Experimental constraints on the chemical evolution of large icy satellites

We derive experimental constraints on the interior structure and mineralogy of large icy satellites by reacting material of chondritic chemistry with water at a pressure of 1.5 GPa, temperatures between 300°C and 800°C and a range of oxygen fugacities. Our results document the existence of three chemical processes that probably occur in large icy satellites as a result of high pressure hydrothermal processing: (1) the formation of low-density hydrated silicates, (2) the alloying of iron and sulfur to form FeS-dominated cores, and (3) the instability of organic material relative to carbonates. We construct new internal models of the thermal and structural state of Ganymede, and infer that the magnetic field of this body arises from convection within a mostly iron sulfide core. Simple thermochemical calculations are conducted to further explore the likely effects of composition and oxygen fugacity on the high pressure chemistry undergone by organic material within icy satellites. Both experimental and calculated results show that primordial organics are likely to have been largely oxidized to carbonates through hydrothermal processing early in Ganymede’s history, potentially sterilizing Ganymede’s H2O layer.