Jupiter and Io: A binary magnetoshere

Abstract

The magnetosphere of Jupiter and Io has recently been traversed by two Voyager spacecraft. Since the earlier Pioneers were not equipped to measure spatially and spectrally resolved photon emissions from the Io torus and Jovian aurora, the dominant plasma components in the magnetosphere, or plasma waves and radio emissions, the Voyagers have provided qualitatively new information that is still not fully digested. This review outlines qualitatively the physical picture emerging from ongoing data analysis and theoretical interpretation. We discuss observations of the Io torus EUV emmissions and Jupiter's aurora, emphasizing the difficulty of accounting energetically for their luminosity. We next turn to Jupiter's middle magnetosphere, concentrating on the observations of corotating ions, their ambiguities, and their implications. We then return to the classical question of Jupiter's interaction with the solar wind, as manifested by its magnetic tail. Finally, guided by terrestrial magnetospheric experience, we attempt to construct a unifying conceptual picture which, though uncertain, falls within the latitude afforded by the current state of data reduction.