Atmospheric methane on a terrestrial planet would be a biomarker. Bio-suggestion maybe. Free methane in the atmosphere of a planet anywhere near the habitable z

Atmospheric methane on a terrestrial planet would be a biomarker. Bio-suggestion maybe. Free methane in the atmosphere of a planet anywhere near the habitable zone of a star would be readily broken down. If there's a good amount detected it suggests replenishment by biological processes. Biological processes are definitely not the only source of methane. It's enough to warrant more observations or even new instruments.