Properties of hydrogen, helium, and silicon dioxide mixtures in giant planet interiors

Recent observations of Jupiter and Saturn provided by spacecraft missions, such as Juno and Cassini, compel us to revise and improve our models of giant planet interiors. Even though hydrogen and helium are by far the dominant species in these planets, heavy elements can play a significant role in the structure and evolution of the planet. For instance, giant-planet cores may be eroded by their surrounding fluid, which would result in a significantly increased concentration of heavy elements in the hydrogen-helium envelope. Furthermore, the heavy elements could inhibit convection by creating a stabilizing gradient of composition. In order to explore the effects of core erosion, we performed ab initio simulations to study structural, diffusion and viscosity properties of dense multi-component mixtures of hydrogen, helium, and silicon dioxide at relevant pressure-temperature conditions. We computed radial distribution functions to identify changes in the chemical behavior of the mixture and to reveal dissociation trends with pressure and temperature. The computed diffusion coefficients of the different species as well as the viscosity provide constraints for the time scale of the dynamics of the core erosion and the mixing of its constituents into the envelope, which will help improve planetary models.