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[35.09] Moderate-Resolution EUV Spectra of the Io Plasma Torus During the Galileo I24 Visit

F. Herbert (U. of Arizona), G. R. Gladstone (SWRI)

Spectral images of the Io plasma torus from about 165 hours of observation by the Extreme Ultraviolet Explorer (EUVE) spacecraft were analyzed by a spectral-resolution-enhancing deconvolution algorithm in order to estimate averaged torus properties during Galileo's I24 torus encounter and also in June, 1996. Because of our analysis' improved spectral resolution (\Delta\lambda\approx1 to 2\thinspaceÅ), we are able to separate lines arising from different ion species better than in earlier studies. Here we estimate emission-weighted whole-torus averages of electron temperature and ion fraction.

Comparing the 1996 and I24 observations, the torus electrons were hotter (5.5±.5 vs 4.6±.3\thinspace eV), the torus was brighter (2.9 vs 1.9\times10¹¹\thinspace W over 350\leq\lambda\leq735\thinspaceÅ), and the sulfur/oxygen ratio was higher (0.8 vs 0.55) in the earlier epoch. When separately analyzing the dawn and dusk halves of the torus during I24, we estimate that the dusk half is a few tenths of an eV hotter than at dawn. In our presentation, we will discuss analysis of the data by System III longitude and orbital phase relative to Io.

We have also put new constraints on the values of electron impact collision line strengths for many EUV lines in the range 350\leq\lambda\leq735\thinspaceÅ\ that are of interest for understanding the torus and other sulfur and oxygen plasmas. These numbers are useful for modeling EUV torus spectra at both moderate and low spectral resolution.

This work was supported by the NASA Planetary Atmospheres, Planetary Magnetospheres, and JSDAP programs.

The author(s) of this abstract have provided an email address for comments about the abstract: herbert@vega.LPL.arizona.edu