[X] My Assistant

[Bill Thompson]

What is the latest on the origins or the existence of methane on Mars? Have there been any new thoughts or information.

This is my very first post here so I do not know who visits this forum and how current the information is.

[Guest_BruceMoomaw_*]

Yes, they very definitely are. There have also been a few relevant recent abstracts.

(1) From the upcoming COSPAR meeting ( http://www.cosis.net/abstracts/COSPAR2006/...e2f32646b163e72 0;

T. Encrenaz: "The detection of methane on Mars has been reported by several teams, in some cases tentatively, using both space and ground-based measurements. Krasnopolsky et al. (Icarus 172, 537, 2004) reported a mean CH4 mixing ratio of 10 ppb, from groundbased near-IR measurements. Using PFS aboard Mars Express, Formisano et al. (Science 306, 1756, 2004) announced possible variations over the disk with a maximum mixing ratio of 35 ppb. From high-resolution imaging spectroscopy, Mumma et al. (BAAS 36, 1127, 2004) reported the detection of localized hot spots with maxima as high as 250 ppb. These hot spots however were not confirmed by further PFS observations (Encrenaz, AGU, December 2005), which might imply a temporal evolution of these features. This talk will review recent observations devoted to the search for methane, and will discuss possible interpretation and further work."

Encrenaz also delivred a talk on this at December's American Geophysical Union meeting -- which I attended. At that talk, he specified that the Mars Express team now believes the overall range of methane they're seeing at different places on Mars to vary between 0 and 25 parts per billion rather than 35 parts; but they still see an average amount of 10 ppb. He remains puzzled by Mumma's ground-based detection of much higher local levels -- but he says that he personally finds Mumma's data "rather convincing", and wonders whether it may indicate dramatic changes over time. (Mumma's observations were made in March 2003.) He also totally retracted the team's earlier statement that they had also seen evidence of tiny traces of formaldehyde in Mars' air (which, if it existed, could have been made simply by the nonbiological oxidation of methane in the air).

(2) Carl Allen had an abstract at the latest LPSC meeting ( http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1193.pdf ) on his recent photographic observations of Arabia Terra, one of the three regions which seem to have the highest concentrations of methane -- and which was already noted for having the highest concentration of near-surface water in some form (ground ice and/or hydrated salts) to be found anywhere near mars' equator, according to Mars Odyssey. This is clearly a very interesting region -- it also shows large numbers of layered outcrops, suggesting that it may be "an ancient sedimentary bed" -- but another paper concluded that the various mineral compositional instruments in orbit around Mars right now haven't seen anything unusual there in that particular respect. Clearly, however, it's worthy of much more study.

(3) There is still a lot of dispute over possible sources for the methane, either biological or nonbiological. One possible source -- a recent comet impact -- now seems to be ruled out as not containing enough of the stuff. But there's still a good chance that it comes either from volcanic venting or from "serpentinization" (the reaction of the mineral olivine, which exists in large amounts on Mars, with water, releasing hydrogen which in turn could react with small amounts of carbon in Mars' rocks to form methane). Another AGU talk by J. R. Lyons ( http://www.agu.org/cgi-bin/SFgate/SFgate?&...t;P53A-04" ) discussed this in more detail, but unfortunately I missed that talk.

(4) There is also the real possibility that it's being made by still-living underground Martian bacteria -- "methanogens" -- and some such bacteria have been discovered under Earth's surface, most recently in the strange sulfur-rich environment of Spain's Rio Tinto ( http://www.agu.org/cgi-bin/SFgate/SFgate?&...t;P42B-02" ).

At this point, any further actual data on Martian methane will have to come for the next few years from more observations either by Mars Express or ground-baed telescopes -- the Mars Reconaissance Orbiter isn't equipped to look for it. However, the 2007 Phoenix lander has some ability to detect it, and the 2009 Mars Science Lab should be able to do an extremely sensitive check for it -- including determining its isotopic ratios, which could give us more information on whether it's likely to be produced by living germs or nonliving processes.