Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsm23a0278d&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SM23A-0278
Physics
2154 Planetary Bow Shocks, 2756 Planetary Magnetospheres (5443, 5737, 6033), 2784 Solar Wind/Magnetosphere Interactions
Scientific paper
Ion composition measurements can provide an important clue to the origin of the suprathermal ions that are found in the foreshock region upstream from planetary obstacles such as the Earth's magnetosphere. This is particularly true at Saturn, where much of the magnetospheric plasma is made up of water group ions (O+, OH+, H2O+, H3O+), distinctly different from the solar wind composition of H+ and He++. Examination of the ion composition upstream from Saturn can thus reveal the extent to which magnetospheric leakage contributes to the foreshock ion populations, as opposed to shock-related processes that accelerate them out of the incident solar wind plasma. Surveying nineteen months of Cassini Plasma Spectrometer (CAPS) data, we obtained 45 hours of mass-resolved observations using the CAPS Ion Mass Spectrometer (IMS) to sample the suparathermal plasma in Saturn's foreshock region. In the energy range between 3 and 50 keV/q, the foreshock ions are found to be dominated by H+ and m/q=2, presumably He++. After subtracting the background, the ratio of suprathermal water group ions to hydrogen ions is less than one percent (and consistent with zero), implying that in this energy range, magnetospheric leakage is not the source of foreshock ions. The more energetic O+ ions in the foreshock reported by Krimigis et al. [2005] thus appear to be due to direct leakage of already energized magnetospheric particles, as opposed to upstream acceleration by bow shock related processes. A further study of the composition of Saturn's magnetosheath, the region between the foreshock and magnetosphere, may shed additional light on the origins of suprathermal ions in the foreshock.
Andre Nicolas
Crary Frank J.
Delapp D. D.
Dilorenzo J.
McComas David John
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