Dissociation of MgSiO 3 in the Cores of Gas Giants and Terrestrial Exoplanets

Abstract

CaIrO ₃ -type MgSiO ₃ is the planet-forming silicate stable at pressures and temperatures beyond those of Earth's core-mantle boundary. First-principles quasiharmonic free-energy computations show that this mineral should dissociate into CsCl-type MgO cotunnite-type SiO ₂ at pressures and temperatures expected to occur in the cores of the gas giants + and in terrestrial exoplanets. At ∼10 megabars and ∼10,000 kelvin, cotunnite-type SiO ₂ should have thermally activated electron carriers and thus electrical conductivity close to metallic values. Electrons will give a large contribution to thermal conductivity, and electronic damping will suppress radiative heat transport.