A review of the meteor shower hypothesis for methane on Mars

Abstract Trace-level methane on Mars has been reported from Earth-based, Mars orbital, and landed assets over the course of more than 30 years of sporadic observations. Martian methane appears with two different behaviors—as a background-level trace gas present in volumetric parts-per-billion (ppbv) concentration, and as episodes with some concentrations briefly rising to tens of ppbv. This chapter reviews meteor shower/outburst infall as a possible source of episodic Martian methane, as it may account for the episodic events’ timing, random occurrences, short lifetime, and trace-level abundance. Difficulties in testing the meteor shower hypothesis include the lack of data on Martian meteor shower activity, and the fact that the delivered mass of a typical meteor shower may be insufficient to explain the 2003 methane plume reported by Mumma et al. in 2009, although other factors could be involved. The hypothesis of a meteor shower source for Martian methane is a key factor in the enigma of Martian methane.