The Galileo Heavy Ion Environment as Modeled by the HIC Experiment

The Galileo Heavy Ion Counter (HIC) monitored the high energy (~6 to >200 MeV/nuc), heavy ion (6C--28Ni) fluxes at Jupiter and returned data for all but 2 of the 35 orbits of the Jupiter system from 1995 to 2003. The HIC experiment, based on a re-engineered Voyager Cosmic Ray System instrument, was added to gain a better understanding of the heavy ion radiation environment at Jupiter than that given by the Pioneer and Voyager flybys. HIC, as did these spacecraft, found Oxygen and Sulfur to be the primary constituents in the heavy ion environment at Jupiter. In addition, Carbon was also observed. Whereas the Carbon is believed to be of solar origin, the Oxygen is assumed to be of mixed solar origin and sputtering off the icy moons of Jupiter while the Sulfur is believed to be primarily Io-genic. In earlier presentations, a “HIC Model” was generated from the instrument data to provide estimates of the SEU environment for Jupiter. This presentation, based on an update to the HIC real time event data, provides estimates of the Carbon, Oxygen, and Sulfur fluxes, F, in terms of a power law fit of the form: F(E,Rj) = Fo (E-a) (1+E/Eo)-b where E is the energy and Rj is the radial distance from Jupiter. The spectra were determined at discrete radial distances between 5 and 25 Rj. The resulting fits provide simple but useful estimates of these important background particle species.