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

CaIrO₃-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 ∼10 megabars and ∼10,000 kelvin, cotunnite-type SiO₂ 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.