Energetic Particles from Planetary Magnetospheres

Abstract

It was not until the dawn of the space age that we discovered that the Earth’s magnetosphere was full of energetic particles. It was therefore reasonable to suppose that all planets with a strong magnetic field would have trapped energetic particles within their magnetosphere. All planets in the solar system which have a strong magnetic field have radiation belts and consequently are potential sources of energetic particles in the heliosphere. Bagenal (1992) has reviewed the features of the giant planet magnetospheres. Of the rocky inner planets only the Earth has a magnetosphere populated with trapped ions above 100 MeV/nuc and relativistic electrons. This is due to the fact that the Earth’s magnetic field is currently much more intense than that from Mercury, Venus and Mars. Mercury has a magnetosphere which contains energetic particles (Simpson et al. 1) but there is no evidence that they provide a significant contribution to the interplanetary population. It is clearly of interest to understand the acceleration mechanisms for the particles trapped in the planets’ magnetospheres; the loss mechanisms, which will have a bearing on the lifetime of the trapped particles; and what contribution they make to the radiation in the heliosphere. The solar wind pressure determines the sunward boundary of all the magnetospheres and some particle acceleration will take place at the bowshock.