The Mystery of the Martian Methane

I’ve written before about how I think that Mars is creepy. I also wrote then about the disputed claims of methane in the martian atmosphere. Well, as anyone with half an eye on the astronomical blogosphere will probably know by now, those claims are no longer disputed. It’s a fact — somewhere on Mars is a source of methane. The big dry dustball just got interesting. That doesn’t stop me finding it creepy though…

For full details on the discoveries on Mars, there’s a Universe Today article written by Nancy Atkinson, or an article direct from Science@NASA. I’ll bet those NASA scientists are jubilant. This discovery must be like a holy grail to them!
(Well… Maybe not. But they might refer to it that way.)

So, to cut a long story short, three “hotspots” in the Northern hemisphere of Mars, just above the equator, have been shown to be emitting plumes of methane gas (discovered via spectroscopy!). Specifically south-east Syrtis Major, Nili Fossae and Arabia Terra (in case you happen to have a map of Mars handy). Areas which once upon a time, had copious water.

The thing is, methane is quite rapidly destroyed by ultraviolet light, meaning that any noticeable amount of methane on Mars wouldn’t last more than about 340 years. Over the lifetime of a planet, that’s barely the blink of an eye, so the only logical explanation is that there’s a continual supply of methane. A significant amount of methane, at that. What’s more, the effect seems to be seasonal. In the martian summer, more methane is emitted. Subsequently, the gas apparently dissipates faster than sunlight alone can reasonably explain.
A huge disequillibrium in a planet’s atmosphere like this means, very simply, there’s something going on that we don’t understand. And that’s exciting. In my opinion, not being able to explain something is the most exciting part of planetary exploration! Whatever happens, we’ll discover something. And there are only two possible sources of methane gas on planet Mars. Geochemistry or life. Amazingly, as far as I can make out, they both seem equally plausible!

Serpentinisation

So to keep the cynics happy first, let’s explore the idea of geochemical processes creating methane. The main contender is a process called serpentinisation. Serpentine is a kind of silicate mineral. A magnesium-iron phyllosilicate, to be precise. It has a deep olive green lustre to it, and it’s fairly common here on Earth (certain beaches in Cornwall are littered with it). Serpentine has the chemical formula (Mg, Fe)3Si2O5(OH)4 (that might look a little scary to a non-chemist, but bear with me here). It forms when olivine (a much simpler silicate) reacts with water and carbon dioxide;

(Mg, Fe)2SiO4 + CO2 + nH2O → Mg3Si2O5(OH)4 + Fe3O4 + CH4
(unbalanced equation)

Olivine, carbon dioxide and water go in – serpentine, magnetite (a form of iron oxide) and methane come out. The constraints on this mechanism on Mars would be the lack of any obvious geologic activity. Mars’s tectonics seem to have long since seized up, leaving the quesion of how enough olivine would come into contact with enough water to cause the huge amounts of methane seen. Without any geological activity to sustain the reaction, all olivine surfaces would eventually become coated in serpentine. It’s a self-limiting process. If this is the source of the martian methane, it would mean that Mars isn’t geologically dead after all, which would be quite a revelation in itself.

Methane Clathrate

Another possibility would be methane clathrate. Found on some of Earth’s ocean floors as well as several icy moons, it’s a form of ice with methane molecules trapped inside it. Melting this clathrate could cause a release of methane. Any stray non-melted clathrate would float to the surface (it’s still ice, after all), and/or the water would seep away. This would allow more clathrate to be exposed to the surface, replenishing the supply.

The big news in this is simple: if seasonal warming can cause subsurface clathrate to melt, then there could well be liquid water somewhere beneath the surface of Mars.

I should note that this mechanism is my own inference. There could be a good reason I don’t know about why this isn’t possible — though I can’t think of one. Mind you, I have no idea how long such a reservoir of methane might last.

Methanogens and Methanotrophs

Potentially the greatest revelation in this discovery — could the methane be produced by martian life? On Earth, methanogenic bacteria live in places without free oxygen, like swamps and cows’ stomachs. You can probably guess from the name that their biochemistry means they create methane. The idea put forward by NASA scientists uses carbon dioxide and hydrogen;

CO2 + H2 → CH4 + H2O
(unbalanced equation)

This is a method used by, among other things, subsurface microbes on Earth. Buried beneath Africa, radioactive minerals split water molecules into oxygen and hydrogen. Methanogenic microbes there use that hydrogen to create methane this way, existing without even needing sunlight (a different kind of microbe, incidentally, to the ones I’ve written about previously). The idea seems decidedly plausible.

Another thing that falls out of this idea is that if methanogenic microbes exist, then another type of microbe may exist, called “methanotrophs”. Methanotrophs use the opposite reaction, effectively breathing in the methane and exhaling CO2. Even though they aren’t fully understood, microbes like these also exist on Earth’s ocean floors, using the methane there because there isn’t enough free oxygen available. Anaerobic respiration, in other words. A bloom of methanotrophs on Mars could conceivably explain the rapid dissappearance of the martian methane clouds. In effect, there could be an entire ecology around Mars’s equator, based around methane.

So we could well be looking at the first good evidence of life on another planet (ignoring a certain meteorite). That’s just a huge concept. Mindblowing, in fact.

Genuinely, there’s no overwhelming reason why any one of these three ideas is less likely than the others; at least based on what we currently know. Interestingly, some of the plumes contain water vapour, while some don’t. I really don’t know what to make of that fact…

I do know one thing, though — I can’t wait for NASA to release more data on this!


In case you’d like to read it: The NASA Press Release.

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
This entry was posted in astrobiology, chemistry, Imported from Livejournal and tagged , . Bookmark the permalink.

19 Responses to The Mystery of the Martian Methane

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  5. invaderxan says:

    Re: photoreduction can form methane
    Oh, now that’s interesting… photoreduction is a process I hadn’t considered!
    Thinking about this rationally, methane production is highest when solar irradiance is at a maximum — but why would it be concentrated around three spots just north of the equator?
    Mars’s atmosphere is known to contain traces of water vapour. Large amounts of it are transported through the atmosphere seasonally, and clouds of ice crystals have been observed by the Mars rovers. For some reason, this doesn’t cause such photoreduction on a global scale. The process seems restricted to specific areas. Moreover, if photoreduction is the culprit, surely the seasonal frosts in the Martian polar regions should be accompanied by some amount of methane release.
    The implication would be that either there’s a large concentration of subsurface water (liquid or frozen) beneath the surface at those three points, or that for some reason those three places are the only places where suitable catalysts can be found in sufficient quantities. The latter seems unlikely, in my opinion — although being as the region was previously volcanic, there could be an enhanced abundance of sulfides present.
    Seasonal heating could certainly cause a release of water vapour, however, which could undergo photoreduction when it reached the surface. The question then would be why one of the three main plumes contains no traces of water vapour. Could the catalytic activity be significantly higher in this area for some reason?
    As a hypothesis, this isn’t without its problems, but I definitely agree that it’s a mechanism that should be strongly considered. I’ll have a look for a couple of papers to read when I have a chance — can you recommend any specific authors?
    By the by, whether or not the process is prevalent on Mars, it certainly has some implications for icy mantles on interstellar dust grains (which is another interest of mine) — so thank you very much for pointing it out! :)

  6. invaderxan says:

    Re: Plasma life
    LOL! Oh man, I’d forgotten all about that — that was pure genius!

  7. Anonymous says:

    photoreduction can form methane
    You know, there a few dozen chemistry journal references on photoreductive processes to form methane from CO2 and H2O (or H2), over metal oxide or metal sufide catalysts. I suggest the Martian methane may be nothing more than a photoreductive process. After all, methane production is highest where there is maximum solar irradiance, and humidity…exactly as one would expect if the mechanism were photoreduction.
    These chemistry papers were done in a flask, but I think this mechanism should be explored for Martian condifitons.

  8. Anonymous says:

    Re: Plasma life
    Hydrogen monoxide is what I’ve heard authoritatively by a pedantic chemist. Saying it as DHMO is a redundancy. But it made such a nice Web parody and hoax… “the Dangers of DHMO”. LOL

  9. invaderxan says:

    Re: Plasma life
    Oh absolutely. It’s a fascinating idea, though I must admit, I’m not sure where such structures could both form and remain stable… The possibility alone is worth some theoretical exploration though. Sometimes it’s nice that the best sci fi authors do just that!
    As for the stuff of life, it’s worth noting that water is the third most abundant molecule in the universe, and the majority of carbon is expected (at least by people like me) to be in the form of interstellar PAH molecules. Actually, as much as I like to consider alternatives, dihydrogen monoxide (or should that be oxygen dihydride?) is pretty amazing stuff…

  10. Anonymous says:

    Plasma life
    Hi InvaderXan
    You saw that one too? I’m a Arthur Clarke, James Blish & Greg Benford fan, all of whom feature plasma life in their stories, so I’ve always been open-minded about the prospect. There’s so much of the stuff in the Universe you’d think life must’ve evolved out of it. Surely easier to find than large amounts of liquid hydrogen monoxide contaminated with hydrocarbons and solutes.

  11. invaderxan says:

    Re: the real Martians
    Reminds me of the idea of life based on plasma crystals
    Yeah, I think we’d all like it if there was even a small underground biosphere on Mars… It’s a fascinating thought!

  12. Anonymous says:

    the real Martians
    Hi InvaderXan
    I agree about the creepiness. All that desert, those marching dunes, the weird sedimentation preserved in the rocks, and parades of dust-devils criss-crossing it all. Olaf Stapledon’s “Last and First Men” featured Martians whose physical form was like a cloud, organised via electromagnetic signalling. Kind of like a dust-devil, with its electrostatic fields and peroxide making ability… ;-)
    The methane plumes are an exciting find. I’m hoping for a vast underground biosphere which usually remains sealed up, but occasionally belches out some excess…

  13. invaderxan says:

    Give it a few years, and who knows? ;)

  14. invaderxan says:

    Totally. Either way is exciting!

  15. The big news in this is simple: if seasonal warming can cause subsurface clathrate to melt, then there could well be liquid water somewhere beneath the surface of Mars.
    Can’t wait to see it on Man vs Wild

  16. ryttu3k says:

    I’ve been following this one. It’s making me all tingly and happy XD And hey! Either geology OR astrobiology would make me happy XD

  17. invaderxan says:

    Good point!
    Where methane on Mars would have come from in the past is a whole different story. There would be some amount trapped inside the planet from back when it formed too, and how much methane could be accounted for by outgassing is something I have no clue about. I’m no expert. :)
    The methane could also originate from some kind of martian oil field, I suppose…

  18. stargzr_htn says:

    If it’s methane clathrate, the methane would still have had to be produced in the past, to become entrapped. No?

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