Replenishing methane on Mars

Methane in an atmosphere is something that astronomers look for as a possible sign of life. So its discovery in the atmosphere of Mars four years ago would understandably cause a bit of excitement. But there are other possibilities of what might be producing methane on Mars, so concluding the existence of life would be premature.

Nili Fossae, a methane hotspot
Nili Fossae, a methane hotspot

Things became even more interesting when it was recently discovered that methane is produced around a few hotspots around Mars, and that these pockets of methane would dissipate within just a few years without replenishment. This means that there's something around these hotspots creating a lot of methane, either biological or chemical. Surprisingly, only one hypothesis for a chemical process is being put forward, methane clathrates, which is frozen water with a high concentration of trapped methane. Even if it turns out the methane is created from such a "mundane" chemical source, it would still be exciting since methane hotspots would also be water hotspots.

The only other possibility put forward so far is that the methane is generated by microbiological life, similar to the methanogens found on our own Earth. Or the hotspots could even be small surviving colonies of methane-exhaling Martians who evolved from methanogens, in contrast to oxygen-breathing animals such as ourselves that evolved from aerobes. The latter is way too far-fetched, but it's a fun thought to contemplate ...