Planetary magnetospheres

Abstract

The Pioneer, Mariner and Voyager spacecraft have presented us with a bewildering variety of planetary magnetospheres. The Earth's magnetosphere, because of its proximity, is the best understood. The solar wind supplies some plasma and, most important, the power to drive the wide range of phenomena observed in the Earth's magnetosphere. For Earth, the ionosphere is the primary source of magnetospheric plasma. In contrast, the plasma in Jupiter's magnetosphere is largely derived from volcanic gases that escape from its satellite Io (and secondarily from the Jovian ionosphere), and the power for Jupiter's magnetosphere is supplied by the kinetic energy of Jupiter's spin. Thus, the solar wind is not an important source of plasma or energy for Jupiter. Jupiter's magnetosphere demonstrates complex patterns of behavior. For example, Jovian magnetospheric phenomena are, in general, not axially symmetric. Nearly all are organized so that they occur within a single -160° range of longitude known as "the active sector". Differences and similarities in what has turned out to be a virtual zoo of magnetospheres test our basic understanding of magnetospheric processes and lead us to develop new, more general principles of magnetospheric physics. Jupiter's magnetosphere, being the most dynamic and having the least in common with other solar system magnetospheres, is perhaps the most interesting of the variety now available for comparative study.