Lake beds. River channels. Mountains and valleys. Mars is a planet that has liquid water, and now organic materials. Both are key ingredients to life as we know it. Now the detection of methane coming from an ancient lake bed continues to point us in the same direction - organic matter producing organic compounds.
CH4 - The lightest and simplest hydrocarbon fuel. Methane is produced by bacteria from decaying organic matter, like when you get a waft of a septic tank. That is also a hallmark of biological processes of life, and thus methane is especially sought-after when looking for life elsewhere in the universe.
That isn't to say that there aren't any abiogenic pathways to producing methane gas. One proposed reaction involves olivine, a green mineral with carbon dioxide and water. If there's enough water under the surface and there's olivine, it could produce methane to some extent.
However could it be that our earth-sized cousin has bacteria or other life forms underneath the harsh surface, where there could be access to liquid water? It's not a hypothesis that's really "far out of this world" if you ask me.
