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F. Bagenal, P. Delamere, A. J. Steffl (U of Colorado)
Observations of ultraviolet (UV) emissions from the major ion species (S+, S++,S+++,O+,O++) of the Io plasma torus made during the Cassini flyby (October 2000-March 2001) have revealed significant time variability. Using a model for mass and energy flow in the torus parameterized by five input variables (transport timescale, neutral source strength, ratio of oxygen to sulfur atoms in the source, fraction of superthermal electrons, and temperature of the hot electrons), we have investigated the time variability of the torus properties (density, composition and temperature) during the Cassini era. In order to match the changes in emissions, the model suggests that a significant change in the neutral source occurred near the beginning of the observing period, decreasing from >1.8 tons/s to 0.7 tons/s. The changes in the neutral source appear to coincide with the declining phase of a dramatic (i.e. 2-3 order of magnitude) peak in iogenic dust emissions observed by Galileo prior to the Cassini era [Krueger et al., 2003]. Our preliminary studies of torus variability were based on a homogeneous model in order to explore the effects of source and transport variables on the torus chemistry and energetics (Delamere and Bagenal 2003, Delamere et al. 2004). We have extended the model to accommodate variations with latitude and in radial transport.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.