https://www.scientificamerican.com/article/mars-scientists-edge-closer-to-solving-methane-mystery/

Planetary scientists are getting closer to solving the puzzle of methane on Mars.

New calculations could help to explain why NASA’s Curiosity rover detects peaks of methane gas in the Martian atmosphere during the planet's northern summer. As winter gives way to spring, the idea goes, the Sun’s heat begins to warm the soil—allowing methane to percolate up from the ground and into the atmosphere, said John Moores, a planetary scientist at York University in Toronto, Canada. He presented the work at a planetary-sciences meeting on October 24.