Energetic electron spectra in Saturn's plasma sheet

Abstract

The differential spectra of energetic electrons (27-400 keV) in Saturn's plasma sheet can be characterized by power law or kappa distributions. Using all available fluxes from 2005 to 2010, fits to these distributions reveal a striking and consistent pattern of radial dependence in Saturn's plasma sheet (z < 1 RS = 60,268 km). The electron spectral indices show harder spectra at large radial distances (20-30 RS), softer spectra at middle radial distances (10-20 RS), and very steep spectra inside the orbit of Rhea (∼8.5 RS). The dayside spectra are somewhat harder than the nightside spectra outside the orbit of Titan (∼20 RS), although there is no local time dependence inside ∼10 RS. This spectral behavior exhibited essentially no dependence on pitch angle and remained remarkably constant throughout the Cassini mission. Inward of about 10 RS, the presence of the electron radiation belts and losses of lower-energy electrons to the gas and grain environment give rise to the very hard spectra in the inner magnetosphere, while the hard spectra in the outer magnetosphere may derive from auroral acceleration at high latitudes. The gradual softening of the spectra from 20 to 10 RS is explained by inward radial diffusion. Copyright 2011 by the American Geophysical Union.