Hydrogen at high pressures and temperatures: Implications for Jupiter

Abstract

Electrical conductivities and shock temperatures were measured for shock-compressed liquid H 2 and D 2 . Conductivities were measured at pressures of 93-180 GPa (0.93-1.8 Mbar). Calculated densities and temperatures were in the range 0.28-0.36 mol/cm 3 and 2000-4000 K. The resistivity data are interpreted in terms of a continuous transition from a semiconducting to metallic, primarily diatomic fluid at 140 GPa and 3000 K. Shock temperatures up to 5200 K were measured at pressures up to 83 GPa. These data are interpreted in terms of a continuous dissociative phase transition above 20 GPa. The continuous transition from a molecular to monatomic fluid means that Jupiter has no distinct core-mantle boundary. The dissociation model derived from the temperature measurements indicates a dissociation fraction of about 5% at 140 GPa and 3000 K. The isentrope of hydrogen was calculated starting from the surface temperature of Jupiter (165 K). At a metallization pressure of 140 GPa in Jupiter, the temperature is about 4000 K and about 10% of the hydrogen molecules are dissociated. The electrical conductivity was calculated along this isentrope by deriving a scaling relationship from the measured conductivities. The results indicate that hydrogen becomes metallic much closer to the surface of Jupiter than thought previously, a possible explanation of the very large magnetic field of Jupiter, but the metallic conductivity of the molecular fluid is two orders of magnitude lower than predicted for the monatomic fluid.