Thermal Conductivity of Hydrogen at High Pressure and High Temperature: Implications to Giant Planets

Hydrogen (H2) is the most abundant constituent in giant planets, but its thermal conductivity ? under extreme pressure-temperature (P-T) conditions remains largely unknown. Here we report the ? of H2 from ambient to 60.2 GPa at 300 K and from 300 to 773 K at 2.1 GPa. At 300 K, the ? of liquid H2 fluctuates at & SIM;0.7-1.1 W m-1 K-1. Upon crystallization to H2-I phase, the ? jumps to 5.5 W m-1 K-1 at 7.2 GPa, and monotonically increases with pressure to & SIM;27 W m-1 K-1 at 60.2 GPa. Upon heating, the ? of liquid H2 at 2.1 GPa scales with T0.68. Moreover, the density (& rho;)-dependent compressional sound velocity (Vp) of liquid and solid H2 derived from Brillouin frequency data both follow the Birch's law. Besides the novel insights into the physics of thermal transport in H2 under extreme conditions, our results significantly advance the modeling of ?-Vp-& rho; relationship in a planet with H2. Hydrogen is the most abundant element in the universe and is also the major constituent in the giant plants (Jupiter, Saturn, Uranus and Neptune) in the solar system. Although most of the surface temperatures of those giant planets are colder than Earth's, their interior temperatures are actually able to reach several thousand degrees Kelvin. The heat flows within these giant planets are very active, while knowledge of heat conduction and propagation are largely unknown. This study investigates the high-pressure thermal conductivity of H2 at room temperature and high temperature conditions. Our results show that the liquid H2 exhibits low thermal conductivity, in the range of 0.7-1.1 W m-1 K-1 at high pressures and room temperature. However, appearance of solid H2 will increase thermal conductivity significantly and reach & SIM;27 W m-1 K-1 at 60.2 gigapascals and room temperature. Based on our model, the low thermal conductivity of liquid H2-He mixture may suppress the heat loss of the giant planets and explain why their surfaces are cold, but interiors are hot. Thermal conductivity of liquid H2 varies in the range of 0.7-1.1 W m-1 K-1 at high pressures and room temperatureThermal conductivity of solid H2-I increases from 5.5 W m-1 K-1 at 7.2 GPa to 27 W m-1 K-1 at 60.2 GPaOur model suggests that the thermal conductivity of liquid H2-He mixture is in the range of 0.70-1.0 W m-1 K-1 at 300K