DPS 34th Meeting, October 2002
Session 35. Outer Planet Satellites (other than Titan)
Poster, Chair(s): , Thursday, October 10, 2002, 4:00-6:30pm, Exhibit Hall

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[35.04] Space Weather in the Io Plasma Torus

F. Herbert (LPL, U. Arizona), G.R. Gladstone (SW Research Inst.)

Because many torus phenomena are difficult to observe, many aspects of torus dynamics, mass supply, chemistry, and energization are poorly constrained, despite extensive theoretical modeling. One feature of torus data hitherto underexploited for constraining these issues is time variation. Ion and electron heating, ion chemical reactions, and different modes of transport all have characteristic time delays resulting from their individual finite rates of action. These delays are made observable by fluctuations of torus inputs, that produce a cascade of time variations, and so can be estimated using time series analysis. System periodicities (such as Io's orbital and Jupiter's rotational period) can also be exploited to determine connections with torus mass and energy sources.

Therefore, we have analyzed time variations in Extreme Ultraviolet Explorer (EUVE) observations of the torus made during 1996 and 1999. Preliminary results indicate that S+ varies most strongly at the frequency of Io crossing the torus midplane, suggesting significant ionization of near-Io neutrals by the torus. We also see rapid variation of S+ and slow variation of its ionization product S++, implying slow ionization of S+ and slow transport loss. Moreover, an apparent time-correlation of O+ with S+ suggests a common source such as SO or SO2.

Work is continuing on the full 1993 - 1999 EUVE data archive, expanding the timescales sampled to both longer (\leq 6~yr) and shorter (\geq 1.5~hr) periods. Issues that may potentially be constrained include electron energization, ion chemistry, mass loading, and transport. Other data archives with extensive sampling that could be exploited include those of IUE, Voyager UVS, Cassini UVIS, and ground-based observations.

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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.