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

Recent spectroscopic detections of CH4 in the atmosphere of Mars are the first definitive observations of an organic compound on that planet. The relatively short photochemical lifetime of CH4 ( similar to 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 CH4 flux of 1 x 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 similar to 1 x 1 x 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.