title: Plasma observations at Io with the Galileo spacecraft.
abstract: Plasma measurements made during the flyby of Io on 7 December 1995 with the Galileo spacecraft plasma analyzers reveal that the spacecraft unexpectedly passed directly through the ionosphere of Io. The ionosphere is identified by a dense plasma that is at rest with respect to Io. This plasma is cool relative to those encountered outside the ionosphere. The composition of the ionospheric plasmas includes O++, O+ and S++, S+, and SO2+ ions. The plasma conditions at Io appear to account for the decrease in the magnetic field, without the need to assume that Io has a magnetized interior.
authors.affiliation: Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA.
authors.forename: L A
authors.initials: LA
authors.lastname: Frank
authors.forename: W R
authors.initials: WR
authors.lastname: Paterson
authors.forename: K L
authors.initials: KL
authors.lastname: Ackerson
authors.forename: V M
authors.initials: VM
authors.lastname: Vasyliunas
authors.forename: F V
authors.initials: FV
authors.lastname: Coroniti
authors.forename: S J
authors.initials: SJ
authors.lastname: Bolton
mesh_terms: D005118:Extraterrestrial Environment; D007477:Ions; D018538:Jupiter; D008280:Magnetics; D010100:Oxygen / Q000032:analysis; D013455:Sulfur / Q000032:analysis; D013458:Sulfur Dioxide / Q000032:analysis
chemical_list: D007477:Ions; D013458:Sulfur Dioxide; D013455:Sulfur; D010100:Oxygen