31st Annual Meeting of the DPS, October 1999
Session 78. Io: Neutral Atmosphere, Ionosphere, Magnetospheric Interactions, and Plasma Torus
Contributed Oral Parallel Session, Friday, October 15, 1999, 4:00-5:30pm, Sala Pietro d'Abano

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[78.07] Chlorine on Io

N. M. Schneider (LASP, U. Colorado), M. Kueppers (Inst. of Physics , Univ. of Bern)

We will discuss observations of Cl+ in the Io plasma torus which imply a strong source of chlorine from Io. The observations were performed with the 2.1m telescope at Kitt Peak National Observatory using the GoldCam spectrograph. An emission feature corresponding to the forbidden line of Cl+ at 857.9 nm was detected at the ~6-\sigma level at precisely the predicted wavelength at the spatial location of the torus. The peak intensity of 40 Rayleighs at 857.9 nm corresponds to a Cl+ abundance of ~2% relative to sulfur and oxygen ions, perhaps comparable to sodium. The likely source of Cl+ in the plasma torus are Cl-bearing species in Io's tenuous atmosphere. NaCl in crystalline or gaseous form is probably an important source of both Na and Cl in the vicinity of Io. Although the atmospheric density is low in absolute terms, Io's atmosphere probably has the highest proportion of chlorine of any planetary body. The atmospheric and geological implications of chlorine will be discussed.

This work has been supported by NASA's Planetary Astronomy program. Observations were made at Kitt Peak National Observatory, National Optical Astronomy Observatories, which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation.

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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