The Variable Enceladus-Saturn Interaction

Probably the most remarkable discovery of the Cassini mission to date is that of substantial outgassing of neutral gas and dust from fissures on the southern pole of Enceladus, dubbed the Enceladus 'plumes'. Ionisation in the plumes provides local plasma loading near Enceladus. Since it is well known that Io and Europa produce strong UV emission at their footprints in Jupiter's ionosphere members of the Cassini science teams were motivated to search for an analogous auroral footprint associated with plasma loading at Enceladus. During an Enceladus encounter in 2008 the Cassini spacecraft observed anti-planetward energetic field aligned ions and low energy field aligned electrons. Anti-planetward ions and electrons have been associated with the downward auroral current region. Two weeks later the Cassini observed a faint glowing UV spot in Saturn's northern ionosphere, confirming the electromagnetic link between Enceladus and Saturn. These and other observations strongly suggest that the coupling of Encleadus and Saturn is variable - suggestively due to variable ice volcanic activity on Enceladus. It is important, however, to note that both variability of the auroral footprint emission and plasma enhancements near Enceladus are coupled with Saturn's variable plasma environment - and so the association is by no means trivial. We will describe the connection of Enceladus with Saturn based on the most recent Cassini-era observations and outline the case for the various sources of variability in the Enceladus-Saturn connection.