Mumma's methane

At the September meeting of the American Astronomical Society's Division of Planetary Science, which is rather pleasingly in Cambridge this year, Mike Mumma will be presenting some very interesting sounding methane data. The abstract is here. The key idea is that the rate of methane production is a great deal higher than calculations based on the theoretical atmospheric lifetime would suggest

Our differential extractions for methane implied strong latitudinal gradients - these are contrary to predictions if photochemistry limits the lifetime of methane on Mars, but instead require local release and a much shorter lifetime. The lifetime against destruction cannot be much longer than equator-to-pole transport times imposed by the Hadley circulation (weeks). A shorter lifetime requires that estimated production rates be revised upwards commensurately.

If the methane had a long lifetime, it would be spread evenly across the face of the planet. It doesn't, so it has a short lifetime (possibly because of catalysed interactions with surface oxidants, or oxidants on dust). And for a given total amount of atmospheric methane a shorter liftime means a higher rate of production. The 2,000 cows have reinforcements.

Neither the absolute rate or the implication that production must be regional in themselves argue for or against biological production. Geothermal sources are regional too (though if the rate is really high, you'd have to wonder why the hotspot doesn't show up in the infrared). Sushil Atreya will be looking into some of the possibilities at the same session of the meeting. Interestingly, Atreya's abstract suggests that some of Mumma's data show a significantly higher level than PFS or the Krasnopolsky team reported.

Also interestingly the Mars Express PFS team (of which Atreya is a member) has no abstracts at the meeting reporting any more methane data, or indeed any trace gas data at all. That said Vittorio Formisano is part of the team reporting on Cassini's intriguing bright spot on Titan.

I'm looking forward to September 6th quite a lot right now.

For anyone needing a refresher, the summary from the end of last year's methane excitement on this blog is here, and the most recent take on the PFS work was here. (And if anyone knows why some of my archives seem to be in a strange blue format, I'd be grateful for the info). There's been a recent series of articles on astrobio.net, including this one on possible methane sources.

Comments

[marrije]

I'm afraid I don't see any 'strange blue formats' on the archives. Everything seems in perfect working order from where I'm looking. Perhaps there was a small local stylesheets hickup at your place?

[Alex R. Blackwell]

I'm not sure if it has mentioned here or not, but the MEx PFS team recently published a series of papers in Planetary and Space Science (Volume 53, Issue 10, pp. 959-1095, August 2005), which is a special issue entitled "First Results of the Planetary Fourier Spectrometer aboard the the Mars Express Mission."

See http://makeashorterlink.com/?F2B16268B