Ion Composition in Jupiter's Inner and Middle Magnetosphere

Details Ion Composition in Jupiter's Inner and Middle Magnetosphere Ion Composition in Jupiter's Inner and Middle Magnetosphere

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsm12c..05w&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SM12C-05

Other

2756 Planetary Magnetospheres (5443, 5737, 6030), 5737 Magnetospheres (2756), 6218 Jovian Satellites

Scientific paper

While sputtering from Jupiter's moons is considered to be the ultimate origin of the non-thermal heavy ion population observed by in situ spacecraft, the nature of its evolution remains an open question in magnetospheric physics. Galileo's comprehensive observations of energetic ions in the Jovian magnetosphere between 9 and 30 R {J} are used to investigate the relative contribution of various source populations as well as the subsequent acceleration and transport that the plasma experiences. Energetic Particles Detector (EPD) measurements of protons, oxygen and sulfur ions over consecutive energy pass-bands between .01-1 MeV/nucl display a strong radial dependence between 12 and 20 R {J}, with ion intensities decreasing several orders of magnitude over increasing radial distance from Jupiter. Ion energy spectra soften considerably in this transition region as well, from a power law spectral index of γ ˜ 1-2 in the inner magnetosphere to a near-constant value of γ ˜ 3 in the plasma sheet. In general, the heavy ion species are more concentrated in the inner magnetosphere and display softer spectra than the energetic protons, suggesting different transport mechanisms and plasma sources for the two populations. Simultaneous measurements of ˜100 MeV oxygen ions made by the Galileo Heavy Ion Counter (HIC) reveal that differential oxygen intensity is well ordered by particle energy normalized to the local magnetic field strength, E/B. Extrapolation of the EPD particle intensity using the measured spectral index is performed to yield species abundance ratios at E=25 keV/nucl throughout the inner and middle Jovian magnetosphere. The S/O abundance ratio exhibits little variation with radial distance, and its near constant value of 0.5 is consistent with an Iogenic SO2 dissociation source. These results are presented in the context of other reported abundance ratios measured at different energy/nucleon ranges, and the implications for the inferred ion charge states are discussed.

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