Importance of Heavy Elements in Giant Planet Interiors.

Abstract:

Numerous extrasolar giant planets have been discovered. Yet many questions remain unanswered regarding their structure, formation and evolution. Their relatively low mean density indicates that they must be primarily composed of hydrogen and helium, probably in a cosmological proportion. The mass-radius measurements also showed that these planets must contain some heavier elements, which is expected assuming they were formed by core accretion. From the observations it is unclear however how the different materials are distributed in the interiors of these planets.

While ab initio simulations and shock experiments have helped to constrain the properties of hydrogen-helium mixtures at high pressures, little is known about the role of heavy elements, Z, in these mixtures. To model the interiors of giant planets, it is important to understand how ternary hydrogen-helium-Z mixtures behave at high pressure and to what extend their properties can be described with an ideal mixing approximation that is based on additive volume rule Here we present our results of ab initio simulations and describe the influence of heavy elements on the thermodynamic, and chemical properties of H-He-Z mixtures. We compare different mixing approximations and conclude by discussing the consequences for the modeling of giant planets.