Modeling of electron fluxes in the Enceladus plume

[1] Observations by instruments onboard the Cassini spacecraft of Saturn's icy satellite Enceladus have shown that a plume containing water vapor and ice grains is present in the southern hemisphere. Energy distributions of electrons in this plume were measured by the electron sensor part of the Cassini plasma spectrometer (CAPS – ELS). A significant suprathermal electron population was detected. The nature of the electron population is important for understanding the composition and chemistry of the plume plasma because the electron-ion recombination rate depends on the energy distribution and because ionizing collisions by energetic electrons creates new plasma. We present the results of a two-stream electron transport model for plume electrons that includes neutral densities that agree with Cassini Ion and Neutral Mass Spectrometer (INMS) data. Electron production within the plume due to photoionization by solar radiation and by electron impact ionization was included, as were energy losses due to electron-neutral collisions. Model cases were considered that both included and did not include electron inputs from outside the plume. Comparisons are made of model fluxes with measured fluxes by CAPS – ELS on October 9, 2008. The model-data comparisons indicate that photoelectrons (10 eV–70 eV energies) locally produced within the plume can explain the data. The possible role of electron-grain collisions was also explored and it was determined that nanograin densities in excess of 106 cm−3 would be needed to affect the electron distribution.