Another idea about Mars methane
Yet another possible explanation has been suggested for the methane that three different groups say they have detected in the Martian atmosphere. And as a bonus, the new hypothesis also could explain some unusual formations seen in the Meridiani Planum region, which the rover Opportunity has been studying.
Dorothy Oehler, a geologist at NASA's Johnson Space Center, suggests that kerogen, the tarry, compressed and altered remains of ancient organisms that on Earth, compressed under miles of rock, is the source material of petroleum and natural gas, could also be present deep below the Martian surface and be producing a steady seepage of methane that may have been ongoing throughout Martian history.
Oehler, who presented the idea at the annual meeting of the Lunar and Planetary Science Conference in Houston, Texas, was careful to emphasize that she is not suggesting that there is any strong evidence for the existence of kerogen on Mars, but is simply offering another alternative to add to the list of previously suggested mechanisms that might account for methane production: volcanism, meteoritic impacts, the decay of recently-living organisms, or the metabolism of microbial life on Mars today.
On Earth, about half of all the methane that is naturally in the atmosphere (not counting contributions from human activity) comes from the breakdown of kerogen deep below the surface, Oehler said. The other half comes from organisms, either through their metabolic activity or their decomposition.
In places where there are large kerogen formations, methane continually seeps upward, as a result of the breakdown of the kerogen through geothermal heating. In the process, the highly reactive methane alters many of the minerals that it percolates through, and often leaves a telltale signature at the surface in the form of large rings of lighter-colored altered rock.
Oehler, who formerly worked in the petroleum industry, has studied extensively one such formation, at Ashland Field, Oklahoma, a rich natural gas-producing region. There, bright rings of carbonates, known as "red bed bleaching," are produced by interaction of the methane with sands made mostly of reddish iron oxides such as hematite. In various places, methane seeps on Earth produce rings of pyrites, sulfur-rich evaporites, or jarosite, all of which have now been found at Meridiani.
The ring formations are very similar in appearance to some bright rings seen at the Meridiani site from orbital imagery. Although interpreted as heavily weathered craters, they differ in many ways from other craters in the area. For one thing, they appear to be perfectly flat, with no relief to cast shadows. Spectral analysis might help to confirm the theory, if the bright rings are found to be made of such minerals.
Oehler suggests that if her idea turns out to be right, such formations could be useful indicators of possible sources of methane as fuel for future Mars missions, and possibly a good place to look for fossilized remains of past Martian life, since kerogen on Earth is often rich in microfossils.