Magnetic fields and charged particles around major planets and their satellites

Abstract

Jupiter and Saturn have magnetospheres whose large-scale structure can be understood by analogy with Earth, but the ways in which the magnetospheres differ are of great interest. At Earth, large-scale processes are dominated by convective plasma flows driven by the solar wind. At Jupiter, centrifugal effects driven by planetary rotation are critical. Magnetosphere particle sources include not only the ionosphere and the solar wind (as at Earth) but also satellites and rings. The internal planetary magnetic moments that control the scale of the magnetosphere differ by orders of magnitude between Jupiter and Earth. The magnetic moments have been modelled from spacecraft data but the restricted spatial sampling biases the results and limits confidence in details of the models. Because Jupiter is the only accessible protostar, it serves as a laboratory to test how well inferences from ground-based observations accord with in situ measurements. The agreement in some cases examined is reassuringly good but remote observations probe less than 0.1 % of the magnetospheric volume. Within that small volume, strong currents couple the moon lo with Jupiter s ionosphere. Voyager data give new insight into the lo story and suggest that lo may itself be magnetized and surrounded by an entirely unfamiliar type of magnetosphere.