Whistler-mode auroral hiss emissions observed near Saturn's B ring

Abstract

An unusual whistler-mode emission, similar to terrestrial auroral hiss, was observed by the radio and plasma wave instrument on the Cassini spacecraft during the 1 July 2004 pass over the rings of Saturn. By using an electron density model that is consistent with measurements of the local electron plasma frequency, ray-tracing calculations have been performed to determine the source of the emission. The calculations assume that the emission is propagating near the whistler-mode resonance cone. It is found that the best fit to the V-shaped lower cutoff of the emission is obtained if the source is located very close to the B ring at a distance of about 1.76 R_S from the center of Saturn. On the basis of the close similarity to terrestrial auroral hiss we suggest that the emission is produced by a magnetic field-aligned beam of electrons that is directed outward away from the ring. The electron beam is most likely accelerated by parallel electric fields that arise as part of a current system induced by the interaction of the ring with the corotating magnetosphere of Saturn.