THE MAGNETIC-FIELD OF MERCURY

The magnetic field of Mercury was measured on two fly-bys of the plane t by the Mariner 10 space-craft. The presence of a field at Mercury is interesting for what it implies for both the internal and external so urces of field. The internal field of the planet is almost certainly g enerated by an internal dynamo although there remain many puzzles as t o how a dynamo is sustained given expectations of the thermal history of Mercury. The external sources of field are associated with the sola r wind interaction with the planet. There is a magnetospheric cavity f ormed about the planet in the solar wind. It seems likely that magneto spheric phenomena such as substorms and pulsations like those that occ ur 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 electrom agnetic processing of the outer layers of the planet by magnetospheric processes. (C) 1997 Elsevier Science Ltd.