Time-varying magnetic fields of Mercury

In this study we derive spherical harmonic models of Mercury's magnetic field from measurements of the MESSENGER mission. The models describe large scale external and internal magnetic fields. The Gauss coefficients of the magnetic fields mainly show periodic temporal variations that are related to Mercury's orbital period around the sun. These periods are found for external and internal field variations, where internal field variations appear as internal variation, but may also originate in regions below MESSENGER and above Mercury's surface. It is known that magnetospheric fields are due to interactions of the planet's internal magnetic field and the interplanetary (solar) magnetic field. Previous research suggested internal field variations to be generated by an induction effect in Mercury's core. Such process may show a time lag between the causing external field variation and the core response. However, we do not find such time lag, which may be due to the limited temporal resolution of our analyzes. Furthermore, our new results suggest that magnetic fields may also be generated in Mercurys exosphere. Most likely by transient current systems. Possible mechanisms that generate these transient exospheric magnetic fields include wind-driven electrical current systems, and the diamagnetic effect. These results may hold implications for the production of electrically charged particles in Mercury's exosphere at altitudes upward 400 km above the Planet's surface, but also for the electrical conductivity of Mercury's mantle and crust.