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E C Sittler (NASA/Goddard Space Flight Center), N Andre, M Blanc (CESR), A Coates (Mullard Space Science Laboratory), R E Johnson, R A Baragiola (University of Virginia), R E Hartle (NASA/Goddard Space Flight Center), D Reisenfeld (University of Montana), M Thomsen (Los Alamos National Laboratory), D Chornay (University of Maryland College Park), M Shappirio, D Simpson (NASA/Goddard Space Flight Center), M Dougherty (Imperial College London), F Crary, D J McComas, D T Young (Southwest Research Institute)
We will present fluid parameters derived from Cassini Plasma Spectrometer (CAPS) observations of ions and electrons within Saturn’s inner magnetosphere as presented in Sittler et al. [2005]. From these parameters one can estimate the ion total flux tube content per L shell, NL^2, for protons and water group ions as a function of radial distance or L shell. When we do this, the calculation shows that the dominant ion production is confined within the L shells of Dione and Rhea and not within the vicinity of Enceladus’ L shell, L ~ 4, where most of the neutral oxygen and OH have been observed by Cassini (Esposito et al., 2005) and HST (Shemansky et al., 1993; Richardson et al., 1998), respectively. Within the inner most regions of the magnetosphere, the plasma is very cold and ionization rates due to electron impact are small so that photoionization may be the only important mechanism for ion production in the vicinity of Enceladus’ L shell. We would argue that the primary sink for the neutral clouds at L ~ 4 is charge exchange, which just replaces one ion with another, and therefore does not contribute to ion production. However, it can contribute to compositional changes in the plasma with radial distance and/or redistribution of the plasma in energy space. We will discuss these issues and how they relate to the sources of neutrals within Saturn’s inner magnetosphere.
1. Sittler et al., GRL, 32, L14S07, 2005. 2. Esposito et al., Science, 307, 1251, 2005. 3. Shemansky et al., Nature, 363, 329, 1993. 4. Richardson et al., J. Geophys. Res., 103, 20245, 1998.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.