Observations of negatively-charged particle populations near Enceladus and its plume

We provide an overview of observations near Enceladus obtained by the Cassini Plasma Spectrometer's Electron Spectrometer, CAPS-ELS (Young et al. 2004). The instrument was designed to observe electrons between 0.6 eV/e and 28.8 keV/e in energy per charge, though, as we report here, other negatively-charged particles are also detectable by the instrument. A major hindrance to the comparison of particle data between Cassini’s Enceladus encounters has been the differing flyby geometries, speeds, and instrument pointing parameters. To help remove some of these complicating factors, we present the encounters grouped according to encounter geometry. We take stock of the CAPS-ELS data obtained near Enceladus, with reference to earlier studies by ourselves and others of nanograins, negative ions, and magnetic field-aligned electron beams. We also highlight features not yet published, some of which are only revealed when data from the 14 encounters are analysed collectively. These include electron dropouts and spikes in and near the plume, the effects on the spacecraft and plume material when in the optical shadow of Enceladus, and curious electron pulsations.