One of the most puzzling and controversial discoveries made about Mars so far has been the detection of methane in its atmosphere. Why is this significant?
On Earth, most of the methane in the atmosphere comes from two sources: biology and volcanic activity, with biology being predominant by far (about 95%). So if methane is present in Mars’ atmosphere in significant amounts, as has been suggested already by both the Mars Express orbiter and Earth-based telescopes, its origin is likely to be similar.
The methane seems to be fairly localized to three main regions in the northern hemisphere of the planet, in the form of large “plumes,” instead of just random. These are also areas which show evidence of previous ice and water.
According to Dr. Michael Mumma of NASA’s Goddard Space Flight Center, “Methane is quickly destroyed in the Martian atmosphere in a variety of ways, so our discovery of substantial plumes of methane in the northern hemisphere of Mars in 2003 indicates some ongoing process is releasing the gas. At northern mid-summer, methane is released at a rate comparable to that of the massive hydrocarbon seep at Coal Oil Point in Santa Barbara, Calif.”
He adds, “Right now, we don’t have enough information to tell if biology or geology – or both – is producing the methane on Mars. But it does tell us that the planet is still alive, at least in a geologic sense. It’s as if Mars is challenging us, saying, hey, find out what this means.”
There also appear to be seasonal variations in the amount of methane seen during different times of a Martian year. This implies that the production of methane is somehow connected to the changing seasons, with the plumes peaking during spring and summer.
These observations would most easily be explained by either geological activity or biology. One problem though is that so far there have been no signs of current volcanic activity, which does produce small amounts of methane on Earth. All of Mars’ volcanoes are thought to be long extinct. Small amounts of residual activity deep underground are not impossible, but so far have not been detected. Methane could also be trapped in underground ice deposits called clathrates.
It may also be produced by a process called serpentization, where iron oxide (rust) is converted to serpentine minerals by a combination of water, carbon dioxide and heat (also underground), producing methane.
If biology, it would most likely be microbial and underground given the harsh surface conditions. It could even be reservoirs of methane left over from previously living microbes which is locked in the ground.
Meteorites could also deliver trace amounts of methane to the surface, created by the action of ultraviolet light on organic molecules in them, but the total amount possible by this scenario, possibly less than one part per billion, is far below what has been observed and it would not produce regular seasonal variations.
It should also be noted that while the gas and ice giant planets contain methane in their atmospheres, in those cases it a primordial form of methane thought to be left over from their formation, and is not the same as methane produced primarily by active geology or biology on small rocky planets like Earth or Mars.
The Curiosity rover may be able to help answer this provocative question. The Sample Analysis at Mars (SAM) instrument onboard is able to detect any methane present in the atmosphere, and more accurately than has been possible so far.
Interestingly, there has been some speculation about this in recent weeks. Since Curiosity landed in early August, it has taken several measurements of the atmosphere for analysis, although no results have been released yet. When asked about this in the weekly press briefings, the response has been that the tests are still on-going, with a need for analysis from multiple observations. During last week’s briefing, it was mentioned that some results might available within a month or so.
This has some people wondering if methane has tentatively been found already. If none has been found but only the other “normal” gases known to be present in the Martian atmosphere, which would hardly be surprising, then why the need to do repeated testing without acknowledging this yet?
As mentioned to Space.com by astrobiologist Dirk Schulze-Makuch of Washington State University, “Methane is really quite a rare gas in hydrothermal / volcanic exhalations; thus a methane detection with the rover would be exciting and could point to biology, especially if detected in relatively large amounts.”
He continues, “Even more exciting, would be if the carbon in the methane has an isotopic fractionation that is consistent with biology. If the methane is produced by organisms – for example, metabolism – then we expect a shift to the lighter isotopes. In essence because life is lazy, same effect, with less work compared to inorganically produced carbon.”
If the methane has been detected, as is being rumoured (just rumours right now), then the need for repeated testing to confirm this would be absolutely necessary. In the meantime, it is a case of “wait and see” but hopefully we will know more soon.
This article was first published on Examiner.com.