Planetary Magnetospheres

Abstract

The study of planetary magnetospheres began almost a half century ago with the launch of Sputnik and Explorer 1, the first artificial satellites of the Earth. The exploration of other magnetospheres started not long after. Our understanding of our own space environment has grown ever deeper with the passing years as flotillas of spacecraft have gradually acquired measurements whose interpretation provides a good (although as yet imperfect) understanding of Earth’s environment in space. Our exploration of the magnetospheres of other planets has also progressed brilliantly but the high cost of planetary probes inevitably implies that we understand less about remote magnetospheres than about our own. Fortunately even limited data are of immense value in advancing the study of comparative magnetospheres because they reveal how magnetospheric processes respond to changes of scale, of rotation rate and of solar wind structure in the vicinity of the planet. This article addresses the topic of planetary magnetospheres by contrasting their properties with those familiar at Earth. The differences are related to key dimensionless parameters of the plasma flowing onto the different bodies of the solar system and to key properties of the central bodies such as the strength and symmetry of the magnetic field at the planet’s surface, the size and rotation period of the planet, the nature of its plasma sources and the conductivity of its surface layers.