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Science 6 August 1999:
Vol. 285. no. 5429, pp. 870 - 874
DOI: 10.1126/science.285.5429.870
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Reports

Galileo Imaging of Atmospheric Emissions from Io

P. E. Geissler, 1* A. S. McEwen, 1 W. Ip, 2 M. J. S. Belton, 3 T. V. Johnson, 4 W. H. Smyth, 5 A. P. Ingersoll 6

The Galileo spacecraft has detected diffuse optical emissions from Io in high-resolution images acquired while the satellite was eclipsed by Jupiter. Three distinct components make up Io's visible emissions. Bright blue glows of more than 300 kilorayleighs emanate from volcanic plumes, probably due to electron impact on molecular sulfur dioxide. Weaker red emissions, possibly due to atomic oxygen, are seen along the limbs, brighter on the pole closest to the plasma torus. A faint green glow appears concentrated on the night side of Io, possibly produced by atomic sodium. Io's disk-averaged emission diminishes with time after entering eclipse, whereas the localized blue glows brighten instead.

1 Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85711, USA.
2 Institute of Astronomy, National Central University, Chung-Li, Taiwan 320, Republic of China.
3 National Optical Astronomy Observatories, Tucson, AZ 85719, USA.
4 Jet Propulsion Laboratory, MS 23-201B, 4800 Oak Grove Drive, Pasadena, CA 91109, USA.
5 Atmospheric and Environmental Research, 840 Memorial Drive, Cambridge, MA 02139, USA.
6 Division of Geology and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.
*   To whom correspondence should be addressed. E-mail: geissler{at}lpl.arizona.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
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Galileo at Io: Results from High-Resolution Imaging.
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