Spatial distribution of plasma in the Io torus

In situ measurements of ion densities and temperatures have been analyzed to produce profiles of these plasma parameters along the Voyager 1 inbound trajectory between 7 and 5 RJ. The temperature profile shows a sharp decrease by a factor of ∼50 between 5.8 and 5.2RJ corresponding to a temperature gradient of ∼7 × 105 per RJ. The electron density profile, inferred from the ion density measurements, has two maxima at 5.7 and 5.3 RJ. A two‐dimensional model of the spatial distribution of various ionic species in the Io plasma torus has been constructed. Using this model a contour map of electron density in a meridional plane has been made, it exhibits a well‐defined inner edge to the torus at 5.6 RJ. The contour map of S+ ion density indicates that most of the S+ ions are concentrated close to the centrifugal symmetry surface and radially inward of the larger electron density maximum near 5.7 RJ.