Updating the Jovian Electron Plasma Environment

Reanalysis of the plasma science (PLS) experiments on the Voyagers (~10 eV to ~5 keV) and Galileo (~1 to ~50 keV) has refined our understanding of the electron environment responsible for spacecraft charging at and near the Jovian moon Europa. The low-energy 1-50-keV environment measured by the Galileo PLS has previously been at best poorly defined as the PLS electron data were found to have been contaminated by high-energy electrons. To address this issue, the raw PLS data have been reanalyzed orbit by orbit and detector by detector. The results indicate that the Voyager and the Galileo spectra, previously fit by the Maxwell-Boltzmann distributions, may be better fit by a more complex combination of Maxwell-Boltzmann plus kappa or a polynomial. The new spectra derived from the Voyager and Galileo PLS instruments are presented for a range of applicability from ~8 to ~40 Rj.