Martian methanogens?

There is methane in the Martian atmosphere, and it varies seasonally.

A NASA press release announced the discovery that methane – CH4 – in the atmosphere of Mars appears to vary temporally and spatially. Methane concentrations were measured spectroscopically using NASA’s Infrared Telescope Facility and the W.M. Keck telescope at Mauna Kea, Hawaii. The results over several Mars years show that more CH4 finds its way into the Martian atmosphere during summer there, and also there’s more CH4 in the northern hemisphere than in the southern. This could be a biological signature.

NASA is understandably and correctly cautious in its interpretation of this data.

“Right now, we do not have enough information to tell whether biology or geology — or both — is producing the methane on Mars,” Mumma said. “But it does tell us the planet is still alive, at least in a geologic sense. It is as if Mars is challenging us, saying, ‘hey, find out what this means.’ “

On Earth the majority of methane released into the atmosphere through natural processes is from methanogens, microbes that exhale methane gas as they respire. All methanogens on Earth belong to the ancient line of microbes called Archaea, which closely resemble the common ancestor of all terrestrial life. Some methane is also produced on Earth by volcanoes, and methane is also released by mining natural gas and other fossil fuels. The latter is biologically-derived, too, though volcanic CH4 is purely geological in origin.

Mars is thought to be volcanically dead, so geologic methane sources are unexpected there. An underground biosphere of microbes could account for the CH4, which might build up beneath the permafrost and seasonally diffuse into the atmosphere when the ground warms and partially melts the otherwise impermeable regolith ice. On Mars the photochemistry is wrong for making methane in the atmosphere, so the source has to be in the subsurface.

This isn’t definitive proof of life, but it is mightily odd. It would be plausible to perhaps see a one-off event where a little CH4 seeps from ancient subsurface methane ice. But a repeating temporal pattern of methane coming out of the ground every summer would be very difficult to explain as a purely geological process. If there were tons and tons of buried methane ice dating from 4 billion years ago that might be possible, if deposits were close to the surface… but so much buried methane ice would also be a dead giveaway that the planet once had an active biosphere, even if life is extinct there today.

A definitive answer is attainable, but it would require another mission. Isotopic data could be used to determine whether the CH4 in Mars’ atmosphere is biological or geological in origin. Methane produced biologically on Earth – and almost certainly anywhere else – has isotopically light carbon. Stable carbon normally comes in two isotopes, 12 and 13. Biological processes prefer the light isotope very slightly, which means that methane exhaled from microbes has a distinct carbon isotopic signature relative to volcanic methane. The Martian methane mystery could be solved with just a few measurements, but that would require a new probe with a built-in carbon mass spectrometer with which to sample the atmosphere and regolith.

Right now I’d put the odds of extant life on Mars at ~60%, based on this report and everything else we know about the planet. I’d put the odds of life having been there at least in the remote past at 80%, perhaps 90% after a few margaritas. But if the carbon isotopic data someday comes back with Martian CH4 having a δ13C of -20? Then I’d put the odds at 99% for Mars bacteria. Nobody’s getting 100% until they can capture, culture and sequence the damn things.


~ by Planetologist on January 17, 2009.

2 Responses to “Martian methanogens?”

  1. I’m with you, I am pretty sure methanogens will be found in the subsurface of Mars. I think they will also be found on many other objects in the Solar System – particularly on the moons of Jupiter and in comets too. In fact they may power the motion of comets by the release of methane plumes. Their other end product, water vapour, may account for the ice on comets. When we do confirm these creatures are indeed in these places, the question will then be – how did they get there? – because there is little likelihood of them all evolving independently – they would need to have a common ancestor. In my theory of Planetary Metamorphosis, I suggest that planets have a life cycle wherein they are born as gas clouds on the outer edge of the solar system and gradually migrate inwards towards the Sun, mopping up debris and hydrogen on their way and thereby gaining mass. They pass through stages like the gas planets of Neptune through to Jupiter. Within these gas planets is a rocky nucleus forming. At a critical AU, the hydrogen gas envelope dissipates revealing the rocky nucleus of the Mars stage.To cut a long story short, the planets eventually get too near the Sun and either disintegrate or are fired off into the solar system like a pin-ball. What I am saying is that methanogens could have evolved from inorganic chemistry on a planet which no longer exists.If Mercury is the oldest and closest to the Sun, the planet or two before Mercury could have evolved these archaeans. Subsequent destruction of the planet could have seeded our planet four billion years ago with methanogens within asteroids (planetary debris). Methanogens, as you know, can survive deep within rock (7 kilometres down within the Earth) and so it is feasible that they could be protected from the heat of entry as a large asteroid lands on Earth. This Theory allows for a longer time frame for life to form – as although methanogens are amongst the most primitive of life they are still quite complex.

    • Andrew thanks for the comment. I’m not sure if what you wrote is a spoof, or not… but I have to say that what you describe is simply not how planets form. I’m glad you’re interested enough in the topic to put some thought into it… I wish more people would take the time to do that. But before you go too far into building models, you should know that there is a massive scientific literature on this topic, and the major aspects of planetary formation are fairly well established. If you’re into this kind of stuff, I might recommend any of the books of Neil deGrasse Tyson or Phil Plait. Both are astronomers who’ve spent a lot of time putting some more arcane scientific details of modern astronomy into formats that non-specialists can really enjoy. Phil Plait’s Bad Astronomy blog is a constant source of news and info about stars and galaxies. I try to stick to astrobiology and planetary science in my own blog, here…. when it comes to space science.

      I’d also recommend Wikipedia, which isn’t perfect but does have pretty good information about solar system formation, planetary accretion, and the science of life’s origins.

      On the topic of life starting elsewhere in the solar system, there really aren’t that many options. Mars is an option, but the evidence of life there is still weak… about the only thing we can say definitely so far is that life beginning on Mars isn’t ruled out. Life might also have started inside Europa or Titan, or perhaps even inside Enceladus… although I’m more doubtful than I used to be about life independently starting in the outer solar system. Phosphorus is likely to be a problem, for example.

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