MHD simulations of Io's interaction with the plasma torus

We compare results from magnetohydrodynamic computations of Io's interaction with the plasma torus with observations from the Galileo flyby. Both conducting and intrinsically magnetized models of Io are considered. Both models can reproduce many observed features of the interaction, including a high plasma density, a low plasma temperature, and a significant depression in magnetic field magnitude in Io's wake. The high plasma density in the wake is produced by ion pickup and concomitant slowing of the now and is not of ionospheric origin. The models also show important quantitative differences with the data. In particular, neither model reproduces large-scale structure on the flanks of the geometric wake. Neither model can be ruled out at the present time, but intrinsically magnetized models most easily match the magnitude of the maximum observed magnetic field depression in the wake. Comparison of results with future Galileo flybys past Io (planned for 1999) may help to clarify whether Io is magnetized.