Follow the methane: the search for a deep biosphere, and the case for sampling serpentinites, on Mars

If life occurs elsewhere in the Solar System, there is a strong likelihood that it occurs in a deep biosphere beneath the planetary surface. The evidence for methane in the martian atmosphere has drawn attention to the possible role of serpentinites in fuelling a deep biosphere through the generation of hydrogen and/or methane. Serpentinites represent a good target for the search for biosignatures in a range of reaction products. Isotopic measurements in each of methane, sulphide and carbonate in serpentinites can help determine evidence of biological activity. We show that ancient terrestrial serpentinites retain methane that could be subject to the measurement of carbon and hydrogen isotopes. There is, therefore, potential to sample serpentinites on Mars and test for evidence of life in the deep geological record of Mars.