Mass loading of Saturn's magnetosphere near Enceladus

摘要

The Cassini spacecraft has made three close flybys of Enceladus. The magnetic field from the first flyby clearly showed that Enceladus acts as an obstacle to the magnetized flow resulting in field line draping. The second flyby confirmed the draping pattern but hinted that the effective source must be located below Enceladus and demonstrated that Enceladus does not possess a measurable internal magnetic field. In situ and remote sensing observations on the third flyby provided conclusive evidence of a large vent outgassing near the south pole of Enceladus and confirmed the southern offset of the center of draping. In this work, we model the magnetic field data collected from the three flybys in order to quantify the strength of the Enceladus/plasma interaction. We show that the effective diameter of the obstacle is at least 6 R E, and the obstacle is displaced by >2 R E south of Enceladus and downstream by at least ～1 R E. The total current produced in the interaction is <105 Amps (40–60% of the Neubauer limit). We estimate that the mass picked up by the plasma within 5 R E of Enceladus is <3 kg/s. Additional pick up must be occurring in the neutral torus extending outward from the orbital location of Enceladus.