Methane on Mars: subsurface sourcing and conflicting atmospheric measurements

Abstract We address the potential for methane to exist in the subsurface of Mars, focusing on its generation, accumulation in sealed traps, and seepage to the atmosphere. We discuss two abiotic processes that could have produced subsurface methane, even if life never developed on the planet. Compared to Earth, accumulations of methane on Mars are likely to be limited, and those that are present may be better sealed by the thick and planetwide cryosphere. Releases are thus expected to be minor and episodic. We emphasize the importance of long-term, continuous monitoring of predicted release sites, as limited, episodic releases could be easy to miss. Moreover, we note that numerous scenarios of methane fluxes from terrestrial analogs may explain non-detections by the ExoMars Trace Gas Orbiter (TGO), as they can produce atmospheric concentrations below the TGO limit of detection. Our work does not negate the potential for meteoric/cometary sources of methane, but it does illustrate the strength of the case for subsurface sourcing. Finally, we provide a map of potential locations of release and discuss remaining uncertainties and a path forward.