Dissociation of MgSiO3 in the cores of gas giants and terrestrial exoplanets

CalrO(3)-type MgSiO3 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 SiO2 at pressures and temperatures expected to occur in the cores of the gas giants and in terrestrial exoplanets. At similar to 10 megabars and similar to 10,000 kelvin, cotunnite-type SiO2 should have thermally activated electron carriers and thus electrical conductivity close to metallic values. Electrons wilt give a large contribution to thermal conductivity, and electronic damping will suppress radiative heat transport.