Low-energy electrons in Saturn's inner magnetosphere and their role in interchange injections

Abstract

Since the days of Pioneer 11 and the Voyager missions, electrons have shown an unexplained peak in the data at approximately 7.5 Saturn radii (R_S). To investigate this peak, we examine near-equatorial electron energy flux data (±10°) from the Cassini Plasma Spectrometer Electron Spectrometer from 1 July 2004 through 10 August 2007. When these data are plotted versus L shell, a peak between L = 7.5 and L = 8 appears in the electron data in the 12-100 eV range. We show that this peak is associated with interchange injections. The electrons are separated into trapped (70°-110°) pitch angles and field-aligned (0°-20° and 160°-180°) pitch angles. The field-aligned electrons show stronger fluxes than the trapped electrons in the 12-100 eV range during these injections. In SLS3 coordinates, the trapped electrons peak at longitudes between 45° and 240° at 7-8 R_S with a smaller peak occurring between 310° and 360° SLS3 longitudes that penetrates to 6-5 R_S. The field-aligned electrons, however, show no SLS3 dependence.