The plasma environment of Titan: The magnetodisk of Saturn near the encounters as derived from ion densities measured by the Cassini/CAPS plasma spectrometer

摘要

We analyze ion densities derived from the data of the Cassini Plasma Spectrometer for the time period of the prime mission till the end of May 2008, in the low latitude outer magnetosphere near Titan encounters. We have found that the central line of the magnetodisk is surrounded by a structured plasma sheet, a smooth, broad ion layer composed of light ions, and a heavy ion layer displaying narrow substructures. The heavy ion densities are spiky; the co‐location of the observed enhanced ion plasma densities with the change of sign of the radial component of the magnetic field is demonstrated. At these locations the heavy ion density is the highest. The plasma sheet is denser and wider on the dayside of Saturn than on the nightside; in the lobes the protons were dominant. Based on a statistical analysis for proton densities measured between radial distances from 10 R_S to 22 R_S we project densities to Titan’s orbital distance. We show that the projected proton density in the magnetodisk in organized by SLS3 longitude and, therefore, is modulated by SKR. In the lobes, the proton density is nearly constant. High heavy ion density in the sheet is accompanied by low heavy ion temperature. The magnetospheric interaction with Titan is primarily defined by the SLS3 phase of the encounter and the distance of the moon from the magnetic equator. Accordingly, the incoming plasma flow impinging on Titan cannot be stable for a few hours before the encounter.