Formation of methane on Mars by fluid‐rock interaction in the crust

Recent spectroscopic detections of CH 4 in the atmosphere of Mars are the first definitive observations of an organic compound on that planet. The relatively short photochemical lifetime of CH 4 (∼300 years) argues for a geologically young source. We demonstrate here that low‐temperature alteration of basaltic crust by carbon‐bearing hydrothermal fluid can produce the required CH 4 flux of 1 × 10 7 moles year −1 , assuming conservative values for crustal permeability and oxygen fugacity as implied by Martian basaltic meteorites. The crustal thermal disturbance due to a single dike ∼1 × 1 × 10 km intruded during the past 10 4 years is capable of driving the alteration, if all carbon is supplied by magmatic degassing from a dike with only 50 ppm C. Atmospheric methane strongly suggests ongoing magmatism and hydrothermal alteration on Mars.