On Earth, methane is produced mainly by life, and it has been proposed that, under certain conditions, methane detected in an exoplanetary spectrum may be considered a biosignature. Here, we estimate how much methane may be produced in hydrothermal vent systems by serpentinization, its main geological source, using the kinetic properties of the main reactions involved in methane production by serpentinization. Hydrogen production by serpentinization was calculated as a function of the available FeO in the crust, given the current spreading rates. Carbon dioxide is the limiting reactant for methane formation because it is highly depleted in aqueous form in hydrothermal vent systems. We estimated maximum CH 4 surface fluxes of 6.8 · 10 8 and 1.3 · 10 9 molecules cm -2 s -1 for rocky planets with 1 and 5 M 4 , respectively. Using a 1-D photochemical model, we simulated atmospheres with volume mixing ratios of 0.03 and 0.1 CO 2 to calculate atmospheric methane concentrations for the maximum production of this compound by serpentinization. The resulting abundances were 2.5 and 2.1 ppmv for 1 M 4 planets and 4.1 and 3.7 ppmv for 5 M 4 planets. Therefore, low atmospheric concentrations of methane may be produced by serpentinization. For habitable planets around Sun-like stars with N 2 -CO 2 atmospheres, methane concentrations larger than 10 ppmv may indicate the presence of life.

This paper reviews the distribution of methane (CH 4 ) in our Solar System, as well as its sources and sinks in the atmospheres of the main Solar System bodies. Methane is widely distributed in the Solar System. In general, the inner planets are methane-poor, being Earth a unique exception, whereas the outer planets have CH 4 -rich atmospheres. In general, the atmospheric chemistry of this compound is dominated by the solar radiation although in O 2 -rich atmospheres this compound participates in a reaction system that removes atmospheric CH 4 . In our planet most of the atmospheric CH 4 is produced by lifeforms, reason why scientists have proposed that the simultaneous detection of methane signal along with oxygen (O 2 ) or ozone (O 3 ) signals in the atmospheric spectra of planets may be good evidence of life. Therefore, the study of this gas at planetary level is important for understanding the chemical reactions that control its abundance on the exoplanetary atmospheres and to classify possible inhabited planets.Keywords: methane, biosignatures, Solar System. Resumen El objetivo del este trabajo es hacer una revisión sobre la distribución del metano (CH 4 ) dentro del Sistema