Dimitra Atri reports that photosynthesis is a mechanism developed by terrestrial life to utilize the energy from photons of solar origin for biological use. Subsurface regions are isolated from the photosphere, and consequently are incapable of utilizing this energy. This opens up the opportunity for life to evolve alternative mechanisms for harvesting available energy.
Bacterium Candidatus Desulforudis audaxviator, found 2.8 km deep in a South African gold mine, harvests energy from radiolysis, induced by particles emitted from radioactive U, Th and K present in surrounding rock. Another radiation source in the subsurface environments is secondary particles generated by galactic cosmic rays (GCRs). It has been concluded that it is a steady source of energy comparable to that produced by radioactive substances, and that the possibility of a slow metabolizing life flourishing on it cannot be ruled out. Two mechanisms are proposed through which GCR-induced secondary particles can be utilized for biological use in subsurface environments... i) GCRs injecting energy in the environment through particle-induced radiolysis and ii) organic synthesis from GCR secondaries interacting with the medium. Laboratory experiments to test these hypotheses are also proposed. Implications of these mechanisms on finding life in the Solar System and elsewhere in the Universe are discussed.
The GCR-induced radiolysis mechanisms proposed in the paper open up new possibilities of life in subsurface environments on a number of planetary bodies such as Mars, Moon, Europa, Enceladus, Pluto and especially ones with minor atmospheres. Radiolysis-powered life can either thrive independently, or can consume a combination of sources such as heat from chemical and geological processes. GCR-induced radiolysis can produce a number of ion species leading to the production of biologically useful products such as molecular hydrogen. There is a possibility of life on icy objects.
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