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K. D. Retherford, H. W. Moos, P. D. Feldman, D. F. Strobel (JHU), M. A. McGrath (STScI), F. L. Roesler (U. Wisconsin)
Quasi-monochromatic images of UV emissions from Io's atmosphere were obtained by the Space Telescope Imaging Spectrograph (STIS) in fall of 1997 and again in August 1998. The emission features can be characterized as consisting of bright spots, a limb glow, and a more extended neutral corona. They are also consistent with those found in images obtained by Galileo/SSI and HST/WFPC2. The bright spots are localized regions of emission roughly associated with Io's sub- and anti-jovian points. The limb glow feature is a thin layer of emission that partially outlines the disk of Io and is presumably due to limb brightening of atmospheric oxygen and sulfur emissions. The series of images show the bright spots changing in Io-centric latitude in a way that follows the changing orientation of the Jovian magnetic field. The extended emission falls off as 1/r out ~20 RIo. Observations with medium-resolution (higher dispersion) spectroscopic modes will be discussed in detail.
The author(s) of this abstract have provided an email address for comments about the abstract: reth@pha.jhu.edu