'Alfven wing' models of the induced electrical current system at Io - A probe of the ionosphere of Io

A novel class of models of the Alfven wing interaction between the Io plasma torus and Io's ionosphere has been developed and used to compute the magnetic field fluctuations at the position of the Voyager 1 flyby. These computations of the magnetic field signature are compared with the magnetic field measurements made during the flyby, and the differences between the model and observations are used as a probe of the structure of Io's ionosphere. The results of this model fitting indicate that a significant atmospheric neutral column density is required over a major part of the trailing hemisphere. This can be consistent with the cold-trap model for Io's neutral atmoshpere only if the major plumes near the center of the trailing hemisphere provide significant volumetric coverage. The Io plasma torus charged-mass density required for a proper match to the data is larger than earlier estimates based on the width of the Alfven wing signature.