Biological potential of martian hydrothermal systems

A source of energy to power metabolism may be a limiting factor in the abundance and spatial distribution of past or extant life on Mars. Although a global average of chemical energy available for microbial metabolism and biomass production on Mars has been estimated previously, issues of how the energy is distributed and which particular environments have the greatest potential to support life remain unresolved. We address these issues using geochemical models to evaluate the amounts of chemical energy available in one potential biological environment, martian hydrothermal systems. In these models, host rock compositions are based upon the compositions of martian meteorites, which are reacted at high temperature with one of three groundwater compositions. For each model, the values for Gibbs energy of reactions that are important for terrestrial chemosynthetic organisms and likely representative for putative martian microbes are calculated. Our results indicate that substantial amounts of chemical energy may be available in these systems, depending most sensitively upon the composition of the host rock. From the standpoint of sources of metabolic energy, it is likely that suitable environments exist to support martian life.