Plasma waves in planetary magnetospheres

Abstract

With the completion of the Voyager 2 encounter with Neptune we have now surveyed the plasma wave spectra of five planetary magnetospheres: Earth, Jupiter, Saturn, Uranus, and Neptune. Here we provide a first general comparison of the various plasma wave modes at each of the planets with the use of a common format for displaying the spectra. The general conclusions are that many of the same types of wave modes are present in each of the magnetospheres, despite great differences in the magnetospheres' sizes, heliocentric distances, energy sources, plasma sources, and magnetic dipole orientations. There are, however, great differences in the relative and absolute intensity of some of the wave modes. Virtually ubiquitous in planetary magnetospheres are electron cyclotron harmonic bands and whistler mode emissions such as hiss and chorus. Ion cyclotron harmonic emissions have been observed where the observed local magnetic field strength was great enough to move these low‐frequency waves into the Voyager plasma wave receiver's frequency range. Broadband electrostatic noise has also been observed in the majority of the magnetospheres. In addition to a general survey of the magnetospheric wave modes, an initial assessment of the role of plasma waves in the precipitation of charged particles is presented. Waves seem to have obvious contributions in this aspect for Earth, Jupiter, and Uranus. Weaker wave amplitudes observed at Saturn and Neptune may possibly be due to the specific geometry of the flybys or to quiescent states of the magnetospheres during the encounters.