On Low Energy Electron Spikes Associated with Saturn's Moon Enceladus

Enceladus resides deep within Saturn's magnetosphere. The magnetospheric plasma incident on the satellite is absorbed, forming a thermal plasma wake downstream of the moon, and a cavity extending north-south in higher energy populations. When the Cassini spacecraft crosses Enceladus's L-shell, these cavities are observed as brief dropouts in energetic particle fluxes, termed microsignatures. A survey of thermal plasma observations by the Cassini Plasma Spectrometer's Electron Spectrometer (CAPS-ELS) instrument has revealed the existence of various features in low energy electrons close to and sometimes during the traversal of microsignatures. These features vary in characteristics; some present themselves as a set of discrete spikes, covering electron energies of ~9-15eV and lasting, intermittently, up to tens of minutes. Others, dispersed in time according to energy, show evidence of injection events. We present the results of a survey of these perplexing features, suggest possible causes for their occurrence including important clues from close Enceladus flybys.