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L. Moore, M. Mendillo (Boston University), I. Mueller-Wodarg (Boston University and Imperial College)
The Saturn-Thermosphere-Ionosphere-Model (STIM) -- a global circulation model -- is used to study parameters in Saturn's ionosphere that affect the location and magnitude of the electron density peak. Past observations from the Pioneer and Voyager spacecraft indicated that the ionosphere had a peak between ~1900 - 2900 km, with a maximum density ranging from 6000 - 20,000 electrons/cc. Preliminary results from the first occultation by Cassini show an ionospheric peak of somewhat fewer than 10,000 electrons/cc near 1200 km, and a peak of order 1000 electrons/cc near 2500 km. We use STIM to explore parameter space for processes that could lead to the dawn/dusk asymmetries present in the observations. These parameters include: (a) the reaction rate between H+ and vibrationally excited H2, (b) an influx of H20 from the top of the atmosphere, (c) a vertical drift caused by neutral winds and/or an E x B drift forcing plasma along magnetic field lines, and (d) a variation in the location of the turbopause.
Support for this work was provided by a grant from the NASA Planetary Atmospheres Program (MM), a NASA Graduate Student Research Proposal grant (LM), and a British Royal Society University Research Fellowship (IMW).
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.