Comparisons between MHD model calculations and observations of Cassini flybys of Titan

Abstract

The Cassini spacecraft passed by Titan on 26 October 2004 (Ta flyby) and 13 December 2004 (Tb flyby). In both cases the Cassini Orbiter entered Titan's ionosphere and flew through Titan's dynamic wake region. In this paper, we present our simulation results of these two flybys using our three-dimensional multispecies MHD model. This model is a slightly updated version of the model outlined by Ma et al. (2004a); the main difference is the inclusion of magnetic diffusion into the equations. The calculations used the best available upstream plasma and magnetic field parameters obtained by the Cassini instrument complement. The calculated parameters, corresponding to the Cassini flybys near the closest approach, are compared with the relevant observed values. There is a reasonably good but clearly not perfect agreement between the measured and calculated values. Some of these differences are believed to be due to the uncertainties and time variability associated with the upstream parameters and some differences must definitely be the result of the uncertainties in the parameters selected for the model, as well as the limitations associated with the MHD approximations.