Energetic ion characteristics and neutral gas interactions in Jupiter's magnetosphere : Cassini flyby of Jupiter

[1] Spectra, integral moments, and composition (H, He, O, S) of energetic ions (50 keV to 50 MeV) are presented for selected Jupiter magnetospheric positions near the equator between radial distances of ∼6 to ∼46 Jupiter radii (R J ), as revealed by analysis of the Galileo Energetic Particle Detector data. These characteristics are then used as the basis of interpreting and modeling reported signatures of energetic ion/neutral gas interactions within Jupiter's inner magnetosphere, particularly energetic neutral atom emissions measured during the Cassini spacecraft flyby of Jupiter. Key findings include the following: (1) sulfur ions significantly dominate the energetic (>50 keV) ion density and pressure at all radial distances >7 R J ; (2) protons dominate integral number and energy intensity planetward of 20-25 Rj; (3) a distinct signature of local, equatorial acceleration of energetic protons is revealed between Io (5.9 R J ) and Europa (9.4 R J ); (4) significant spectral and compositional signatures of neutral gas interactions are also revealed between the orbits of lo and Europa; (5) a previously reported significant depletion of ring current ion populations between Io and Europa during the early-phase operation of Galileo (∼1995), as compared with observations obtained during the Voyager epoch (1979), has persisted and probably deepened during later Galileo phases (1999); and (6) detailed energetic neutral atom emission modeling, based on the in situ results reported here, further constrains recent estimates of the contents of the neutral gas torus of Europa.