Greifswald 2009 – scientific programme

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EP: Fachverband Extraterrestrische Physik

EP 14: Planets and Small Bodies III

EP 14.9: Talk

Thursday, April 2, 2009, 18:00–18:15, HS-Ost Pharmazie

Hydrogen and Helium at Megabar Pressures: Demixing and Metallization — •Bastian Holst, Winfried Lorenzen, Nadine Nettelmann, and Ronald Redmer — Institut für Physik, Universität Rostock, 18051 Rostock

Our current understanding of giant planets like Jupiter and Saturn is based on interior models that reproduce the observational constraints such as mass, radius, rotational period, and gravitational moments. Three-layer models that predict a central rock or ice core, a fluid layer of metallic hydrogen and helium, and an outer fluid envelope of molecular hydrogen and helium can be brought in accordance with these known characteristics by adjusting the location of the layer boundaries as well as the fraction of helium and heavier elements in each layer. A long-standing problem in this context is the behaviour of the fluid hydrogen-helium mixtures at high pressures. Phase separation and demixing into a helium-rich and a helium-poor phase would explain the lower helium content in Jupiter's outer region and the high luminosity of Saturn which exceeds the theoretical value based on homogeneous models by about 50%. We present new results of ab initio quantum molecular dynamics simulations based on finite-temperature density functional theory for fluid hydrogen-helium mixtures at megabar pressures. Our calculations predict that demixing of hydrogen and helium occurs in both planets.