Thermal Conductivity of Iron at the Conditions of Small Planetary Cores

Abstract

Planetary interiors cool and evolve over geologic time, and their thermal evolution depends on heat transport through their constituent layers. Here, the thermal conductivity of iron has been measured between 19 and 65 GPa and between 1700 and 2500 K in order to constrain its value at the conditions of small planetary cores. Our results are comparable to the low end of electrical resistivity experiments on fcc-Fe at comparable conditions, suggesting that the relationship between electrical and thermal conductivity described by the Wiedemann-Franz law provides a reasonable description of heat transport in fcc-Fe at planetary core conditions. The thermal conductivity of fcc-Fe at high pressures and temperatures places an upper bound on the thermal conductivity of Mercury's core, with a value of 52(7) W/m/K at 40 GPa, which corresponds to the pressure at the center of the core. Accounting for the effects of silicon and sulfur alloying reduces Mercury's core conductivity by 10%–40% for realistic core compositions, which satisfy constraints on Mercury's core density.