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N.M. Schneider, A.H. Park (CU/LASP), M.E. Kuppers (U. Bern)
We report observations of the Io torus taken with the KPNO 2.1m telescope during Galileo's I24 and I25 Io flyby's. We used a long-slit spectrograph to capture a total of eleven ionic emissions from five species: S+, S++, O+, Cl+ and a new detection of Cl++ at 5518, 5538Å. Neutral sodium and potassion were also observed.
Line ratios between emissions from the same ion species are diagnostic of torus densities and temperatures. We will compare our remote determinations of plasma conditions to Galileo in situ measurements and simultaneous results from HST (Bagenal et al., this meeting). Groundbased spectroscopy from KPNO and simultaneous imaging from Catalina Observatory (Burger et al., this meeting) will provide the best global context for the in situ data.
The discovery of Cl++ emission at a level comparable to Cl+ will increase the total chlorine mixing ratio in the torus above the 2±0.5% estimated from Cl+ alone (Kuppers & Schneider, GRL 27, 513-516, 2000). The resulting higher chlorine mixing ratio will likely be closer to the sodium mixing ratio, though the latter is also poorly determined. Since chlorine's cosmic abundance is 10x lower than sodium's, their comparable values in the Io torus suggest that NaCl is the parent molecule of both.
This work has been supported by NASA's Planetary Astronomy Program and NOAO/KPNO.