We study the thermophysical properties of warm dense hydrogen using quantum molecular dynamics simulations. New results are presented for the pair distribution functions, the equation of state, the Hugoniot curve, and the reflectivity. We compare with available experimental data and predictions of the chemical picture. Especially, we discuss the nonmetal-to-metal transition which occurs at about 40 GPa in the dense fluid.

The amount and distribution of heavy elements in Jupiter gives indications on the process of its formation and evolution. Core mass and metallicity predictions however depend on the equations of state used, and on model assumptions. We present an improved ab initio hydrogen equation of state, H-REOS.2 and compute the internal structure and thermal evolution of Jupiter within the standard three-layer approach. The advance over our previous Jupiter models with H-REOS.1 by Nettelmann et al. (2008) is that the new models are also consistent with the observed 2 times solar heavy element abundances in Jupiter's atmosphere. Such models have a rock core mass M c = 0-8 M ⊕ , total mass of heavy elements M Z = 28-32 M ⊕ , a deep internal layer boundary at ≥ 4 Mbar, and a cooling time of 4.4-5.0 Gyrs when assuming homogeneous evolution. We also calculate two-layer models in the manner of Militzer et al. (2008) and find a comparable large core of 16-21 M ⊕ , out of which ∼ 11 M ⊕ is helium, but a significantly higher envelope metallicity of 4.5× solar. According to our preferred three-layer models, neither the characteristic frequency (ν 0 ∼ 156 µHz) nor the normalized moment of inertia (λ∼ 0.276) are sensitive to the core mass but accurate measurements could well help to rule out some classes of models. Subject headings: planets and satellites: individual(Jupiter) -equation of state

The equation of state of hydrogen, helium, and water effects interior structure models of giant planets significantly. We present a new equation of state data table, LM-REOS, generated by large scale quantum molecular dynamics simulations for hydrogen, helium, and water in the warm dense matter regime, i.e. for megabar pressures and temperatures of several thousand Kelvin, and by advanced chemical methods in the complementary regions. The influence of LM-REOS on the structure of Jupiter is investigated and compared with state-of-the-art results within a standard three-layer model consistent with astrophysical observations of Jupiter. Our new Jupiter models predict an important impact of mixing effects of helium in hydrogen with respect to an altered compressibility and immiscibility. Subject headings: planets and satellites: individual (Jupiter) -equation of state

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We present results of ab initio finite-temperature density functional theory molecular dynamics simulations for fluid hydrogen-helium mixtures at megabar pressures. The location of the miscibility gap is derived from the equation of state data. We find a close relation between hydrogen-helium phase separation and the continuous nonmetal-to-metal transition in hydrogen. Our calculations predict that demixing of hydrogen and helium occurs in Saturn and probably also in Jupiter. These results will have a strong impact on interior models of giant solar and extrasolar planets.