Direct sound speed measurements of MgO along planetary adiabats up to 400 GPa using shock-ramp compression

Accurate models of planetary formation and evolution depend crucially on equation of state models for their constituent components. Currently, estimates of thermoelastic properties along Earth-like pressure and temperature states (the geotherm) rely on extrapolation of laboratory data in pressure and temperature which confounds clear interpretation of the physical and chemical state of Earth’s interior. Here we report the first-ever direct sound speed measurements of magnesium oxide, the most abundant non-silicate oxide in the Earth’s interior, along a geotherm-like adiabat up to 400 GPa using shock-ramp compression at the Z Machine at Sandia National Laboratories. Our experiments show excellent agreement with independent density functional theory and quantum Monte Carlo predictions, suggesting the technique can produce highly accurate thermoelastic data useful for interpreting the internal structure of terrestrial planets. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525