Extreme Ultraviolet Observations from Voyager 1 Encounter with Jupiter

Abstract

Observations of the optical extreme ultraviolet spectrum of the Jupiter planetary system during the Voyager 1 encounter have revealed previously undetected physical processes of significant proportions. Bright emission lines of S III, S IV, and O III indicating an electron temperature of 10(5) K have been identified in preliminary analyses of the Io plasma torus spectrum. Strong auroral atomic and molecular hydrogen emissions have been observed in the polar regions of Jupiter near magnetic field lines that map the torus into the atmosphere of Jupiter. The observed resonance scattering of solar hydrogen Lyman alpha by the atmosphere of Jupiter and the solar occultation experiment suggest a hot thermosphere (>/= 1000 K) wvith a large atomic hydrogen abundance. A stellar occultation by Ganymede indicates that its atmosphere is at most an exosphere.

Survey of thermal ions in the Io plasma torus with the Galileo spacecraft

“…The early Voyager I optical survey [Broadfoot et al, 1979] and this spacecraft's in situ plasma measurements [Bridge et al, 1979] clearly established that heavy ions such as those of oxygen and sulfur are major constituents of the plasma torus. The source is provided by the remarkable volcanic activity of Io.…”

“…The next major milestones in the detection of the plasmas in the vicinity of Io and its orbit around Jupiter were gained during the fiybys of this planet by the Voyager I and 2 spacecraft. Observations of the ultraviolet and visible spectra with the onboard spectrometer established that Jupiter was encompassed by a torus of heavy ions such as those of oxygen and sulfur in several charge states [Broadfoot et al, 1979]. Indeed, these ions were directly measured by the plasma analyzer on board Voyager I as it passed through the plasma torus [Bridge et al, 1979].…”

Control of Jupiter's radio emission and aurorae by the solar wind

“…Jupiter also has polar aurorae 4 , which are similar in many respects to Earth's aurorae 5 . The radio emissions are believed to be generated along the high-latitude magnetic ®eld lines by the same electrons that produce the aurorae, and both the radio emission in the hectometric frequency range and the aurorae vary considerably 6,7 .…”

Hubble Space Telescope observations of sulfur ions in the Io plasma torus: New constraints on the plasma distribution

“…Though first detected by ground-based observations [Kupo et al, 1976], much of what we know of the torus resulted from extensive observations, both remote and in situ, by the Voyager spacecraft [e.g., Broadfoot et al, 1979;Bagenal and Sullivan, 1981;Broadfoot, 1982a, 1982b;Sittler and Strobel, 1987]. Since that era, visible-wavelength observations from the ground [e.g., Morgan, 1985;Brown, 1995;Schneider and Trauger, 1995;Thomas et al, 2001] and ultraviolet spectroscopy from Earth's orbit [e.g., Moos et al, 1985Moos et al, , 1991Hall et al, 1994;Herbert et al, 2001;Feldman et al, 2001] have broadened our understanding of this still enigmatic object.…”

“…These spatial and temporal variations are presumably clues to torus maintenance processes. Many authors [e.g., Sandel and Dessler, 1988;Brown, 1994Brown, , 1995Schneider et al, 1997;Herbert and Sandel, 1995;Thomas, 1995;Herbert and Sandel, 2000;Herbert et al, 2001] have used these properties to constrain the nature of torus processes. We follow the same approach in this paper.…”