A new model of Mercury's magnetosphere

There have been several attempts to model the magnetosphere of Mercury based on simply scaling models of the Earth's magnetosphere. While this approach has had many successes, it remains physically unsatisfactory, as it ignores the fundamentally different boundary conditions that apply at the two planets. The higher solar wind dynamic pressure and smaller dipole moment at Mercury make its magnetosphere very small and highly dynamic; solar wind driven convection is the dominant plasma transport process. The stronger interplanetary magnetic field means that reconnection may proceed more efficiently, making the magnetosphere adopt a very open configuration. There are no trapped particles, and therefore no ring current can form at Mercury. In addition, field aligned currents may be insignificant due to the lack of an ionosphere. In this work, we analyse existing magnetospheric modelling techniques, particularly those of Tsyganenko, and attempt to apply them directly to Mercury with these different boundary conditions in mind. The lack of data has made the parameterisation of the model very difficult. However, we present fits to Mariner 10 data demonstrating the flexibility of the model. As new data becomes available from Messenger and BepiColombo it will be easily incorporated into the model.