This study reports direct detection by the Cassini plasma spectrometer of freshly‐produced water‐group ions (O+, OH+, H2O+, H3O+) and heavier water dimer ions (HxO2)+ very close to Enceladus where the plasma begins to emerge from the plume. The data were obtained during two close (52 and 25 km) flybys of Enceladus in 2008 and are similar to ion data in cometary comas. The ions are observed in detectors looking in the Cassini ram direction exhibiting energies consistent with the Cassini speed, indicative of a nearly stagnant plasma flow in the plume. North of Enceladus the plasma slowing commences about 4 to 6 Enceladus radii away, while south of Enceladus signatures of the plasma interaction with the plume are detected 22 Enceladus radii away.

[1] Periodic plasma enhancements are examined for all Cassini orbits from December 29, 2005 through September 7, 2006. The events, which have UT durations of 3 -4 hours, are centered near SLS3 longitude 10°at radial distances near 15 R S and at larger W longitudes at larger distances, reaching 180°W by 49 R S . Magnetic-field data within the events and outside 30 to 35 R S show signatures of neutral-sheet crossings and magnetic reconnection (i.e., plasmoids). We conclude that plasmoids move outward from 30 -35 R S along a spiral path that rotates with the planet. The duration of these events is similar to that of SKR events, and they are ordered in the SKR-based SLS3 longitude system. A conceptual model, in which the plasmoids are triggered in the pre-midnight quadrant following (with a predictable delay) the appearance of SKR at the magnetopause and then propagate outward in a rotating spiral pattern, can explain the connection among periodicities observed in Saturn's charged particles, magnetic fields, and kilometric radiation. Citation: Burch,

The jovian system is of particular interest for studying magnetic induction in icy ocean worlds. Jupiter has a strong magnetic field whose dipole axis is tilted 9.6° with respect to its rotation axis (Acuna & Ness, 1976), while the orbits of the Galilean moons lie very nearly in the equatorial plane of Jupiter. This means that Jupiter's magnetic field varies in time at the orbital positions of the satellites. Also, the outer layers of the

Ion cyclotron motion can play a role in shaping magnetospheres and governing magnetospheric dynamics, particularly in weakly magnetized systems such as the moons of outer planets. However, MHD explicitly neglects such effects. We demonstrate the importance of ion cyclotron motion in the near space environment of Ganymede using 3‐dimensional multi‐fluid simulations to account for Galileo magnetometer data from several flybys through various regions of Ganymede's magnetosphere. These simulations track several ion species and incorporate ion cyclotron effects through a comprehensive treatment of the plasma dynamics and the generalized Ohm's law equation. In the ideal MHD limit of the multi‐fluid formulation the size of Ganymede's magnetosphere is underestimated, while in the full multi‐fluid treatment the magnetosphere is shown to be in good agreement with magnetometer measurements from Galileo. The importance of treating the ion cyclotron motion is most noticeable near the magnetopause where magnetic field strengths approach zero.