Methane gas is periodically detected in the atmosphere of Mars. This was once considered implausible and perplexing, but it is now widely accepted by planetary scientists. Why the methane is there is still a mystery. It could point to present-day Martian microbes living in the rocks below the surface.
Scientists working with the ESA’s Mars Express orbiter reported that in the summer of 2013, the spacecraft detected methane within Gale Crater, a 96-mile-wide depression near the Martian equator.
In the same summer of 2013, NASA’s Curiosity rover also measured a marked rise of methane in the air that lasted over two months.
The presence of methane is significant because the gas decays quickly. Calculations indicate that sunlight and chemical reactions in the thin Martian atmosphere would break up the molecules within a few hundred years, so any methane detected must have been created recently.
It could have been created by a geological process known as serpentinization, which requires both heat and liquid water. Or it could be a product of life, specifically methanogens, microbes that release methane as a waste product. Methanogens thrive in places lacking oxygen, such as rocks deep underground and the digestive tracts of animals.
Even if the source of the methane turns out to be geological, the hydrothermal systems that produce the emissions would still be prime locations to search for signs of life.
A newer European Mars spacecraft, the Trace Gas Orbiter, which has a more sophisticated methane detector, has been in orbit since 2017, but no results have been reported as of yet.