The molecular-metallic transition of hydrogen and the structure of Jupiter and Saturn

Recently, a new equation of state for hydrogen which predicts a molecular-metallic phase transition at finite temperature has become available. It is combined with a helium equation of state, and the resulting thermodynamic description of H/He mixtures is used to compute interior models of Jupiter and Saturn, subject to the constraints of the measured gravitational harmonics of both planets. We discuss the inferred heavy element abundance distribution in their interiors and the possible consequences on their formation. In particular, the Z-element enhancement and smaller core in Saturn relative to Jupiter, a conclusion of this study, may indicate a depletion of water ice in the Jupiter formation zone. In a companion paper, we investigate the effect of the molecular-metallic phase transition on the thermal evolution of Jupiter, Saturn, and brown dwarfs.