EUVE Observations of the Io Plasma Torus

The first observation of Jupiter using the Long Wavelength detector of the Extreme Ultraviolet Explorer satellite shows a rich emission spectrum from the Io plasma torus. At least 12 features between 350 and 750 Angstroms are apparent in the 59,000 second exposure obtained on March 30 and April 1, 1993. Several lie below the short wavelength cutoff of the Voyager spacecraft UV instruments, and have not been observed previously. Preliminary analysis of the raw detector image identifies most of the features as multiplets of oxygen and sulfur ions. The emissions are spatially resolved along the long dimension of Io's projected orbital ellipse, with the brightest located approximately at each ansa of Io's orbit. Most of the ansa emissions show a distinct dawn/dusk asymmetry.