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J. F. Cooper (Raytheon ITSS / GSFC), C. M. S. Cohen (Caltech), N. Gehrels (GSFC)
After general magnetospheric surveys by the earlier Pioneer and Voyager missions to Jupiter, the many Jovian satellite flybys of the Galileo Orbiter mission have provided unique opportunities to investigate the direct interactions of magnetospheric particles with the surfaces, atmospheres, and magnetic environments of the Galilean satellites. High energy (above 40 MeV) heavy ion data from the Heavy Ion Counter (HIC) have shown strong directional signatures of direct interactions with Io and Europa. Analysis and modeling of directional anisotropies from the satellite encounter data can be used to infer charge states of the ions, previously unknown at high energies, and to set limits on internal or induced magnetic fields. The initial J0 (Dec. 7, 1995) data downstream of Io with respect to plasma corotation could be consistent with an internal component reducing the total magnetic field in the satellite wake. However, the HIC data from the I24 (Oct. 11, 1999) and I27 (Feb. 22, 2000) encounters are conversely indicative of a strongly enhanced total field upstream of Io, more likely from external ionospheric interactions with the magnetospheric magnetic field and plasma. In the latter case the total field would be depressed in the satellite wake as seen during the J0 flyby. A similar magnetic configuration may be applicable to interpretation of HIC encounter data for Europa. The lead author is supported through Raytheon ITSS by NASA contract NAS5-98156 from the Space Science Data Operations Office (SSDOO) Project at Goddard Space Flight Center and by NASA research contract NASW-99029 from the Jovian System Data Analysis Program.
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