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L.E. Moore, M. Mendillo (Boston University)
Ion densities from the three-dimensional Saturn-Thermosphere-Ionosphere-Model (STIM, Moore et al. 2004) are extended above the plasma exobase using the formalisms of Lemaire (1976) and Pierrard and Lemaire (1996), which evaluate the balance of gravitational, centrifugal and electric forces on the plasma. The parameter space of low energy ionospheric contributions to Saturn’s plasmasphere is explored by comparing results that span the observed extremes of plasma temperature, 420o K to 1150o K, and the range of velocity distributions, Lorentzian to Maxwellian. In addition, plasmaspheric densities are generated for different seasons, solstice and equinox, and different solar fluxes, solar maximum and solar minimum. Finally, predictions are made for plasma densities along the path of the Cassini spacecraft’s orbital insertion on 1 July 2004. These predictions neglect any ring or satellite sources of plasma, which are most likely minor contributors at 1.3 Saturn radii. The absolute range of predicted electron density at closest approach is 10-4 – 101 cm-3, although increased knowledge of either plasma temperature or velocity distribution at Saturn’s plasma exobase would tighten this range considerably. For the most likely combination of plasma exobase parameters, the inner plasmasphere is predicted to be between 1-10 electrons cm-3 at Cassini's closest approach.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.