Martian core heat flux: Electrical resistivity and thermal conductivity of liquid Fe at martian core P-T conditions

摘要

The present-day Mars has no magnetic field which suggests that the heat carried out of its liquid core is largely driven by conduction. To constrain the heat flux from Martian core, we measured the temperature (T) dependent electrical resistivity of solid and liquid Fe devoid of contamination in large volume press at various fixed pressure (P) up to 22.5 GPa, corresponding to the P at the top of the Martian core. We also measured its P-dependent resistivity up to 22.5 GPa at room T. At a P range between 18 and 20 GPa, we observed a drop in the electrical resistivity of similar to 35 mu Omega cm which is attributed to a loss in long range order magnetic structure. This loss gives rise to an overall decrease in the electron scattering processes induced by magnon. The transition from long- to short-range order magnetic structure occurs in association with the completion of crystallographic transformation from alpha-bcc (ferromagnetic) to epsilon-hcp (paramagnetic). The decrease in the electrical resistivity at the same P range corresponds to an increase in thermal conductivity of similar to 30 Wm(-1) K-1. The resistivity and thermal conductivity of liquid Fe at the Martian core mantle boundary (CMB) on the cores side are estimated to be similar to 68 +/- 3 mu Omega cm and similar to 82 +/- 3 Wm(-1) K-1, respectively. The heat conducted along its core adiabat is found to be similar to 45 mW(-1) m(-2). With a core radius of similar to 1700 km, we obtain a value of 0.3 TW for its total surface heat flux. In comparison with the resistivity of Fe at the Earth's core conditions reported by a recent study, our result indicates that pure liquid Fe is electrically more conductive in the Martian core than in the Earth's core. Our results will complement the HP3 subsurface heat flux measurements in the on-going NASA InSight Mission.