Energetic aspects of Enceladus' magnetospheric interaction

摘要

We present an analytical model of the Poynting flux that is generated by the interaction between the plume of Enceladus and Saturn's magnetospheric plasma. Our purpose is to analyze the influence of two key elements of Enceladus' magnetospheric interaction on the electromagnetic energy radiated away in the moon's Alfvén wings. First, the north-south asymmetry of the obstacle generates a system of hemisphere coupling currents which allows a transport of electromagnetic energy into Saturn's northern hemisphere, even if the field-aligned currents connecting to the plume are completely blocked at the non-conducting icy crust of Enceladus. Second, the presence of electron-absorbing dust grains within the plume was recently found to drastically modify the electromagnetic field configuration within Enceladus' Alfvén wings (anti-Hall effect), thereby also altering the energy flux radiated away from the interaction region. By systematically studying the impact of varying strengths of the hemisphere coupling currents and varying electron absorption fractions on the energy flux, we come to the following conclusions: (1) The integrated Poynting flux into Saturn's southern hemisphere always exceeds the integrated flux into the northern hemisphere. In particular, the power transmitted towards the south may become several orders of magnitude larger than the power transmitted towards the north. (2) The search for Enceladus' auroral footprint has so far mainly focused on Saturn's northern hemisphere. However, based on the Poynting fluxes radiated away by the interaction, detections of the footprint should occur more likely in the giant planet's southern hemisphere, if no other far-field effects play a role. (3) Electron absorption by the dust grains within the plume makes a measurable contribution to the energy flux. Key Points Analytical model of the Poynting flux in Enceladus' Alfven wings Enceladus footprint should occur more frequently in the south than in the north Electron-absorbing dust makes measurable contribution to energy budget