The magnetic field of Mercury

The magnetic field of Mercury was measured on two fly-bys of the planet by the Mariner 10 spacecraft. The presence of a field at Mercury is interesting for what it implies for both the internal and external sources of field. The internal field of the planet is almost certainly generated by an internal dynamo although there remain many puzzles as to how a dynamo is sustained given expectations of the thermal history of Mercury. The external sources of field are associated with the solar wind interaction with the planet. There is a magnetospheric cavity formed about the planet in the solar wind. It seems likely that magnetospheric phenomena such as substorms and pulsations like those that occur in the terrestrial environment occur in the Mercury magnetosphere. This fact not only tests our understanding of these processes at Earth but also carries strong implications that there is continual electromagnetic processing of the outer layers of the planet by magnetospheric processes.