Methane on Mars: Seasonal Gas Leaking from a Buried Reservoir

In June 2019, the Curiosity rover measured a methane spike of about 21 parts per billion in Gale Crater. The usual background was much lower. The gas fell again days or weeks later, and Curiosity recorded other short increases. The ExoMars Trace Gas Orbiter, looking from above at a broad column of atmosphere, did not see methane at a comparable level.

One instrument saw gas near the ground. Another did not see it from orbit. Both results can stand together if methane sits in small pockets beneath the soil, escapes in a season, and is held back by soil, salts, or radiation before it spreads. If microbes make the gas, those pockets could be places where life survives. If rock and water make it, Mars still has active chemistry.