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J. F. Cooper (Raytheon ITSS, SSDOO Project, NASA Goddard Space Flight Center, Greenbelt, MD)
Data Analysis and modeling are in progress for Heavy Ion Counter (HIC) data from all Galileo Orbiter flybys of Io and Europa providing high resolution playback data to date. HIC count rate anisotropy data for oxygen and sulfur ions at total energies above 40 to 60 MeV show strong interactions of these large gyroradius ions with the satellite surfaces. Numerical models for the ion trajectories in the vicinity of these surfaces are sensitive to the local magnetic field structure including components from the Jovian magnetosphere, the satellite ionosphere, induced currents within subsurface oceans, and other internal sources. The best-fit model fields around Io are dominated by the magnetosphere - ionosphere interaction with no evidence for a fixed internal component. Initial results are discussed for modeling the Europa encounter data with respect to the magnetospheric interaction and induced fields from the putative ocean. Extension of this approach to lower energy ion data from the Energetic Particle Detector (EPD) could also be used to probe the neutral atmospheres. This work was supported at Raytheon ITSS through the Space Science Data Operations Office (SSDOO) and Jovian System Data Analysis Program (JSDAP) contracts funded by NASA's Office of Space Science.