Seems this comes from either:

1) Volcanoes 2) Methanogen microbes

Since no active volcanoes are around, the article posits the more likely explanation is the microbe one. Not sure the half life on methane. Could this methane be lingering from whenever volcanoes were last active? If so, the more parsimonious explanation is the volcano one. If the half-life of methane is too fast for the methane detected to be left-over methane from ancient volcanoes, and if further we are quite certain there are no active volcanoes there now, then perhaps the most parsimonious explanation for the methane would be methanogens living beneath underground ice. If we can rule out the volcano theory, then the next step would be to send Bruce Willis over there to drill for methane and the methanogens that produced it.