Thermal Conductivity of FeS and Its Implications for Mercury's Long-Sustaining Magnetic Field

The MESSENGER mission revealed that Mercury's magnetic field might have operated since 3.7-3.9 Ga. While the intrinsic magnetism suggests an active dynamo within Mercury's core, the mechanism that is responsible for sustaining the dynamo for prolonged period of time remains unknown. Here we investigated the electrical conductivity of Fe-S alloys at pressure of 8 GPa and temperatures up to 1,700 K. We show that the electrical conductivity of Fe-S alloys at 1,500 K is about 10(3) S/m, 2 orders of magnitude lower than the previously assumed value for dynamo calculations. The thermal conductivity was estimated using the Wiedemann-Franz law. The total thermal conductivity of FeS is estimated to be ~4 Wm/K at the Mercurian core-mantle boundary conditions. The low thermal conductivity suggests that a thermally driven dynamo operating on Mercury is more likely than expected. If coupled with chemical buoyancy sources, it is possible to sustain an intrinsic dynamo during time scales compatible with the MESSENGER observations.