Alternative Energy: Production of H-2 by Radiolysis of Water in the Rocky Cores of Icy Bodies

摘要

We applied a model of radiolysis in earthly rock-water mixtures to several known or suspected ocean worlds: Enceladus, Ceres, Europa, Titania, Oberon, Pluto, and Charon. In this model, radiation emitted by the long-lived radionuclides (K-40, Th-232, U-235, and U-238) contained in the ordinary chondrite-like rocks is partly absorbed by the water permeating the material of each body's core. The physical and chemical processes that follow release molecular hydrogen (H-2), which is a molecule of astrobiological interest. We compared the calculated production of H-2 by radiolysis in each body's core to published estimates of production by serpentinization. This study presents production calculations over 4.5 Gyr for several values of rock porosity. We found that radiolysis can produce H-2 quantities equivalent to a few percent of what is estimated from serpentinization. Higher porosity, which is unlikely at the scale of a body's entire core but possible just under the seafloor, can increase radiolytic production by almost an order of magnitude. The products of water radiolysis also include several oxidants, allowing for production of life-sustaining sulfates. Though previously unrecognized in this capacity, radiolysis in an ocean world's outer core could be a fundamental agent in generating the chemical energy that could support life.