A Potential Energetic Driver for Phosphorylation on Europa

Europa is thought to contain processes that could produce oxidants and reductants necessary for biological activity. Redox cycling of Fe 2+ /Fe 3+ has been thought to be a redox pairing that biological activity could exploit for metabolic function. Phosphorus (P), another critical element for life, is usually in stable and poorly reactive orthophosphate minerals at equilibrium in geologic environments. In contrast to phosphate, the ion phosphite (HPO 3 2− ) is soluble and its oxidation couples to the formation of energetic polyphosphates. Here we investigate the far‐from‐equilibrium chemistry resulting from phosphite oxidation, as it may have occurred or may be occurring on Jupiter's moon Europa. Specifically, we consider potential sources of both phosphite and the oxidant hydrogen peroxide (H 2 O 2 ), which react to form polyphosphates. We further show the free energy of polyphosphates formed by this system to be on the order of 30 kJ/mol, with expectations of up to 55 kJ/mol of free energy available at micromolar P concentrations. The free energy in this system could have rivalled modern energy transfer molecules such as acetyl‐phosphate and ATP, especially as a precursor to these evolved molecules; therefore, Europa may have a potential prebiotic driver for metabolism in its subsurface ocean.