Io's wobbling flux tube and nonuniform surface conductivity: Longitude control of decametric emission and other magnetospheric interactions

Abstract

A model is proposed relating Io's modulation of Jupiter's decametric radio emission (DAM) and other magnetospheric interactions to periodic changes in flux tube orientation with Io’s surface of nonuniform surface electrical conductivity. Spectral reflectance and albedo data suggest that visually bright surface areas on Io may be highly conducting due to the abundance there of irradiation‐altered salts, while relatively dark areas may be extremely insulating due to the abundance of free sulfur. Geometric correlations show that Io's orbital motion through Jupiter's tilted and offset magnetic field results in a 13‐hour periodic variation in the Io‐graphic surface position of Io's flux tube contact junctions. The resulting variation in effective electrical conductivity of Io results in modulation (switching) of Io's motional emf currents and corresponding flux tube currents. This causes the observed magnetic‐longitude dependence of Io‐dependent DAM, while emission beaming accounts for the observed Io‐phase effect. This switching model suggests that Io is a variable unipolar inductor and that its flux tube varies in electrodynamic character as a function of magnetic longitude; the predicted behavior is consistent with pre‐Voyager observed particle‐injection spikes at Io's L shell, auroral emissions from Jupiter, and may reconcile inconsistencies between theoretical and observed particle sweeping effects of Io. The model predicts a relatively inactive flux tube current system and strong particle sweeping during the Voyager 1 flux tube crossing.