Re-Analysis of Galileo Cassini & Voyager EUV Observations of the Io Plasma Torus

Abstract:

We present a survey of conditions observed in the Io plasma torus from the Voyager flyby, throughout the Galileo mission (1995 to 2003), & the Cassini flyby of Jupiter (fall 2000 to spring 2001). On the Cassini spacecraft the UVIS instrument made extensive observations of the spatial and temporal variations of torus emissions (Steffl et al. 2004, 2006). We re-analyze the Voyager, Galileo & Cassini EUV observations of torus emissions with a physical chemistry model based on Delamere et al. (2004) to derive modest spatial and temporal variations in torus model parameters (transport time, neutral source, population of hot electrons, ratio of neutral oxygen to sulfur atoms in the source). Torus plasma conditions (Temperature and mixing ratios of the different model species) derived from these emissions are also compared with in situ measurements by the Voyager PLS instruments and ground-based observations of torus emissions.