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 R j. 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 x l0 s per R r The electron density profile, inferred from the ion density measurements, has two maxima at 5.7 and 5.3 R r A twodimensional 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 R r