[InABunkerUnderSF]

The molecules mentioned in the corresponding NASA/JPL release, in addition to methane, are "thiophenes, benzene, toluene, and small carbon chains, such as propane or butene".

Could be cows but my guess is volcanoes.

[Future Snake Eater]

It sounds to my highly untrained ears that they’re going along the biological “fossil fuels” theory of the development of this stuff. Isn’t that still an unproven, somewhat controversial theory in nerd circles?

[Hootowl99]

I suspect crude oil...