Assessment of the magnetospheric contribution to the suprathermal ions in Saturn's foreshock region

[1] Nineteen months of Cassini Plasma Spectrometer measurements are surveyed for episodes of suprathermal ions upstream from Saturn's bow shock. A total of 45 hours of mass-resolved observations are obtained. Suprathermal ions (between 3 and 50 keV/q) in Saturn's foreshock are found to be dominantly comprised of H+ and ions with m/q = 2, presumably solar wind He++, with no detectable contribution from magnetospheric water group ions. In light of the dominant contribution of water group ions to the hot plasma of the outer magnetosphere, it thus appears that magnetospheric leakage is not a significant source of upstream ions in this energy range. One implication is that the more energetic O+ ions reported recently most likely originate from direct leakage of already-energized magnetospheric particles, rather than from their upstream acceleration by bow shock-related processes.