Plasma wake of Tethys: Hybrid simulations versus Cassini MAG data

Abstract

The interaction between Saturn's fifth largest satellite, Tethys, and the corotating plasma of the inner magnetosphere has been studied with a three‐dimensional hybrid simulation. Since Tethys possesses neither an intrinsic magnetic field nor a substantial ionosphere, the moon's surface is directly exposed to the impinging plasma. This leads to the formation of an extended density cavity in the downstream region, expanding above and below Tethys along the magnetic field lines. The resulting deficit of plasma pressure is compensated by a compression of the field lines at the wakeside. By confronting our simulation results with Cassini magnetometer data from the so far only targeted flyby in 2005, we demonstrate that these key features of Tethys' plasma interaction are quantitatively reproducible within the framework of the hybrid model. Besides, the simulation results illustrate the importance of ambipolar electric fields for ion dynamics in the wake of Tethys.