Magnetic Signatures of Charged Dust Grains in the Enceladus Plume

Abstract:

One of the most striking discoveries of the Cassini mission was the large plume of water vapor and dust, emanating from the south-polar regions of the small icy moon Enceladus. The interaction between this plume and Saturn’s magnetospheric plasma generates large-scale perturbations of the ambient magnetospheric field (called the Alfven wing) which have been detected by Cassini during all 20 targeted Enceladus flybys carried out so far. In recent years, it was found that absorption of magnetospheric electrons by negatively charged dust grains within the plume has a tremendous impact on the magnetic draping pattern: due to the lack of “free” magnetospheric electrons, the Hall current is carried almost exclusively by the positive ions, corresponding to a negative sign of the Hall conductance. This effect breaks the symmetry of the magnetic draping pattern between Enceladus’ Saturn-facing and Saturn-averted hemispheres and has been identified in all available magnetic field datasets from Cassini. In this presentation, we will review the physical mechanisms that lead to the “magnetic visibility” of the electron-absorbing dust population in the Enceladus plume. We will also discuss how magnetic field data can be applied to constrain e.g., the charging times of the dust grains and the pick-up of negatively charged nanograins from the plume.