F. L. Roesler, H. W. Moos, R. J. Oliversen, R. C. Woodward Jr., ^* K. D. Retherford, F. Scherb, M. A. McGrath, W. H. Smyth, P. D. Feldman, D. F. Strobel

Well-resolved far-ultraviolet spectroscopic images of O I, S I, and previously undetected H I Lyman- emission from Io were obtained with the Hubble space telescope imaging spectrograph (STIS). Detected O I and S I lines (1250 to 1500 angstroms) 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 percent in the last two images, concurrently with a ground-based observation of increased iogenic [O I] 6300-angstrom emission. The H I Lyman- emission, consisting of a small, ~2-kilorayleigh patch near each pole, has a different morphology and time variation.

F. L. Roesler, R. C. Woodward Jr., and F. Scherb are in the Physics Department, University of Wisconsin, 1150 University Avenue, Madison, WI 53706, USA. H. W. Moos, K. D. Retherford, and P. D. Feldman are in the Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA. R. J. Oliversen is in the Laboratory for Astronomy and Solar Physics, NASA-Goddard Space Flight Center, Greenbelt, MD 20771, USA. M. A. McGrath is at the Space Telescope Science Institute, Baltimore, MD 21218, USA. W. H. Smyth is with Atmospheric and Environmental Research, Cambridge, MA 02139, USA. D. F. Strobel is in the Department of Earth and Planetary Science, Johns Hopkins University, Baltimore, MD 21218, USA.
^*   To whom correspondence should be addressed.