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Published November 2000 | public
Journal Article

Eclipse Spectroscopy of Io's Atmosphere


High resolution optical (4193–6619 Å) spectra of Io in eclipse show auroral emission in five lines: [Oi] 6300, 6363, 5577 Å and Na 5889, 5896 Å. We conclude that Io's diffuse red emissions imaged by the Galileo Solid State Imager (P. E. Geissler et al. 1999, Science 285, 870–874) are due to impact or dissociative excitation of oxygen, while diffuse green emissions are caused by the impact or dissociative excitation of sodium. No emission lines were detected in the blue region of the spectra, suggesting that the intense emission observed above Io's equatorial plumes is due to a molecular species such as SO_2 or SO.

Additional Information

© 2000 Academic Press. Received January 31, 2000; revised August 18, 2000. We thank Teresa Chelminiak, Barbara Schaefer, and David Sprayberry for assistance with these difficult observations, K.L. Bell for supplying oxygen cross sections, and Paul Geissler and an anonymous reviewer for helpful suggestions on the manuscript. A.H.B. is supported by an NSF graduate research fellowship. The data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation.

Additional details

August 22, 2023
October 19, 2023