https://www.scientificamerican.com/article/mars-has-methane-but-does-it-have-life/

We may be one step closer to cracking the Mars methane mystery.

NASA’s Curiosity rover mission recently determined that background levels of methane in Mars’ atmosphere cycle seasonally, peaking in the northern summer. The six-wheeled robot has also detected two surges to date of the gas inside the Red Planet’s 96-mile-wide (154 kilometers) Gale Crater—once in June 2013, and then again in late 2013 through early 2014.