Adiabatic heat flow in Mercury's core from electrical resistivity measurements of liquid Fe-8.5 wt%Si to 24 GPa

The effect of the core thermal conductivity on the heat flow along the adiabat is investigated using direct measurements of electrical resistivity of Fe 8.5Si at pressures from 5-24 GPa and temperatures above melting. Unexpected behaviour at low temperatures between 6-8 GPa may indicate an undocumented phase transition. Measurements of electrical resistivity at melting seem to remain constant at 127 mu.cm from 10-24 GPa, on both the solid and liquid side of the melting boundary. The adiabatic heat flow at the core side of Mercury's core-mantle boundary is estimated between 21.8-29.5 mWm(-2), considerably higher than most models of an Fe-S or Fe-Si core yet similar to models of an Fe core. Comparing these results with thermal evolution models suggests that Mercury's dynamo remained thermally driven up to 0.08-0.22 Gyr, at which point the core became sub-adiabatic and stimulated a change from dominant thermal convection to dominant chemical convection arising from the growth of an inner core. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study investigated the effect of the core thermal conductivity on heat flow along the adiabat using direct measurements of electrical resistivity of Fe 8.5Si. Unexpected behavior at low temperatures between 6-8 GPa may indicate an undocumented phase transition. The adiabatic heat flow at the core side of Mercury's core-mantle boundary is estimated to be considerably higher compared to most models of Fe-S or Fe-Si core, yet similar to models of an Fe core.