Methane on Mars

Methane may be an invisible gas, but that doesn’t mean you can ignore it. Here on Earth, it’s both a valuable resource (it’s the major constituent of natural gas) and a contributor to global warming (molecule for molecule, methane traps more than 20 times more heat than carbon dioxide). Now it appears it may also exist in the Martian atmosphere–and if that holds up, then methane is about to make big headlines, as the best evidence to date that there is life on the Red Planet.

The story of methane on Mars is just now starting to bubble to the surface, even though the first evidence of it was presented back in the fall. That’s because there are now three independent groups of scientists reporting that they’ve found methane in the Martian atmosphere.

Most recently, a European Space Agency team, led by Vittorio Fromisano of the Institute of Physics and Interplanetary Science in Rome, announced that it has detected methane in the Martian atmosphere using the Planetary Fourier Spectrometer aboard the ESA’s Mars Express spacecraft, currently orbiting Mars. The spectrometer maps infrared radiation from the planet across a range of wavelengths. Elements in the atmosphere each absorb radiation at a characteristic wavelength, leaving dark lines in the spectra. The team averaged data from nearly 1700 samples taken in January and February, and found a line exactly where it should be for methane. Based on their results, they put the quantity of methane at about 10.5 parts per billion.

(By way of contrast, the current level in Earth’s atmosphere is 1.72 parts per million. That’s twice the two-centuries-ago level of 0.8 parts per million; 70 to 80 percent of current methane emissions on Earth are thought to be caused by human-related activities.)

The ESA team’s findings confirmed a finding of methane on Mars reported in September by a team led by Michael Mumma of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. His team used infrared spectrometers on the Gemini South telescope, located on a mountaintop in Chile, and the Keck-II telescope on the summit of the extinct Mauna Kea volcano in Hawaii.

A third group, led by Vladimir Krasnopolsky of the Catholic University of America in Washington, D.C., will be presenting its finding of a spectral line for methane in the Martian atmosphere at a conference in France in April. There’s a Canadian connection to this upcoming report: the group used the Canada-France-Hawaii telescope, a 3.6-metre optical infrared telescope, also located on Mauna Kea, jointly operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique of France and the University of Hawaii.

Why is the discovery of methane on Mars exciting? Because methane is not stable in the Martian atmosphere–it can’t last there more than a few hundred years; the intense ultraviolet radiation from the sun causes it to react hydroxyl ions forming water and carbon dioxide. That means there must either have been a very recent source of methane on the planet–or there’s an ongoing source.

One possible source is volcanic activity. However, so far no volcanic hotspots have been detected on the planet by any of the orbiting space probes. Volcanic activity would be a major discovery because Mars has a lot of water locked up as underground ice. Volcanic heat could mean underground water, an excellent habitat for life.

But the other possibility is even more sensational. Most of the methane in Earth’s atmosphere comes from bacteria, which digest organic matter in places like swamps, rice paddies and landfills–and the guts of many animals–producing methane as a by-product. These bacteria, called anaerobic, do not need oxygen to survive. Anaerobic bacteria were probably the first forms of life to appear on Earth, and therefore are likely candidates to be the first forms of life to have appeared on Mars, back when it had more liquid water (as the Mars Rovers have indicated was the case).

In other words, the methane being detected in the Martian atmosphere could be the gassy breath of bacteria that evolved in Mars’s ancient salty seas, and that have managed to cling to life in whatever pockets of briny water still exist in the Martian soil.

The Rovers are primarily geological explorers, not equipped to search for life, or methane–but you can bet future missions will be.

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