A pair of papers just out show a mysterious absence of acetylene on Saturn’s moon Titan.
Combined with a net flux of molecular hydrogen to the surface, this provides a tantalizing hint that there might be biochemistry taking place, with methane as the working fluid and hydrogen and acetylene as the primary energy source in a reductive metabolism.

Such a metabolic cycle was suggested five years ago by Chris McKay at NASA Ames.
The data, from NASA’s Cassini Mission shows two hints of peculiarities.

C2H2 – acetylene is missing from the mix of nitrogen, methane and hydrocarbons seen in Titan’s atmosphere. Acetylene should be produced in the atmosphere through chemical reactions, and rain down to the surface, but no acetylene is detected on the surface. Suggesting that the acetylene is being consumed on the surface through some reaction.

Further, molecular hydrogen, H2, is generated in the upper atmosphere through ultraviolet photolysis of methane, CH4 – the hydrogen escapes to space, its molecular weight is light enough, that the tail end of the most rapidly moving hydrogen molecules can escape Titan’s gravitational field – but the vertical density gradient of hydrogen in Titan’s atmosphere suggest a net flux of H2 down to the surface, in an amount comparable to that escaping to space.

One explanation, is that there is life on Titan, doing anaerobic biochemistry powered by sunlight – through the intermediate path of photolysis of methane to hydrogen, and involving the consumption of acetylene.



Methane lake on Titan – artist’s conception

Anaerobic methanogenesis is known on Earth, and is a viable metabolic cycle, though on Earth water is the working fluid.
This would use liquid methane as the working fluid, and be qualitatively different from Earth life.

IF confirmed, this would be an astonishing breakthrough.
It is quite possible, that the process is instead some inorganic catalytic chemical process that consumes the hydrogen, and also converts the acetylene.
There is no known inorganic mineral catalyst that could do this, but then we don’t exactly have comprehensive understanding of hydrocarbon chemistry in these conditions.

We’re talking a fair amount of stuff – the effective energy flux is about 0.1% of that at Earths surface the energy flux is diluted both by distance, and the limitation on using just the UV portion of the spectrum.
That could still support a respectable biosphere.
The H2 flux is about 1028 atoms per second, or about 10 kg per second – that is close to a megaton per year, in round numbers.

Hm, archaean bacteria mass ~ 10-12 gm, and there are something like 105 metabolic driver molecules per cell. So… if we assume a slow metabolism, plausible given the temperatures and energy fluxes, we might guess each driver molecule cycles maybe 10 times per second.
This would require a million hydrogen atoms per organism per second, or a total of 1022 organisms for the whole moon, or about 100 million per square meter.
10,000 per square centimeter, on average.

Yeah, that works.

This is a potentially very interesting line of investigation.
It is very premature to make any announcements about alien life from this, but, I’m not an author and this is a blog, so I can go a little bit wild on this: the key aspects of this result were predicted, and predicted to be positive indicators for life, qualitatively different, alien life.
This is not definitive by any means, but tantalizing, and something to keep an eye on.

So, er, give NASA shitloads more money to do some Icy Moon Astrobiology!

Unfortunately, if BP doesn’t get its act together soon, this will leave the Southeastern USA a ripe target for alien invasion, as the Titanic hordes react to the heat bombing of their moon by the Huygens probe…

JPL Press Release

Of course no one will read the papers, since planetary scientists don’t believe in arXiv…

ADS pointer to McKay and Smith 2005 paper

Don’t have the new papers. Yet.
(Hint – send me a pdf or link if you got a copy).

Comments

  1. #1 AJ Milne
    June 23, 2010

    Very much agreed, and re the research direction in general, not just on this particular body…

    As in: given the rate at which we’re adding exoplanets to the catalogues, and the rate of progress in instrumentation and techniques, I think it’s safe to say we’ll be getting spectra off of an awful lot more bodies besides Titan in not much longer, and some of those, too, are going to present some interesting puzzles like this one–puzzles well worth assessing with a little more focus on such possibilities as microbial (or larger) life.

    SETI gets at lot of attention when you start talking about what’s out there, but just from what we know of our own planet, you could have looked at it over a period of billions of years–by far most of the time it’s been here–and while SETI-type stuff would have seen nothing (because there were no radio transmitters except in the last blink of an eye in geologic time), there would have been a lot of interesting stuff to see in the atmosphere–signatures of life doing what life does to gas mixtures.

    So I think we should be thinking hard about how we spot that with (very) remote sensing. It’s a field in waiting, if ever there was one. And here’s to more money for–and emphasis on SETL–the search for extraterrestrial life not necessarily interested in or even remotely capable of contacting us. Even if it’s not quite so dramatic as a Contact-style transmission, a spectrum revealing the presence of life moving oxygen or other electron acceptors is well worth spotting.

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