Curiosity’s failure to find this possible marker of life makes the puzzle more interesting.
In 2004 three research groups detected methane gas on Mars, both from Earth observations and from the Mars Express orbiter. The scientific community was ecstatic, because on Earth methane is most commonly seen as an end product of metabolism by methanogenic microbes. Further, methane lasts only about 400 years on Mars, due to the strong ultraviolet flux and the oxidative conditions on the surface—which suggests that the detected methane has been released very recently!
Even more stunning, the spectrometer on Mars Express showed the highest concentrations of methane over areas of high astrobiological interest, such as Nili Fossae, Arabia Terra, and Elysium Planitia. Some of these sites are associated with volcanic activity, where hydrothermal water might percolate up to provide suitable conditions for methanogenic bacteria.
Nili Fossae, a 16-mile-wide trough on Mars.
It’s also possible that the methane formed more than four billion years ago, during the Noachian time period when the climate on Mars was warmer and wetter. In that scenario, the methane might preferably be released in spring, when some of the frozen ground thaws, allowing the old methane to bubble up. But the ...