Large scale changes in the highly energetic charged particles in the region of the Io torus

Abstract

The Galileo star sensor is heavily shielded from penetrating radiation to prevent false counts. Nevertheless in the inner jovian magnetosphere the penetrating radiation appears to be sufficiently strong that significant background counting rates are seen. The morphology and time variation of these background rates are consistent with the hypothesis that they are caused by energetic trapped particles. On the C22 pass through the torus region the count rates were unusually high as if a particularly large disturbance had occurred. We speculate that such disturbances arise at times of rare but intense volcanic activity at Io that causes intense temporal fluctuations in the magnetic field and enhanced radial diffusion and particle energization.