Io's interaction with the plasma torus

A new model for the interaction of Io with the dense corotating plasma of the Io torus is described which involves pickup and Alfvén waves carrying a field‐aligned current. Pickup refers to the process whereby ions freshly created near Io are accelerated by the corotational electric field. It is shown that the pickup current is connected to a field‐aligned current carried by an Alfvén wave. The combination of currents allows for a self‐consistent determination of the electric field in Io's vicinity. Using a simplified solution for the electric field, we calculate the total pickup rate, field‐aligned current, enhancement of plasma density in Io's vicinity, thermal energy injected into the torus, UV radiation power, and inertial drag on the magnetosphere. All observations made by Voyager are compatible with an electron impact ionization mechanism and a neutral SO 2 Io atmosphere with a density of 10 9 cm −3 .