemosensory proteins that help it move off in search of more.

Extreme environments tend to be inhabited by archaea, so this bacteria is somewhat an exception to the rule. But the authors note that many of the key genes that enable it to survive in the hostile deeps of the mine actually originated in archaea, but were picked up by horizontal gene transfer. In this sense, it’s more of an exception that proves the rule. The fact that this organism requires such a diverse array of capabilities simply to survive, and is the only thing that manages to do so, suggests that this environment represents one of the outer edges of survivability for terrestrial life.

Extreme bugs back idea of life on Mars
by Kelly Young and David L Chandler / 07 December 2005

Methane-producing microbes have been discovered in two extreme environments on Earth – buried under kilometres of ice in Greenland and living in hot, dry desert soil. The findings lend weight to the idea that similar organisms may have lived on Mars. Live microbes making methane were found in a glacial ice core sample retrieved from three kilometres under Greenland by researchers from the University of California, Berkeley, US. It is the first time such archaea have been found at that depth, says Buford Price, one of the research team, which published its results in the Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0507601102).

Scientists had already noticed that the concentrations of methane in the lowest 90 metres of the ice core was 10 times as high as that at other depths. Now the Berkeley scientists have found the likely cause – correspondingly higher levels of microbes that produce methane, known as methanogens. Areas of high methane concentration in the Martian atmosphere have been spotted by Europe’s Mars Express spacecraft, but its origin is uncertain. A renewable source of methane would be needed, as otherwise ultraviolet light from the Sun would have destroyed it within 340 years. The methane could come from a geological source, such as unseen volcanic activity, or biological sources such as methanogens.

Poor-man’s borehole
Price’s group used the data from Greenland to devise a scenario on Mars, in order to guide future missions. The methanogens in the ice cores existed at -10°C, but could produce more methane in warmer conditions. In order to account for the methane seen on Mars, they calculated the bugs would have to live at 0°C or above. This temperature is likely to occur between 150 metres and 8 kilometres beneath the Martian surface, depending on the rock type. It would then take between 15 years and 30,000 years for that methane to percolate up to the surface. “In my opinion, there’s no way in my lifetime that NASA will find a way of drilling a borehole 150 metres deep [on Mars],” Price told New Scientist. “But the poor-man’s borehole is just looking at what’s been thrown out of a crater.” So a spacecraft could be sent to a large crater where higher levels of atmospheric methane have been detected. The lander could then drill a shorter distance down into the crater to try to find evidence of life.

Desert dwellers
Another new study, reported in the journal Icarus (vol 178, p 277), has also discovered methanogens in a harsh environment on Earth. Researchers studied dozens of soil and vapour samples from five different desert environments in Utah, Idaho and California in the US, and in Canada and Chile. Of these, five soil samples and three vapour samples from the vicinity of the Mars Desert Research Station in Utah were found to have signs of viable methanogens. The methane in the vapour samples was 300 times higher than background levels. One of the team, Timothy Kral of the University of Arkansas, US, told New Scientist that dry conditions usually kill this type of microbe: “So finding them in a dry place is not what everyone would have expected.”

Methanogens require anaerobic (oxygen-free) environments to survive, and most combine carbon dioxide and hydrogen to generate energy. Kral explains that their samples were collected from possible anaerobic settings such as dry-channel deposits 70 centimetres underground. The surface of Mars is also very dry, so the finding helps support the idea that the methane detected there could be an indicator of current microbial activity. The lesson for Mars, says Andrew Knoll, a biogeochemist at Harvard University, US, and a member of the Mars rover science team, is that methanogenesis may be possible there, but only when the right conditions of a limited-oxygen environment and availability of nutrients occur.

A whiff of life on the Red Planet
by Jenny Hogan / 16 February 2005

A leading European Space Agency scientist says he has found a gas in the Martian atmosphere that he believes can only be explained by the presence of life. But the few researchers who have been privy to the facts say that such a conclusion is premature. Vittorio Formisano of the Institute of Physics and Interplanetary Science in Rome will be speaking next week at the first conference dedicated to the results from ESA’s Mars Express spacecraft. The craft has been orbiting the Red Planet since December 2003. Agustin Chicarro, the project scientist for Mars Express and the organiser of the conference in Noordwijk, the Netherlands, says he expects sparks to fly. “We have allocated one full hour of debate – it could be a lively discussion.”

Scientists are understandably cautious. The list of discredited claims for life on Mars is long: from canals built by intelligent beings that early astronomers thought they saw, to “bacteria fossils” found in a Martian meteorite that fell in Antarctica. The fossil-like structures, which were discovered in 1996, are now thought to have been etched by chemical processes. The debate reignited last year when three teams, including one led by Formisano, independently detected methane on Mars – a gas that bacteria produce on Earth. Some speculated that similar microbes could be producing the methane on Mars. But others argued that methane at the observed concentrations could be explained by non-biological processes producing about 150 tonnes of methane per year. A comet that crashed on Mars long ago or some kind of volcanic activity could supply that amount.

Soil-based life
Now Formisano is saying that there is much more methane on Mars. He bases this on the detection of a different gas, formaldehyde, by the Planetary Fourier Spectrometer (PFS), an instrument on Mars Express that he runs. Formisano averaged thousands of measurements taken by the PFS and calculated that the Martian atmosphere has formaldehyde in concentrations of 130 parts per billion. He thinks that the gas is being produced by the oxidation of methane and estimates that 2.5 million tonnes of methane per year are needed to produce it. “I believe that until it is demonstrated that non-biological processes can produce this, possibly the only way to produce so much methane is life,” he says. “My conclusion is there must be life in the soil of Mars.”

The presence of formaldehyde could explain why earlier studies found uneven distributions of methane on Mars, says Formisano. Because methane takes hundreds of years to break down by itself, the wind should even out the concentration of the gas around the planet. But if it is being oxidised in some regions, such as those that are rich in iron compounds, then you would find less methane in those areas. But other experts, including Formisano’s collaborators on the PFS and other principal investigators on the Mars Express mission to whom Formisano has presented his work, advise caution. He may be alone in pursuing formaldehyde, says one of his collaborators, Sushil Atreya from the University of Michigan, Ann Arbor, US.

Pushed to the limit
Others warn that Formisano is pushing the instrument to its limit in trying to look for formaldehyde. To identify compounds, the PFS looks for dark absorption lines in the spectrum of light reflected from Mars. Formaldehyde absorbs a handful of infrared wavelengths, but the instrument is not sensitive enough to see the individual lines. “It is not 100% convincing,” says Therese Encrenaz, from the Paris Observatory, France, another of Formisano’s colleagues. “But I think it deserves further work.”

Even if Formisano has found formaldehyde, it is not necessarily coming from the oxidation of methane. And even if there are large amounts of methane on the Red Planet, it might not be biological in origin. “Frankly, we don’t know what the internal geology of Mars is like. To draw conclusions on whether it is biological or not at this stage is damn risky,” says Michael Mumma of NASA’s Goddard Space Flight Centre in Greenbelt, Maryland, US, who last year found methane on Mars using Earth-based telescopes.

Formisano agrees that he has no conclusive proof. “I cannot demonstrate for sure,” he says. “But these hints for life I have found are the best one can get. The next step is to go there and look for it.” Future missions, such as NASA’s Mars Science Laboratory now in the planning stage, will look for and analyse organic molecules in the soil. While other evidence suggests that Mars was and may still be hospitable to life, ESA is playing it safe. “If this issue was a bit less controversial, then maybe we would be at the point of having some kind of press conference,” says Chicarro. “But we need to leave the scientific community to its natural course and have it debated there.” Debate at next week’s conference is certain.

Crater Critters: Where Mars Microbes Might Lurk
by Robert Roy Britt / 20 December 2005

The more scientists have learned about Mars in recent years, the more some believe that finding life might involve a deep drilling project. With the surface of the red planet desolate and mostly dry, one consistently appealing idea has been that pockets of underground water might harbor microbes. The problem is, studies have suggested reaching the pockets might require drilling a thousand feet (hundreds of meters) below the surface. P. Buford Price, a physics professor at the University of California, Berkeley, has an idea for another place to look. If there is any life in the belly of Mars, some of it might be found around meteor craters, where rock has been tossed up from deep down.

The idea fits with recent suggestions by European scientists that pockets of methane in Martian air could be signs of life below. Methane should not last more than 300 years in the atmosphere, so the concentrations of it suggest a source that might be biological, the Europeans reason. On Earth, even in solid rock 660 feet (200 meters) below the surface, methanogens have been found to thrive. Methanogens are ancient relatives of bacteria that take in hydrogen and carbon dioxide and emit methane. Price and his colleagues have found that the same creatures deep in Antarctic ice emit enough methane to affect concentrations of the gas detected in drilling projects. Methane pockets in ice cores taken from Greenland registered levels of the gas that in spots were 10 times higher than expected. “We found methanogens at precisely those depths where excess methane had been found, and nowhere else,” Price said.

Craters already dug
While Earth and Mars are very different places, and no one knows whether the source of the methane on Mars has anything to do with life (it could be geologic in nature) Price figures the whole thing can be tested out without the need to drill too far down. Under Antarctic ice, his team was able to detect concentrations of methanogens as low as 16 per cubic inch. “Detecting this concentration of microbes is within the ability of state-of-the-art instruments, if they could be flown to Mars and if the lander could drop down at a place where Mars orbiters have found the methane concentration highest,” Price said. “There are oodles of craters on Mars from meteorites and small asteroids colliding with Mars and churning up material from a suitable depth, so if you looked around the rim of a crater and scooped up some dirt, you might find them if you land where the methane oozing out of the interior is highest.” The idea was published online earlier this month by the journal Proceedings of the National Academy of Sciences.

Bizarre Creature in Idaho Raises Prospects for Life on Mars
By Robert Roy Britt / 16 January 2002

They eat hydrogen, breathe carbon dioxide, and belch methane. And they form the root of an ecosystem unlike any previously known on Earth. Meet the methanogen, a tiny organism living in complete darkness 660 feet (200 meters) underneath the surface of Idaho. Researchers report in the Jan. 17 issue of the journal Nature the discovery of a community of various organisms dominated and supported by these methanogens, creatures they say could represent just the sort of life to look for when turning over rocks on Mars. The work, along with another report this week of life found in extreme conditions in Antarctica, adds to mounting evidence for life’s tenacity and creativity, fueling increased speculation about the prospects for life on other worlds.

Extreme diet
Unlike other organisms at the bottom of the food chain, methanogens need little of the traditional sustenance that biologists associate with life. They get by without oxygen and no help from sunlight, said the U.S. Geological Survey’s Francis H. Chapelle, who led the study along with Derek Lovley of the University of Massachusetts. Methanogens simply feed off hydrogen in the rocks around an underground hot spring. No one knew if life could live in such conditions. So the Idaho site was chosen for its lack of organic matter, stuff that is originally produced by sunlight-powered organisms and is known to support other subsurface ecosystems. “This kind of microbial community has never been found on Earth,” Chapelle told, adding that it “may be representative of the kinds of life that initially evolved on the early Earth, and which may presently occur on Mars or Europa.”

Methanogens belong to an ancient group related to bacteria, called the archaea. All archaea are outfitted for survival in extreme environments. They are thought to have dominated primitive Earth, when oxygen was a rare commodity. Idaho is not the only home to methanogens. They cause gas in the digestive tracts of humans. And they’re found in oxygen-deprived mud at the bottom of swamps. But they are not seen as essential to supporting other life in these environments, as is the case in Idaho.

Life as we know it
Places considered most likely to harbor extraterrestrial life — pockets of underground water on Mars or an ocean under the frozen crust of Jupiter’s moon Europa — are only presumed to exist, and since they exist below the surface and get no sunlight, any life there would have to have an alternative means of fuel. The new finding shows that the recipe for life is simpler than previously thought, that sunlight is not needed, and that improves the prospects for finding ET, researchers said. “Hydrogen may well be an important requirement for extraterrestrial life,” Chapelle said.

And hydrogen is everywhere. It’s the most abundant element in the universe. Importantly, preliminary data recently sent back by the Mars Odyssey spacecraft suggests there may be a wealth of hydrogen within 3 feet (1 meter) of the surface of Mars, just south of the permanently frozen north polar region. Other studies have shown Mars and Europa might both contain suitable hydrogen-rich environments. “If hydrogen is indeed present on Mars in association with liquid water, the kind of metabolism we describe … may occur on Mars,” Chapelle said. William B. Whitman, a University of Georgia microbiologists who was not involved in the new study, said methanogens were hypothesized to exist in environments like the one studied in Idaho, but that it was unusual that they dominate the community of microbes within which they live. “This community composition has not been described before,” Whitman said. And what does it say about life as we know it? “It certainly strengthens the rationale for looking in more kinds of places, especially the subsurface of some of the other planets,” Whitman said.

Wild life
The methanogen discovery is one in a long string of findings over the past two decades showing how resilient and creative life can be. Researchers have found simple organisms in relatively dry valleys of Antarctica, in pockets of water under permanent packs of ice, deep inside Earth and huddled around hydrothermal vents at pitch-black ocean bottoms. Growing knowledge of Mars and recent findings on Earth bolster notions that the Red Planet may be the best place to look for similar extremophiles, as they are called.

Earlier this week, an international team of researchers said they had discovered organisms clinging to life in frigid, salty soil in Antarctica. Average temperatures in the Quartermain Mountains, where the microorganisms were found, are typically less 22 degrees below zero Fahrenheit (-30 C). Less than a half-inch of precipitation falls each year. No place on Earth is more like Mars, the researchers said. The study uncovered fungi and a common bacteria living just below the surface in salt-laden soil, which dramatically lowers the freezing temperature of water by a method not completely understood. The researchers say the same phenomenon may occur on Mars. Other research suggests that soil conditions on parts of Mars could be very similar to the Antarctic dirt. “The glacial climates of Antarctica would have led to glaciers that produced the same kinds of surfaces that were sampled in Antarctica and that we see on Mars today,” said Victor R. Baker of the Lunar and Planetary Lab at the University of Arizona. The Antarctic finding, led by William C. Mahaney of York University in Canada, will be presented in the journal Icarus. Baker and other geologists helped Mahaney interpret the discovery in the context of the potential for life on Mars.

Waiting game
Whether life exists beyond Earth is the greatest question in the minds of many scientists. No other single question channels more funding for space-related scientific research. Yet while the prospects for ET seem to grow with each new discovery on Earth, the plain fact is nobody knows if Mars does or ever did harbor life. Solid evidence could come from robotic probes. NASA alone has several planned over the next decade. Yet many researchers say a human mission to Mars — which is not even in the planning stages at NASA — might be required to literally dig up the necessary evidence. Oxygen-breathing creatures might be wise not to hold their breath for an answer to the ultimate question.

New Life Form Found in Mars-Like Conditions
by Robert Roy Britt / 31 July 2003

Leave it to California to come up with creatures that could be from Mars. Leave it to scientists to make them green. A new species of bacteria has been discovered thriving without oxygen in the harsh waters of northern California’s Mono lake, where conditions perhaps resemble places on the red planet that might support similar life forms, scientists announced Wednesday. A dye used in the laboratory to sort living things from dead stuff rendered the creatures green in an image released by NASA. Under a microscope, the bacteria look like miniature corkscrews winnowing through samples of the highly alkaline water in which they thrive.

There is no solid evidence for life on Mars, so discussion of it is speculative. But on Earth in recent years, researchers have found several species of “extremophiles,” microorganisms that exist in conditions most living things cannot tolerate. The newfound extremophile, called Spirochaeta americana, swims in a high-mineral, salty environment where the pH can reach 10.5, compared to a range of 6.5 to 7.5 that is generally suggested for backyard hot tubs and swimming pools. “The environment these bacteria inhabit would be distinctly inhospitable to many other life forms, including humans,” said Elena Pikuta, a microbiologist at the University of Alabama in Huntsville. Spirochaeta americana joins a growing list of organisms on Earth that don’t mind extreme heat, cold, darkness or other awful conditions. They are ancient life forms that have endured most of what the planet can throw at them. Extremophiles have been found under Antarctic ice, around superhot volcanic vents, eating rock beneath the sea floor munching on hydrogen and belching methane inside Earth’s crust, and even in the waste from nuclear reactors.

Yet fragile
The new species was discovered in a laboratory by analyzing water and mud collected during a single day’s visit to the lake. Outside their native habitat, the hardy creatures turn out to be surprisingly fragile. “These extremely thin and graceful bacteria move with an elegant motion,” Pikuta said. “Their cell walls are very delicate, and it is difficult to keep them alive for long periods in the laboratory.” It is primarily their ability to survive without oxygen that interests astrobiologists, those who study how and whether life might arise beyond Earth. “Since other bodies of the solar system [planets and moons] lack our oxygen-rich atmosphere, microorganisms that thrive without oxygen are good candidates for astrobiology research,” said Richard Hoover, an astrobiologist at NASA’s Marshall Space Flight Center. “If, or when, we find life on other planets, our first discoveries will probably be microorganisms.” Hoover worked with Pikuta on the study, which was published in the May issue of the International Journal of Systematic and Evolutionary Microbiology.

Mono Lake is not like anything known on Mars. But there are is some common ground. Mono is the remnant of a much larger lake whose water level in the Pleistocene era was some 427 feet (130 meters) higher. Some scientists have speculated that depressions seen on Mars might be sites of former lakes. Much of NASA’s Mars program is currently geared toward finding places on the red planet where liquid water might exist. Water is one ingredient needed by all life as we know it. But even if there is liquid water on Mars, that does not guarantee life. “Planets like Mars have conditions that would challenge the existence of highly organized multicellular organisms such as we find on Earth, but that doesn’t mean these harsh places can’t sustain microbial life forms,” Hoover said. “By studying microorganisms found in Earth’s extreme places, like Mono Lake, we can better understand how life might exist on Mars.”

Have We Discovered Evidence For Life On Titan
by Chris McKay / Jun 08, 2010

Recent results from the Cassini mission suggest that hydrogen and acetylene are depleted at the surface of Titan. Both results are still preliminary and the hydrogen loss in particular is the result of a computer calculation, and not a direct measurement. However the findings are interesting for astrobiology.
Heather Smith and I, in a paper published 5 years ago (McKay and Smith, 2005) suggested that methane-based (rather than water-based) life – ie, organisms called methanogens – on Titan could consume hydrogen, acetylene, and ethane. The key conclusion of that paper (last line of the abstract) was “The results of the recent Huygens probe could indicate the presence of such life by anomalous depletions of acetylene and ethane as well as hydrogen at the surface.”

Now there seems to be evidence for all three of these on Titan. Clark et al. (2010, in press in JGR) are reporting depletions of acetylene at the surface. And it has been long appreciated that there is not as much ethane as expected on the surface of Titan. And now Strobel (2010, in press in Icarus) predicts a strong flux of hydrogen into the surface. This is a still a long way from “evidence of life”. However, it is extremely interesting. Benner et al. (2004) first suggested that the liquid hydrocarbons on Titan could be the basis for life, playing the role that water does for life on Earth. Those researchers pointed out that “… in many senses, hydrocarbon solvents are better than water for managing complex organic chemical reactivity”.

Two papers in 2005 followed up on this logic by computing the energy available for methanogenic life based on the consumption of both the organics in Titan’s atmosphere along with the hydrogen in the atmosphere (McKay and Smith, 2005; Schulze-Makuch and Grinspoon, 2005). Both papers made the case that H2 on Titan would play the role that O2 plays on Earth. On Earth organisms (like humans) can react O2 with organic material to derive energy for life’s functions. On Titan organisms could react H2 with organic material to derive energy. The waste product of O2 metabolism on Earth is CO2 and H2O; on Titan the waste product of H2 metabolism would be CH4. As a result of the Cassini mission, there is now abundant evidence for CH4, even in liquid form, on Titan.

Organic molecules on the surface of Titan (such as acetylene, ethane, and solid organics) would release energy if they reacted with hydrogen to form methane. Acetylene gives the most energy. However this reaction will not proceed under ordinary conditions. This is similar to our experience on Earth. Consider a chocolate bar in a jar full of air. The organics in the chocolate would release energy if they reacted with the oxygen in the air but the reaction does not proceed under normal conditions. There are three ways to make it proceed: heat it to high temperatures (fire), expose it to a suitable metal catalyst that promotes the reaction, or eat it and use biological catalysts to cause the reaction. Biology can thrive in an environment that is rich in chemical energy but requires a catalyst for the chemical energy to be released. Such is the case on Titan.

McKay and Smith (2005) predicted that if there were life on Titan living in liquid methane then that life should be widespread on the surface because liquid methane is widespread on the surface. We have direct evidence that the surface of Titan at the landing site of the Huygens Probe near the equator was moist with methane, and radar and near-infrared imagery from Cassini have revealed extensive polar lakes on Titan, both north and south. Methane-based life would have a lot of environments in which to live. Again, this is analogous to Earth. Life is widespread on Earth because it uses water and water is widespread on Earth.

Furthermore, because it is widespread, life on Earth, in turn, has a profound effect on the environment. For example, each spring the amount of CO2 in the atmosphere drops as plants consume it to form leaves; each autumn, the amount of CO2 in the atmosphere goes up as these leaves decompose. That is, because of the ubiquity of life, the Earth breathes: one breath in during the spring, one breath out during the autumn. Widespread life has observable effects. Taking this logic to Titan, McKay and Smith (2005) predicted that Titanian life at the surface would consume near-surface hydrogen and that this might be detectable. The depletion of hydrogen is key because all the chemical methods suggested for life to derive energy from the environment on Titan involve consumption of hydrogen (McKay and Smith 2005; Schulze-Makuch and Grinspoon 2005). Acetylene, ethane, and solid organic material could all be consumed as well. Acetylene yields the most energy, but all give enough energy for microorganisms to live.

A few notes about liquid methane based life on Titan. First, while such life would produce CH4 it would not be a net source of CH4 but would be merely recycling C back into CH4 – undoing the photochemistry caused by sunlight in the upper atmosphere. It does not explain the persistence of CH4 on Titan over geological time. Second, it is impossible to predict any isotopic effect that this life might have on C. On Earth, methanogens produce CH4 from CO2+H2, or from organic material derived from CO2. The net reaction is CO2 + 4H2 => CH4 + 2H2O and thus methanogens on Earth are a net source of CH4 in a world of CO2. The enzymes that mediate these reactions create methane with a large isotopic enrichment of 12C over 13C of ~5%.

On Titan, it has been predicted that methanogens would produce CH4 by C2H2 + 3H2 => 2CH4 (eg. McKay and Smith 2005). This is obviously not a net source of CH4: it merely recycles CH4, thereby undoing the photolysis of CH4 and there is no a priori reason to expect the resulting CH4 to exhibit an isotopic shift from these reactions. The C-C bond in acetylene is strong but this by itself does not imply a strong isotopic selectivity. For example, life on Earth breaks the strong bond between the N atoms in N2 without leaving a clear isotopic effect. Thus, the istopic state of C on Titan is not relevant to the question of the presence of Titanian methanogens..

The data that suggests that there is less ethane on Titan than expected is well established (Lorenz et al. 2008). Photochemical models have predicted that Titan should have a layer of ethane sufficient to cover the entire surface to a thickness of many meters but Cassini has found no such layer. The new results of Clark et al. (2010) find a lack of acetylene on the surface despite its expected production in the atmosphere and subsequent deposition on the ground. There was also no evidence of acetylene in the gases released from the surface after the Huygens Probe landing (Niemann et al. 2005, Lorenz et al. 2006). Thus, the evidence for less ethane and less acetylene than expected seems clear and incontrovertible.

The depletion of ethane and acetylene become significant in the astrobiological sense because of this latest report of a hydrogen flux into the surface This is the key that suggests that these depletions are not just due to a lack of production but are due to some kind of chemical reaction at the surface. The determination by Strobel (2010) that there is a flux of hydrogen into the surface of Titan is not the result of a direct observation. Rather it is the result of a computer simulation designed to fit measurements of the hydrogen concentration in the lower and upper atmosphere in a self-consistent way. It is not presently clear from Strobel’s results how dependent his conclusion of a hydrogen flux into the surface is on the way the computer simulation is constructed or on how accurately it simulates the Titan chemistry.

In conclusion, there are four possibilities for the recently reported findings, listed in order of their likely reality:
1. The determination that there is a strong flux of hydrogen into the surface is mistaken. It will be interesting to see if other researchers, in trying to duplicate Strobel’s results, reach the same conclusion.
2. There is a physical process that is transporting H2 from the upper atmosphere into the lower atmosphere. One possibility is adsorption onto the solid organic atmospheric haze particles which eventually fall to the ground. However this would be a flux of H2, and not a net loss of H2.
3. If the loss of hydrogen at the surface is correct, the non-biological explanation requires that there be some sort of surface catalyst, presently unknown, that can mediate the hydrogenation reaction at 95 K, the temperature of the Titan surface. That would be quite interesting and a startling find although not as startling as the presence of life.
4. The depletion of hydrogen, acetylene, and ethane, is due to a new type of liquid-methane based life form as predicted (Benner et al. 2004, McKay and Smith 2005, and Schulze-Makuch and Grinspoon 2005).

+ Benner, S.A., A. Ricardo and M.A. Carrigan (2004) Is there a common chemical model for life in the universe? Current Opinion in Chemical Biology 8, 672-689. Clark, R. N., J. M. Curchin, J. W. Barnes, R. Jaumann, L. Soderblom, D. P. Cruikshank, R. H. Brown, S. Rodriguez, J. Lunine, K. Stephan, T. M. Hoefen, S. Le Mouelic, C. Sotin, K. H. Baines, B. J. Buratti, and P. D. Nicholson (2010) Detection and Mapping of Hydrocarbon Deposits on Titan. J. Geophys. Res., doi:10.1029/2009JE003369, in press.
+ Lorenz, L.D., H.B. Niemann, D.N. Harpold, S.H. Way, and J.C. Zarnecki (2006) Titan’s damp ground: Constraints on Titan surface thermal properties from the temperature evolution of the Huygens GCMS inlet. Meteoritics and Planetary Science 41, 1705-1714.
+ Lorenz, R.D., K.L. Mitchell, R.L. Kirk, A.G. Hayes, O. Aharonson, H.A. Zebker, P. Paillou, J. Radebaugh, J.I. Lunine, M.A. Janssen, S.D. Wall, R.M. Lopes, B. Stiles, S. Ostro, G. Mitri, and E.R. Stofan (2008) Titan’s inventory of organic surface materials Geophys. Res. Lett. 35, L02206, doi:10.1029/2007GL032118. McKay, C.P., Smith, H.D. (2005) Possibilities for methanogenic life in liquid methane on the surface of Titan. Icarus, 178, 274-276.
+ Niemann H. B., Atreya S. K., Bauer S. J., Carignan G. R., Demick J.E., Frost R. L., Gautier D., Haberman J. A., Harpold D. N., Hunten D. M., Israel G., Lunine J. I., Kasprzak W. T., Owen T.C., Paulkovich M., Raulin F., Raaen E., and Way S. H. (2005) The abundances of constituents of Titan’s atmosphere from the GCMS instrument on the Huygens probe. Nature 438, 779-784.
+ Schulze-Makuch, D., and D.H. Grinspoon (2005) Biologically enhanced energy and carbon cycling on Titan? Astrobiology 5, 560-564.
+ Strobel, D.F. (2010) Molecular hydrogen in Titan’s atmosphere: Implications of the measured tropospheric and thermospheric mole fractions. Icarus, in press.

Mars Underground: The Harsh Reality of Life Below
by Robert Roy Britt / 08 March 2004

If there is life on Mars, it certainly hasn’t jumped out and mugged for the Mars rovers’ cameras like many people had hoped. And most scientists agree it probably won’t. In fact, any critters that lurk on the red planet today would almost certainly be part of an underground organization that has defied long odds and the harsh realities of a very unfriendly world.

So why all the excitement last week over once soggy rocks at Meridiani Planum? After all, scientists already knew Mars once held a lot of water. The evidence is written all over the planet as scars of river erosion. All that’s really new is scientists now know of a specific location where water was abundant. Yet for some biologists, it isn’t just the signature of ancient water at Opportunity’s landing site that is exciting. It’s also the salt that was left behind. Water and salt — specifically lots of what scientists call sulfates — together can make brine. And brine is great stuff if you are a certain type of microbe. While neither water nor brine actually imply life, fresh shafts of optimism now shine on the possibility that an ancient soup of organic materials might have allowed the genesis of microscopic organisms, which could still dwell in the belly of the red planet.

Pass the salt, please
Road crews lay down salt because it lowers the freezing temperature of water. The same is true of brine. And that’s handy on a planet where the average global temperature is minus 63 degrees Fahrenheit (-53 C). Briney underground reservoirs might have existed for long periods of time, according to computer models. Significant pockets might remain today. Importantly, there are organisms on Earth that thrive in environments so salty they’d make a McDonald’s French fry cringe. They’re called halophiles (pronounced halo-files). Rocco Mancinelli of the SETI Institute studies these salt-resistant organisms. They are hardy, and hardly rare.

In a telephone interview last week, Mancinelli explained that halophiles are represented in all three primary domains of life — Bacteria, Eukarya and Archaea, but that each has developed different ways of dealing with high-salt environments. That suggests the trait “probably arose more than once,” he says, and so it is likely something that originates and develops easily. “Such a trait could easily have evolved in a Martian organism as well,” Mancinelli said. That is, he quickly added, assuming there ever were any Martian organisms. Halophiles are interesting to Mancinelli in part because if life ever did begin on Mars, an evolving ability to endure higher and higher concentrations of salt might have been needed to allow organisms to survive to the present.

Here’s why: Early in its history, Mars almost certainly had more water at or near the surface. There might have been lakes or seas, and probably rivers — at least in brief episodes. If there was no standing surface water, then at least there was more underground water than today, as last week’s rover discovery shows. Where there is water, minerals dissolve in it. When the water on Mars evaporated into outer space or retreated underground — nobody is sure where it all went — what remained would gradually have developed a higher concentration of dissolved salts, Mancinelli explains. “When the concentration gets high enough, most organisms would die,” he said. Halophiles, in this scenario, would get the planet to themselves. In one terrestrial example of this, scientists recently found a previously unknown form of life thriving in California’s Mono Lake, which has been slowly receding for decades, leaving a high concentration of minerals and salt that other organisms can’t take.

The element of time
Mancinelli thinks brine pockets probably remain deep beneath the surface of Mars today. Some might have lasted for hundreds of millions of years. “These brine pockets may be moving around. They may merge and separate.” But their suspected endurance is important, as would have been the duration of any surface seas. Like water, time may be a crucial aspect to life. Nobody knows exactly when or how life on Earth began, but the oldest record of it dates back roughly 3.5 billion years on a planet that’s been around for 4.5 billion years. Mars was born about the same time, just after the Sun formed. For how much of that time on early Earth were the ingredients of life present, and how long did it take Nature to make the jump from chemicals and minerals to living cells? Likewise, how long might it have taken for life on Mars to develop, if it ever did? “I don’t know,” Mancinelli said, “because we really don’t know how long it takes for life to originate and evolve.”

There are suggestions, however. In 1953, Stanley Miller conducted a landmark experiment in biology. Wondering what might have been the original spark for life, he combined methane, hydrogen and ammonia — substances then thought to dominate the young planet — with water, and sent flashes of electricity through it all. Overnight, things changed. In a series of experiments, Miller eventually cooked up 13 of the 31 amino acids needed for life. Neither Miller nor anyone else has figured out what actually triggered life, but the experiments suggested that with certain ingredients and perhaps a little lightning, some pretty magical stuff can happen.

The window for life
Miller believed that once the right raw materials were gathered, life might develop rather quickly. A century would be perhaps unreasonably brief, in his view, but if it didn’t happen in a million years, he reasoned it probably never would. Knowledge of the ingredients of Earth’s early atmosphere has since changed, but still today, Harvard paleontologist Andrew Knoll takes a similar view of time frame for things to get going. “I’d guess that the 10,000 to 1-million-year window is reasonable,” Knoll, a member the Mars rover science team, told “The other question, of course, is what it takes for life to persist on a planet. If water is present only intermittently, then any life that originates has little chance of surviving in the long run.”

Other research has suggested that water might have flooded the surface of Mars in hellish bursts. Nobody can say if that was the case, or if so then how many centuries or millennia the bursts might have lasted. And so far, Opportunity has not determined how long its Meridiani Planum landing site was wet, nor when in the past the rocks were drenched. Further observations from the twin rover mission could provide some clues to this crucial puzzle, however. “If water is present on the Martian surface for 100 years every 10 million years, that’s not very interesting for biology,” Knoll has said in the past. “If it’s present for 10 million years, that’s very interesting.”

Life underground
Even if biology got a foothold on ancient Mars, it is not clear if anything could have persevered long underground, with or without salty survival skills. On Earth, organisms do thrive deep underground — hundreds of feet below — without a single ray of sunshine. They live off chemical energy instead, like methane or hydrogen produced in chemical interactions between water and rock. Being a halophile, it should be noted, is not a condition for being an underground extremophile, as ultra-hardy microbes are collectively known. In fact one organism that might have done well on ancient Mars is desulfotomaculum, which uses sulfur as its energy source, said Benton Clark III, chief scientist of space exploration at Lockheed Martin and a member of the rover team. “It can form spores as well, so it can hibernate over these interim times on Mars between the warmer spells,” Clark said last week in discussing Opportunity’s discovery.

Ultimately desulfotomaculum could not have endured the high salt concentrations that Mancinelli describes. Yet on ancient Mars, the door of life might have been open to creatures of various eating habits and with differing survival schemes. One thing most researchers agree on: the Sun was probably not a prime energy source. Bruce Jakosky is a geologist at the University of Colorado, Boulder and director of its NASA-sponsored Center for Astrobiology. He helped pick the rover landing sites but has not been directly involved in the rover science explorations. Jakosky says it might have made little difference to the question of biology whether the Opportunity landing site was once a sea or just a location of copious ground water. He says the type of organism one might imagine finding at Mars would likely use geochemical sources of energy, rather than sunlight. “On Earth, we think that chemical sources of energy came first, followed by photosynthesis, which is a more complicated process,” Jakosky said. “Chemical energy is available from day one.”

What are the odds?
There could be a huge hitch in all this thinking. Scientists are currently debating whether underground terrestrial life is truly independent of sunlight, or if the chemistry of the surface — including photosynthesis and its products and byproducts — must filter down to make life possible below. “Do those things that [an organism is] surviving on have to be coupled to the surface?” Mancinelli wonders. “The jury is still out.” Knoll, the paleontologist, says many underground bacteria “actually eat buried organic matter and so are inexorably tied to surface photosynthesis, even if indirectly.” He also cautions that life in a subsurface realm might need to routinely get from one oasis to another as a planet changes over time. “You only have to break this chain once for the experiment to end,” Knoll says.

Terrestrial life has proven itself to be ubiquitous and resilient, able to essentially eat rocks if need be, or to eke out an existence under Arctic ice with only intermittently present films of liquid water. It can lay dormant for many thousands of years, awaiting the right environment to allow it to repair its cells and divide into new ones. But could the long-sought little green microbes have endured eons inside Mars? “Underground life is a possibility for Mars’ past and, with much longer odds, perhaps even its present,” Knoll figures. “But in the absence of abundant surface life, I would assign a fairly low probability for the present day persistence of such ecosystems.”

Frozen sea on Mars linked to elevated methane
by Kelly Young and Jenny Hogan / 23 February 2005

The discovery of a frozen sea on Mars has ignited a new debate on whether life existed on the Red Planet. Most intriguing is the claim that the atmosphere above the frozen ocean in the Elysium Planitia region may have elevated concentrations of methane. If true, it could suggest that primitive micro-organisms might even survive on Mars today, according to Jan-Peter Muller, at University College London, UK, and one of the team that found the frozen sea. The team, which was led by John Murray at the Open University, UK, analysed images taken by Europe’s Mars Express spacecraft. “If the ice is still there, then Elysium is the most likely place to find past or present life on Mars,” says Murray. He presented the findings at the 1st Mars Express Science Conference in Noordwijk, the Netherlands, on Monday. Immediately after his talk, Vittorio Formisano, chief scientist for Mars Express’s Planetary Fourier Spectrometer (PFS) which measures the composition of gases in the planet’s atmosphere, commented: “Elysium Planitia is indeed the region where we have seen the maximum of methane coming out of the surface.” On Earth, most of the methane in the atmosphere is produced by microbes living in the soil. Formisano thinks that life is the most likely explanation for methane in the Martian atmosphere, too.

No consensus
NASA planetary scientist Chris McKay, who was not part of the research group, agrees that the site is an important one in the search for life. “If these are really locations where there was an ice-covered ocean, I think this would be a very interesting place to drill for evidence of past life.” But McKay warns that scientists have yet to reach a consensus about the presence of a high level of methane on Mars. Estimates of the expected lifetime of the gas in the atmosphere are uncertain, and may be off by a factor of 10,000. It is also possible that what scientists think is methane may be something else entirely, he says. And other scientists note that finding water would not necessarily equate to past or present life. “I think it’s way too early to jump to conclusions,” says Kenneth Nealson, a geobiology professor at the University of Southern California, Los Angeles, US. “Water is required for life, but it in no way indicates that there is life.”

Isotopic signature
The observations by Mars Express’s PFS instrument indicate concentrations of about 10.5 parts per billion in the Elysium Planitia region. Even if it is more concentrated in that area, it could just as easily be a product of geological activity as microbial life, Nealson adds. Elysium Planitia is one of the major volcanic regions on Mars. “If you had the isotopic signature of the methane, you might be on firmer ground,” he says, as this could indicate if the methane was formed biologically. Formisano has also reported, in September 2004, that concentrations of water vapour near the Martian surface are two to three times higher along three regions near the equator, including Elysium Planitia, than at higher altitudes. Those concentrations also correspond to results from NASA’s Mars Odyssey spacecraft, which sniffed out hydrogen in the uppermost metre of Martian soil and rock.


A microorganism that produces methane as a byproduct of its metabolism. All known methanogens are both archaeans and obligate anaerobes, that is, they cannot live in the presence of oxygen. They are commonly found in wetlands, where they generate methane in the form of marsh gas, and in the guts of animals such as ruminants and humans, where they are responsible for flatulence. Some methanogens, described as hydrotropic, use carbon dioxide as a source of carbon and hydrogen as a source of energy. Some of the carbon dioxide reacts with, and is reduced by, hydrogen to produce methane. The methane is turn gives rise to a proton motive force across a membrane, which is used to generate ATP – a key source of cellular energy. Other methanogens, called acetotrophic, use acetate (CH3COO-) as a source of both carbon and energy. Still other methanogens exploit methylated compounds such as methylamines, methanol, and methanethiol as well. More than 50 species of methanogens have been identified, including a number that are extremophiles. Live methanogens were recovered from a core sample taken from 3 kilometers under Greenland by researchers from the University of California, Berkeley. Another study discovered methanogens in soil and vapor samples from the vicinity of the Mars Desert Research Station in Utah. These findings add weigh to speculation by some scientists that methanogens may be responsible for the methane that has been in detected in the atmosphere of Mars.

Methane rivers and rain shape Titan’s surface
by Stephen Battersby / 21 January 2005

Hills made of ice and rivers carved by liquid methane mark the surface of Saturn’s giant moon, reveal data from the Huygens probe. Scientists are now beginning to get a coherent picture of Titan after the probe landed there on 14 January. The coldest world that humanity has ever explored bears a strange resemblance to Earth, boasting hills, river systems, and mud flats. The probe survived an unexpectedly bumpy ride through the atmosphere of Titan but enjoyed a soft landing, settling several centimetres into the surface, Huygens’ scientists revealed at the European Space Agency’s headquarters in Paris on Friday.

They have now analysed many of the images returned by Huygens’ cameras. In one small region just 1 kilometre across, the camera team have combined images to get a 3D view of Titan’s ice hills. “We see a ridge system with a peak 100 metres tall,” says Marty Tomasko of the University of Arizona, US, and head of the Huygens imaging team. There is even a hint of how the hills are built: “In another region we see a white streaky pattern, evidence of water ice being extruded by the surface.” Dark channels cutting across this area are now clearly revealed as drainage systems. “We see a river system that flows down into a delta. There are also short, stubby channels indicative of springs flowing out of the hillsides,” says Tomasko.

Flammable world
Scientists speculated long ago that some kind of hydrocarbon liquids might flow on Titan. “We’ve learned that our speculation was really pretty good,” says Toby Owen, of the University of Hawaii, an expert on Titan’s atmosphere. They now know that the fluid that carved the moon’s rivers and channels is methane. Huygens’ chemical analyser saw that methane gas becomes more concentrated lower in Titan’s atmosphere, just like water vapour on Earth. After landing, Huygens’ gas chromatograph and mass spectrometer instrument saw methane concentrations jump by 30%. The gas was probably evaporated from the muddy soil by heat from the European Space Agency’s probe. “It means there’s methane near the surface,” says Owen, “Titan is a flammable world.” But all the oxygen is trapped in ice. “That’s a good thing, or Titan would have exploded a long time ago.” While there are many signs of liquid on Titan, there is none currently visible to Huygens. “Titan may be typical of arid regions of Earth like Arizona, where riverbeds are dry most of the time,” says Tomasko. “Perhaps there’s a wet season once a year. We just don’t know.”

Exotic materials
The mud may be a mixture of ice, sand, methane and complex organic molecules that form in the upper atmosphere. “This smog falls out of the atmosphere and settles on everything. Then methane rain comes, washes it off the ice ridges and into rivers, then out into a broad plain where the rain settles into the ground and dries up. We are seeing evidence of Earth-like processes but with very exotic materials,” says Tomasko. There are plenty of mysteries still to unravel. Methane is constantly being destroyed and turned into a complex chemical smog, so there must be some methane source inside Titan to replenish the atmosphere. And certain gases, including argon, are inexplicably absent from Titan’s atmosphere, which may be a clue to how the moon formed. However, Huygens has seen only one small patch of the surface – which might turn out to be unusual – it might even have come down in a desert. “This is one single place on an interesting and varied world,” says Owen. Jean-Pierre Lebreton, the Huygens mission manager hopes that the probe will inspire a new mission to Titan: “The next capability to bring to Titan is mobility. We can now seriously dream of sending rovers to its surface. Or flying machines, or balloons to float around the moon. We just need the money.”

Life on Titan ?

Over the past few years, the scientific community has realized that numerous forms of life evolve in extreme conditions on Earth.For instance, we found out bacteria being able to support temperatures up to 113°c and living in boiling water of thermal sources. We also found fishes living in the abyss of oceans and supporting pressures 500 times higher than the atmospheric pressure.Another example: the well known Yellowstone National Park ( USA ) is filled with billions of bacteria living in water whose temperature is around 70°c.

The intensive exploration of the most inhospitable places on Earth has shown that what we call now the extremophiles are capable of living without sunlight or oxygen.Where there is not much oxygen and no sunlight, one can encounter blind spiders or other insects with no pigment and being able to draw their energy from the mixture of hydrogen and sulfur released by volcanic chimneys.All those observations push us into thinking that any exotic life is a possibility in other hostile worlds like Europa,Titan or even Jupiter.

Titan seems to be a very hostile sphere, notably in terms of temperature.Our temperature model derived from the Stefan’s law shows that the surface temperature is expected to be around -114°c ( 159K or -173°F) on the basis of an atmospheric pressure of 1.5 bars.Hence, the atmosphere is likely to generate a greenhouse effect that increases the environmental temperature by about 74°c.It’s unsufficient to allow the presence of liquid water on the surface.Now, liquid water appears to be the essential solvent from which life has emerged.But, on Titan, contrary to the other bodies in the Solar System, a liquid of hydrocarbon ( ethane, methane…) or ammonia might be present at the surface, perhaps allowing the development of organic molecules, amino acids,proteins or DNA.It is often said that Titan puts together the ingredients of the primitive soup, the chemistry that led to life on Earth. A famous laboratory experiment was carried out in the 1950’s by Stanley Miller to try to figure out the secrets of the origin of life. He submitted a mixture of methane ( CH4), hydrogen ( H2), ammonia (NH3) and water vapour ( H2O) to electric sparks for many days in a closed system. The sparks were supposed to represent lightning in the early stages of our planet and the previous molecules were believed to represent the major components of the early Earth’s atmosphere.After several days of electric sparks, he obtained organic compounds ( HCN, HCHO…) and amino acids which are used to make proteins.Did this process occured on Titan? It’s hard to say but one thing is striking : the resemblance between Titan’s atmosphere and Earth’s atmosphere.The atmosphere of those two bodies is mostly composed of nitrogen ( 78% for Earth and around 90% for Titan ) contrary to Venus and Mars which are mostly composed of carbon dioxide.Nevertheless, Titan is very poor in oxygen meaning that there is no life breathing oxygen or using oxygen in the feeding process.

A form of life on Titan?
If there is life on Titan, what might it look like? An answer implies that we analyse the basis and the environment of life on Earth and that we try to imagine the elements of the Titan crust. On Earth, water acts not only as a solvent for the living creatures to combine, it is also the major compound of life herself.For instance, plants and jelly fishes have an abundance of water higher than 90% of their weight. Human beings are also mostly composed of water in a proportion of around 65%.To sum up, it is hard to conceive that life can be envisaged without the water molecule. Likewise, it is also hard to admit that we can encounter a form of life which is not based on the carbon element since it is present in large amounts in every species on Earth. Carbon is the second major constituent of life: it represents around 30% of the human weight and calcium, magnesium and other oligo elements are in a very small proportion. Another particularity of life is that it is always based on DNA ( Deoxyribo Nucleic Acid ) except that one knows one exception.The fact that water is the most common molecule on Earth leads us to say that life has emerged by using what was the most common molecule. However, carbon is relatively rare in our environment while it is abundant in every living creature. Carbon has chemical and physical properties that enable it to combine very well with oxygen, hydrogen or water which is less the case for Silicon. That is the reason why an element so rare in the crust of our planet has contributed to build the most complex molecular structures in nature.

On Titan, the most fundamental differences with Earth are the gravity and the distance to the Sun. Most scientists believe that there would be no life on Earth if the sphere were 5% farther from the Sun or 1% closer to the Sun.Too far from the Sun and the planet would be too cold for life to evolve and too close and our planet would resemble Venus. But Titan is so much different that the theories that apply to Earth may not work for Titan.Titan presents a major advantage of being protected from the noxious solar radiations by a very thick atmosphere largely denser than our own atmosphere.On this point, it is a less hostile environment for any living creature to evolve than Mars, for example.Nevertheless, as we’ve said, the temperature on Titan might be below -100°c erasing the probability of discovering liquid water in some place though thermal sources are likely to raise this possibility.With a solvent like ethane or methane, one can imagine a completely different chemistry of life from what we know.The species would not absorb oxygen like human beings or carbon dioxide like plants as carbon dioxide is frozen and oxygen is very rare.According to Marc Lafferre and Guilhem Cournot, one might encounter living creatures absorbing hydrocarbon gas ( methane, ethane…) which are relatively common in the atmosphere ( around 5% of the atmosphere’s composition) and releasing hydrogen which will recombine again with nitrogen or hydrocarbon molecules in the atmosphere to form other hydrocarbon molecules or ammonia under the action of ultraviolet light that splits the molecules.Hence we could see lakes or oceans of hydrocarbon ( ethane, methane…) with glaciers of ammonia rich ice resulting from a snow of ammonia falling from time to time.Living species would consist mostly of hydrocarbon ( methane…).So, the major elements of life would be carbon and hydrogen.The oxygen would be present in a smaller proportion in the structure of life because of the low environmental temperatures that favour combinations with carbon and hydrogen rather than hydrogen with oxygen or carbon with oxygen which are frozen on the surface of Titan ( frozen carbon dioxide and frozen water ).The french chemist André Brack in 1993 pointed out that a form of life based on silicon could be envisaged : the species would be mostly composed of silicon, an element very abundant in the soil ( around 25% of the composition of the crust on Earth ).In other words, the creatures would be made of sand.They would breathe oxygen or hydrogen and would release silicon dioxide ( Si O2 ) or Si H2. Silicon like carbon has the ability to create bonds simultaneously with four other elements and to give birth to multiple molecules. However, the bonds are particularly rigid compared to carbon.As a result, the species would be very limited and their development and adaptation capabilities would be slown down. The main advantage of this form of life would be to resist higher environmental temperatures.On Titan, the low temperatures diminish the probability of encountering this hypothetical form of life.On the other hand, Venus could have harboured that kind of life because of the very hot environmental temperatures.Furthermore, on Titan, a form of life involving the chemistry of nitrogen and ammonia appears less credible since carbon doesn’t play a key role in this configuration.

If the distance plays a crucial role for the appearance of life, the gravity of the saturnian moon plays a key role for the way life will develop and evolve.The low gravity of Titan allows creatures to be thinner with thin bones if they have bones.To sustain their own weight, they don’t need to have powerful legs or paws.The fish moves in a liquid less dense than water.So, he has no interest of being heavy and short according to the Archimedes’ Law. As said Ralph Lorenz, Titan is a heaven for hypothetical birds: they benefit from a low gravity and a thick air.They can be heavier than on Earth and their wings can be shorter which is also better in a cold environment.A denser air enables birds to carry out fewer movements of the wings to advance at the same speed.

It seems, today, that the environmental temperature on Titan is by far too cold to allow the development of an Earth like life, based on water and carbon.But the evolution of the Solar System and the Sun could become more and more favourable for the development of a life on Titan very soon.According to Chris Mc Kay,who studied notably the possibilities of terraforming on Mars,Titan might become warm enough, over the next five billion years, to host life. The Sun is expected to cool down very progressively and in a few billion years, it will become a red giant, a less energetic star, extending far beyond the orbit of our planet.As a result, it will be largely closer to Titan and the amount of energy received by the satellite, though less energetic, will be sufficient to raise the overall temperature so that water appears in its liquid form.Less ultraviolet light will attain the atmosphere of Titan so that the shield of red haze that resulted from the action of those particles and that prevented the light from reaching the soil will disappear and an Earth like meteorology will emerge.The current prebiotic molecules will then be able to combine and evolve towards the development of amino acids, proteins and life.

A model for methane based life
In this model developed by Marc Lafferre and Guilhem Cournot ( 2004 ), the mean temperature at the surface of the satellite is around -114°c ( -173°F or 159K). This temperature is well above the theoritical temperature thanks to a greenhouse effect that raises the temperature by about 73°c (163°F or 346K).This mean temperature is too high to allow the presence of liquid methane despite high pressures that delay the boiling point.On the other hand, seas and lakes of ethane rich hydrocarbon can be observed.Ethane ( C2H6 ) is in its liquid form between -88°c and -183°c.So, the evaporation process is weak. The atmosphere consists mostly of nitrogen and contains a large amount of one of the most powerful greenhouse gases one knows,that is to say methane ( CH4) which represents up to 5% of the atmosphere. The ultraviolet radiations from the Sun engender complex photochemical reactions in the upper atmosphere by breaking the methane molecules ( CH4) into various compounds such as acetylene ( C2H2) or Ethane (C2H6) which combine with other molecules to form tholin,a kind of red sludge.The ethane molecules formed in the upper atmosphere will then fall as rain in small quantities.

Under those circumstances, an ecosystem based on methane has emerged.The solvent that enabled life to develop on Earth, that is water, is replaced here by liquid hydrocarbon. The living creatures have not developed on the basis of water or carbon dioxide since both molecules are frozen at the surface of Titan. In other words, the species are not made up of water ( H2O ) contrary to life on Earth. The key compounds of life on Titan are carbon, hydrogen,methane and ethane.Those elements or molecules are more flexible and more volatile than oxygen and water in the harsh local climate conditions.The creatures absorb the hydrocarbon liquid as we absorb water and most of them, including plants, breathe the methane gas to produce the organic material and expire H2.The birds, for instance, drink “ethane rich hydrocarbon liquid”, breathe H2 released by plants and expire CH4.In a sense, that would be the biological cycle of methane.

As the solar energy reaching the Titan soil is very weak at this distance from the Sun, the forms of life prospering on Titan are less pigmented than on Earth.Obviously, we don’t encounter animals as colourful as the animals we can see in a tropical area on Earth. Finally, animals tend to have white or slightly red colours.They have developed a biological structure that enable them to store and manage the little energy they receive.Furthermore,they benefit from a low gravity: that’s the reason why the skeleton of Titan mammals is generally thinner than that of Earth’s mammals.Titan is a paradise for birds: they benefit not only from a low gravity, seven times smaller than on Earth, but also from a dense air which makes possible a smaller frequency in the movement of wings.Thereby, the bird spends less energy to fly though the air is heavier and more difficult to displace.

Hence, Titan appears to be a major source of speculation and research for exobiologists in their quest for the secrets of the origin of life.No doubt that the exploration of Titan will allow us to better understand the chemistry of every planet in the Solar System and perhaps the chemistry that led to life on Earth.

Electrical Activity On Saturn’s Moon Titan Confirmed By Spanish Scientists / July 29, 2008

Physicists from the University of Granada and University of Valencia have developed a procedure for analysing specific data sent by the Huygens probe from Titan, the largest of Saturn’s moons, “unequivocally” proving that there is natural electrical activity in its atmosphere. The scientific community believe that the probability of organic molecules, precursors of life, being formed is higher on planets or moons which have an atmosphere with electrical storms. The researcher, Juan Antonio Morente, from the Department of Applied Physics at the University of Granada, indicated to SINC that Titan has been considered a “unique world in the solar system” since 1908 when, the Spanish astronomer, José Comas y Solá, discovered that it had an atmosphere, something non-existent on other moons. “On this moon clouds with convective movements are formed and, therefore, static electrical fields and stormy conditions can be produced”, he explained. “This also considerably increases the possibility of organic and prebiotic molecules being formed, according to the theory of the Russian biochemist Alexander I. Oparín and the experiment of Stanley L. Miller”, which managed to synthesise organic compounds from inorganic compounds through electrical discharges. “That is why Titan has been one of the main objectives of the Cassini-Huygens joint mission of NASA and the European Space Agency”, added the researcher. Morente indicated that in order to detect natural electrical activity on planets such as Earth or moons such as Titan the so-called “Schumann resonances”, a set of spectrum peaks in the extremely low frequency (ELF) portion of the radio spectrum, are measured. These peaks are produced due to the existence between the ionosphere and the surface of a huge resonant cavity in which electromagnetic fields are confined. They present two basic components: a radial electrical field and a tangential magnetic field, accompanied by a weak tangential electrical field (one hundred times smaller than the radial component).

The electrical field was measured by the mutual impedance probe (MIP), one of the instruments transported by the Huygens probe. The MIP consisted of four electrodes, two transmitters and two receptors, with a transmitter-receptor pair on each one of the probe’s folding arms. The MIP was primarily used for measuring the atmosphere’s electrical conductivity, but between each measurement of this physical magnitude it also acted as a dipolar antenna, measuring the natural electrical field in the atmosphere. “In a stable fall, without balancing, the MIP would have measured the electrical field’s weak tangential component”, said Morente, “but fortunately a strong wind balanced the probe and the electrodes measured a superposition of that tangential and radial component”. Despite this, the electrical field spectrums received directly from Huygens did not follow the patterns the scientists expected, as they were relatively flat and no Schumann resonances were observed. However, the team of Spanish researchers did manage to devise a procedure for revealing the hidden Schumann resonances, based on the separation of time signals known as “early” and “late-time”, which made it possible to obtain “irrefutable proof” that natural electrical activity does exist in Titan’s atmosphere. In the work, subsidised by the former Ministry of Education and Science, Government of Andalusia and the European Union, it was also explained that the atmosphere of this one of Saturn’s moon is an electromagnetic medium with high losses, and that its resonant cavity is less ideal than the Earth’s.


In 1954, J. B. S. Haldane, speaking at the Symposium on the Origin of Life, suggested that an alternative biochemistry could be conceived in which water was replaced as a solvent by liquid ammonia.1 Part of his reasoning was based on the observation that water has a number of ammonia analogues. For example, the ammonia analogue of methanol, CH3OH, is methylamine, CH3NH2. Haldane theorized that it might be possible to build up the ammonia-based counterparts of complex substances, such as proteins and nucleic acids, and then make use of the fact that an entire class of organic compounds, the peptides, could exist without change in the ammonia system. The amide molecules, which substitute for the normal amino acids, could then undergo condensation to form polypeptides which would be almost identical in form to those found in terrestrial life-forms. This hypothesis, which was developed further by the British astronomer V. Axel Firsoff,2, 3 is of particular interest when considering the possibility of biological evolution on ammonia-rich worlds such as gas giants and their moons.

On the plus side, liquid ammonia does have some striking chemical similarities with water. There is a whole system of organic and inorganic chemistry that takes place in ammono, instead of aqueous, solution.4, 5 Ammonia has the further advantage of dissolving most organics as well as or better than water,6 and it has the unprecedented ability to dissolve many elemental metals, including sodium, magnesium, and aluminum, directly into solution; moreover, several other elements, such as iodine, sulfur, selenium, and phosphorus are also somewhat soluble in ammonia with minimal reaction. Each of these elements is important to life chemistry and the pathways of prebiotic synthesis. The objection is often raised that the liquidity range of liquid ammonia – 44°C at 1 atm pressure – is rather low for biology. But, as with water, raising the planetary surface pressure broadens the liquidity range. At 60 atm, for example, which is below the pressures available on Jupiter or Venus, ammonia boils at 98°C instead of -33°C, giving a liquidity range of 175°C. Ammonia-based life need not necessarily be low-temperature life!

Ammonia has a dielectric constant about ¼ that of water, making it a much poorer insulator. On the other hand, ammonia’s heat of fusion is higher, so it is relatively harder to freeze at the melting point. The specific heat of ammonia is slightly greater than that of water, and it is far less viscous (it is freer-flowing). The acid-base chemistry of liquid ammonia has been studied extensively, and it has proven to be almost as rich in detail as that of the water system. In many ways, as a solvent for life, ammonia is hardly inferior to water. Compelling analogues to the macromolecules of Earthly life may be designed in the ammonia system. However, an ammonia-based biochemistry might well develop along wholly different lines. There are probably as many different possibilities in carbon-ammonia as in carbon-water systems.7 The vital solvent of a living organism should be capable of dissociating into anions (negative ions) and cations (positive ions), which permits acid-base reactions to occur. In the ammonia solvent system, acids and bases are different than in the water system (acidity and basicity are defined relative to the medium in which they are dissolved). In the ammonia system, water, which reacts with liquid ammonia to yield the NH+ ion, would appear to be a strong acid – quite hostile to life. Ammono-life astronomers, eyeing our planet, would doubtless view Earth’s oceans as little more than vats of hot acid. Water and ammonia are not chemically identical: they are simply analogous. There will necessarily be many differences in the biochemical particulars. Molton suggested, for example, that ammonia-based life forms may use cesium and rubidium chlorides to regulate the electrical potential of cell membranes. These salts are more soluble in liquid ammonia than the potassium or sodium salts used by terrestrial life.8

On the down side, there are problems with the notion of ammonia as a basis for life. These center principally upon the fact that the heat of vaporization of ammonia is only half that of water and its surface tension only one third as much. Consequently, the hydrogen bonds that exist between ammonia molecule are much weaker than those in water so that ammonia would be less able to concentrate non-polar molecules through a hydrophobic effect. Lacking this ability, questions hang over how well ammonia could hold prebiotic molecules together sufficiently well to allow the formation of a self-reproducing system.9

1. Haldane, J. B. S. “The Origins of Life,” New Biology, 16, 12-27 (1954).
2. Firsoff, V. A. Life Beyond the Earth: A Study in Exobiology. New York: Basic Books (1963).
3. V. Axel Firsoff, “An Ammonia-Based Life,” Discovery 23, 36-42 (January, 1962).
4. Gerhart Jander, Hans Spandau, C. C. Addison; eds. Chemistry in Nonaqueous Ionizing Solvents. New York: John Wiley, Interscience (1966).
5. Smith, Herchel. Organic Reactions in Liquid Ammonia. New York: John Wiley, Interscience (1950).
6. Franklin, E. C., “The Ammonia System of Acids, Bases, and Salts,” American Chemical Journal, 47, 285 (1912).
7. Firsoff, V. A., “Possible Alternative Chemistries of Life,” Spaceflight, 7, 132-136, (July, 1965).
8. Molton, P. M., “Terrestrial Biochemistry in Perspective: Some Other Possibilities,” Spaceflight, 15, 134-144 (April 1073).
9. Feinberg, Gerald, and Shapiro, Robert. Life Beyond Earth: The Intelligent Earthling’s Guide to Life in the Universe. New York: William Morrow (1980).



All known life on Earth is built upon carbon and carbon-based compounds. Yet the possibility has been discussed that life elsewhere may have a different chemical foundation – one based on the element silicon.

Early speculation
In 1891, the German astrophysicist Julius Scheiner became perhaps the first person to speculate on the suitability of silicon as a basis for life. This idea was taken up by the British chemist James Emerson Reynolds who, in 1893, in his opening address to the British Association for the Advancement of Science,1 pointed out that the heat stability of silicon compounds might allow life to exist at very high temperatures (see thermophiles). In an 1894 article,2 drawing on Reynolds’s ideas and also those of Robert Ball,3 H. G. Wells wrote:

One is startled towards fantastic imaginings by such a suggestion: visions of silicon-aluminium organisms – why not silicon-aluminium men at once? – wandering through an atmosphere of gaseous sulphur, let us say, by the shores of a sea of liquid iron some thousand degrees or so above the temperature of a blast furnace.

Thirty years later, J. B. S. Haldane suggested that life might be found deep inside a planet based on partly molten silicates, the oxidation of iron perhaps providing it with energy.

Silicon biochemistry?
At first sight, silicon does look like a promising organic alternative to carbon. It is common in the universe and is also a p-block element of group IV, lying directly below carbon in the periodic table of elements, so that much of its basic chemistry is similar. For instance, just as carbon combines with four hydrogen atoms to form methane, CH4, silicon yields silane, SiH4. Silicates are analogs of carbonates, silicon chloroform of chloroform, and so on. Both elements form long chains, or polymers, in which they alternate with oxygen. In the simplest case, carbon-oxygen chains yield polyacetal, a plastic used in synthetic fibers, while from a backbone of alternating atoms of silicon and oxygen come polymeric silicones.

Conceivably, some strange life-forms might be built from silicone-like substances were it not for an apparently fatal flaw in silicon’s biological credentials. This is its powerful affinity for oxygen. When carbon is oxidized during the respiratory process of a terrestrial organism (see respiration), it becomes the gas carbon dioxide – a waste material that is easy for a creature to remove from its body. The oxidation of silicon, however, yields a solid because, immediately upon formation, silicon dioxide organizes itself into a lattice in which each silicon atom is surrounded by four oxygens. Disposing of such a substance would pose a major respiratory challenge.

Life-forms must also be able to collect, store, and utilize energy from their environment. In carbon-based biota, the basic energy storage compounds are carbohydrates in which the carbon atoms are linked by single bonds into a chain. A carbohydrate is oxidized to release energy (and the waste products water and carbon dioxide) in a series of controlled steps using enzymes. These enzymes are large, complex molecules (see proteins) which catalyze specific reactions because of their shape and “handedness.” A feature of carbon chemistry is that many of its compounds can take right and left forms, and it is this handedness, or chirality, that gives enzymes their ability to recognize and regulate a huge variety of processes in the body. Silicon’s failure to give rise to many compounds that display handedness makes it hard to see how it could serve as the basis for the many interconnected chains of reactions needed to support life.

The absence of silicon-based biology, or even silicon-based prebiotic chemicals, is also suggested by astronomical evidence. Wherever astronomers have looked – in meteorites, in comets, in the atmospheres of the giant planets, in the interstellar medium, and in the outer layers of cool stars – they have found molecules of oxidized silicon (silicon dioxide and silicates) but no substances such as silanes or silicones which might be the precursors of a silicon biochemistry.

Even so, it has been pointed out, silicon may have had a part to play in the origin of life on Earth. A curious fact is that terrestrial life-forms utilize exclusively right-handed carbohydrates and left-handed amino acids. One theory to account for this is that the first prebiotic carbon compounds formed in a pool of “primordial soup” on a silica surface having a certain handedness. This handedness of the silicon compound determined the preferred handedness of the carbon compounds now found in terrestrial life. An entirely different possibility is that of artificial life or intelligence with a significant silicon content.

Notwithstanding the gloomy prognosis from chemists, silicon-based life has flourished in the imaginary worlds of science fiction. In one of its earliest outings, Stanley Weisbaum’s A Martian Odyssey, the creature in question is half a million years old and moves once every ten minutes to deposit a brick – Weisbaum’s answer to one of the major problems facing siliceous life. As one of the watching scientists observes

Those bricks were its waste matter… We’re carbon, and our waste is carbon dioxide, and this thing is silicon, and its waste is silicon dioxide-silica. But silica is a solid, hence the bricks. And it builds itself in, and when it is covered, it moves over to a fresh place to start over.

1. Reynolds, J. E. Nature, 48, 477 (1893).
2. Wells, H. G. “Another Basis for Life,” Saturday Review, p. 676 (December 22, 1894).
3. Ball, R. S. W. “The Possibility of Life in Other Worlds,” Fortnightly Review, 62 (NS 56), 718 (1894).
4. Alison, A. “Possible Forms of Life,” Journal of the British Interplanetary Society, 21, 48 (1968)