ELECTRON-BEAMS AND ION COMPOSITION MEASURED AT IO AND IN ITS TORUS

Intense, magnetic field-aligned, bidirectional, energetic (>15 kiloele ctron volts) electron beams were discovered by the Galileo energetic p articles detector during the flyby of Io. These beams can carry suffic ient energy flux into Jupiter's atmosphere to produce a visible aurora at the footprint of the magnetic flux tube connecting Io to Jupiter. Composition measurements through the torus showed that the spatial dis tributions of protons, oxygen, and sulfur are different, with sulfur b eing the dominant energetic (>similar to 10 kiloelectron volts per nuc leon) ion at closest approach.