Time-dependent MHD modeling of Titan's plasma interaction during T32, T85 and T96 and comparison to Cassini data

Abstract:

The Cassini Spacecraft flew past Titan on June 13, 2007 and found Titan was outside Saturn's magnetopause. During this pass (T32), observations showed dramatic changes of magnetic field orientation as well as plasma flow parameters during inbound and outbound segments. We have studied Titan’s ionospheric responses to such a sudden change in the upstream plasma conditions, using a sophisticated multi-species global MHD model. Simulation results of three different cases (steady state; simple current sheet crossing and magnetopause crossing) are presented and compared against Cassini Magnetometer (MAG), Langmuir Probe (LP) and Cassini Plasma Spectrometer (CAPS) observations. The simulation results provide clear evidence of the existence of fossil field. The MAG data can be well reproduced with a simple current sheet crossing. The Cassini plasma observations can only be reproduced by the magnetopause crossing case using plasma conditions constrained by CAPS observations. Real-time simulation also reveals how the fossil field formed during the interaction and shows the coexistence of two pile-up regions with opposite magnetic orientation, the formation of a pair of new Alfven wings and tail disconnection during magnetopause crossing process.

During two recent Titan flybys T85 and T96, Titan was found to be in the magnetosheath region of Saturn and in the solar wind, respectively. We present simulation results for those two flybys and compare features of Titan’s plasma interaction in different plasma environments.