title: Electron beams and ion composition measured at Io and in its torus.
abstract: Intense, magnetic field-aligned, bidirectional, energetic (>15 kiloelectron volts) electron beams were discovered by the Galileo energetic particles detector during the flyby of Io. These beams can carry sufficient 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 distributions of protons, oxygen, and sulfur are different, with sulfur being the dominant energetic (> approximately 10 kiloelectron volts per nucleon) ion at closest approach.
authors.affiliation: Johns Hopkins Applied Physics Laboratory, Johns Hopkins Road, Laurel, MD 20723, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Williams
authors.forename: B H
authors.initials: BH
authors.lastname: Mauk
authors.forename: R E
authors.initials: RE
authors.lastname: McEntire
authors.forename: E C
authors.initials: EC
authors.lastname: Roelof
authors.forename: T P
authors.initials: TP
authors.lastname: Armstrong
authors.forename: B
authors.initials: B
authors.lastname: Wilken
authors.forename: J G
authors.initials: JG
authors.lastname: Roederer
authors.forename: S M
authors.initials: SM
authors.lastname: Krimigis
authors.forename: T A
authors.initials: TA
authors.lastname: Fritz
authors.forename: L J
authors.initials: LJ
authors.lastname: Lanzerotti
mesh_terms: D004583:Electrons; D005118:Extraterrestrial Environment; D007477:Ions; D018538:Jupiter; D008280:Magnetics; D010100:Oxygen / Q000032:analysis; D011522:Protons; D013455:Sulfur / Q000032:analysis
chemical_list: D007477:Ions; D011522:Protons; D013455:Sulfur; D010100:Oxygen