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N.M Schneider, S.J. Robbins, P.A. Delamere (CU/LASP), A.J. Steffl (SWRI/Boulder)
We report on observational and theoretical studies of ion temperature in the Io plasma torus. Ion temperature is a critical factor for two reasons. First, ions are a major supplier of energy to the torus electrons which power the intense EUV emissions. Second, ion temperature determines the vertical extent of plasma along field lines. Higher temperatures spreads plasma out, lowers the density and slows reaction rates. The combined effects can play a controlling role in torus energetics and chemistry.
An unexpected tool for the study of ion temperature is the longitudinal structure in the plasma torus which often manifests itself as periodic brightness variations. Opposite sides of the torus (especially magnetic longitudes 20 and 200 degrees) have been observed on numerous occasions to have dramatically different brightness, density, composition, ionization state, electron temperature and ion temperature. These asymmetries must ultimately be driven by different energy flows on the opposite sides, presenting an opportunity to observe key torus processes operating under different conditions.
The most comprehensive dataset for the study of longitudinal variations was obtained by the Cassini UVIS instrument during its Jupiter flyby. Steffl (Ph.D. thesis, 2005) identified longitudinal variations in all the quantities listed above with the exception of ion temperatures. We extend his work by undertaking the first search for such variation in the UVIS dataset. We also report on a "square centimeter" model of the torus, which extends the traditional "cubic centimeter" models by including the controlling effects of ion temperature more completely.
This work has been supported by NSF's Planetary Astronomy program.
The author(s) of this abstract have provided an email address for comments about the abstract: nick.schneider@lasp.colorado.edu
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.