Galileo Imaging of Atmospheric Emissions from Io
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.
© 1999 American Association for the Advancement of Science. Received 12 March 1999; accepted 24 June 1999. We are grateful for informative discussions with many patient colleagues before and during the Madison, Wisconsin, meeting of the Division for Planetary Sciences of the American Astronomical Society. Particular thanks are due to C. Alexander, F. Bagenal, F. Crary, A. Dessler, F. Herbert, W. Hubbard, D. Hunten, K. Klaasen, L. Lane, M. McGrath, K. Rages, and N. Schneider.