Estimating the potential of ionizing radiation-induced radiolysis for microbial metabolism in terrestrial planets with rarefied atmospheres

Ionizing radiation is known to have a destructive impact on biology by causing damage to the DNA, cells, and production of Reactive Oxygen Species (ROS) among other things. While direct exposure to high radiation dose is indeed not favorable for biological activity, ionizing radiation can, and in some cases is known to produce a number of biologically useful products. One such mechanism is the production of biologically useful products via charged particle-induced radiolysis. Energetic charged particles interact with surfaces of planetary objects such as Mars, Europa and Enceladus without much shielding from their rarefied atmospheres. Depending on the energy of said particles, they can penetrate several meters deep below the surface and initiate a number of chemical reactions along the way. Some of the byproducts are impossible to produce with lower-energy radiation (such as sunlight), opening up new avenues for life to utilize them. For each of these cases, we calculate the energy deposition rate as a function of depth, and estimate the energy availability for potential metabolic activity. We discuss various mechanisms through which life could support itself utilizing the byproducts of these ionizing radiation-induced reactions, such as chemoautotrophs using solvated electrons, extracellular electron transfer, and indirect electrophy to facilitate processes like carbon fixation, nitrogen fixation and sulfate reduction, and possibly for ATP production.