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Mars, methane on
Methane gas has been detected in the atmosphere of Mars by three separate groups of researchers. Because methane is unstable in the Martian atmosphere, with a lifetime of just a few hundred years, it appears that some process on or below the surface is continuously replacing the gas. The two likeliest possibilities were thought to be volcanic activity and methane-producing microbes (see methanogens). However, research published in 2005 appeared to rule out volcanoes as a source of the methane having failed to find any sulfur dioxide in the Martian atmosphere.
Methane was detected by the Fourier Transform Spectrometer aboard the European Mars Express orbiter, a team from NASA Goddard Space Flight Center using several large telescopes, and a team led by Vladimir Krasnopolsky using the Canada-France-Hawaii Telescope. All three suggest a methane abundance of 10-11 parts per billion. Interestingly, the NASA team has produced a map that shows a concentration in the equatorial region, which includes Meridiani Planum, currently being explored by the Opportunity rover. Opportunity has found almost conclusive evidence that this region was once inundated with saltwater.
Although a biogenic explanation is one strong possibility, scientists are urging caution when interpreting the results, saying that the instruments looking for chemical signatures in the Martian atmosphere are not yet good enough to conclusively detect methane. Even if methane exists on Mars, the gas could be a product of non-biological processes such as active volcanoes.
In mid-March 2004, the European Space Agency announced that a team led by Vittorio Formisano of the Institute of Physics and Interplanetary Science in Rome had detected methane in the Martian atmosphere using the PFS aboard Mars Express. This instrument maps the infrared radiation from the Martian environment in wavelengths from 1.2 to 50 microns. The researchers averaged data from nearly 1700 spectral samples taken by Mars Express in January and February 2004 and found a line at exactly the point (3.3 microns) where one would be if methane were present in the Martian atmosphere. "We have been able to detect a very small quantity of methane," says Formisano. "It's around 10.5 parts per billion." The result confirms data collected by the NASA team led by Michael Mumma, reported at the annual meeting of Division for Planetary Sciences in September in 2003. Mumma's group detected one spectral line for methane on Mars using highly sensitive infrared spectrometers attached to the Gemini South telescope on Cerro Pachon, Chile, and the Keck-II telescope on Mauna Kea, Hawaii. According to Mumma, the resolution of the ground-based telescopes used by his group was 50 times greater than instruments on Mars Express. Both these results are supported by yet another group. Vladimir Krasnopolsky of the Catholic University of America in Washington DC and his colleagues have also found a single spectral line for methane on Mars using the Canada-France-Hawaii telescope. They will be presenting their results at the European Geophysical Union's meeting in Nice, France in April.
The three reports are fuelling speculation about where the methane comes from, although more confirmation is needed. Methane in the Martian atmosphere is not stable and cannot last more than a few hundred years, because it reacts with hydroxyl ions in the presence of sunlight, forming water and carbon dioxide. On Earth much of the atmospheric methane is produced by methanogenic bacteria that digest organic matter in areas such as wetlands and waste landfills, and even in the guts of some animals and produce methane as a by-product. There is also methane beneath the Earth's crust that is left over from the formation of hydrocarbons. This old methane is routinely spewed out of mud volcanoes, vents, and bubbling pools, or it slowly seeps out of fissures in Earth's crust. Methane can also be formed during volcanic eruptions and in geothermal reservoirs. Formisano's team is now trying to determine variations in concentrations of methane in the Martian atmosphere to pin down any obvious sources.
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Frozen sea on Mars linked to elevated methane (Feb 25, 2005)
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