Far Ultraviolet Imaging Spectroscopy of Io's Atmosphere with HST/STIS

Fred L. Roesler, H. Warren Moos, Ronald J. Oliversen, R. Carey Woodward Jr.,* Kurt D. Retherford, Frank Scherb, Melissa A. McGrath, William H. Smyth, Paul D. Feldman, and Darrell F. Strobel

Well-resolved far ultraviolet spectroscopic images of O I, S I, and previously undetected Lyman alpha emission from Io were obtained with the Hubble Space Telescope Imaging Spectrograph (STIS). Detected O I and S I lines (1250-1500Å) have bright equatorial spots (up to 2.5 kilorayleighs) that shift position with jovian magnetic field orientation; limb glow that is brighter on the hemisphere facing the jovian magnetic equator; and faint diffuse emission extending to ~20 Io radii. All O I and S I features brightened by ~50% in the last two images, concurrently with a ground-based observation of increased Iogenic [O I] 6300Å emission. The Lyman alpha emission, consisting of a small, ~2 kilorayleigh patch near each pole, has a different morphology and time variation.

*To whom correspondence should be addressed: woodward@physics.wisc.edu


This article appeared in Science 283, 353-357, 1999. Because of copyright concerns, only the abstract is available on this site; however, the full content and an editorial summary are available to subscribers at the Science website. Reprints may also be requested directly from Carey Woodward at

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