The Atmosphere of Io: Abundances and Sources of Sulfur Dioxide and Atomic Hydrogen

  • Darrell F. Strobel
  • Brian C. Wolven
Conference paper


An analysis and interpretation of reflected solar Lyman α intensity data acquired with the Hubble Space Telescope (HST) implies an equatorially confined atmosphere with SO2 column densities ∼ 1−2 × 1016 cm−2. Poleward of 30° the SO2 density must decrease sharply reaching an asymptotic polar value of < 1015 cm−2 at 45° to achieve the observed 2 kR intensity peaks. The corresponding surface reflectivities must be either a constant 0.047 for higher equatorial SO2 or a variable reflectivity of 0.027 with lower SO2 densities at the equator increasing to a polar value of ∼ 0.05. The average residence time for an atmospheric SO2 molecule is ∼ 2–3 days for the canonical mass loading rate of the Io plasma torus = 1030 amu s−l. With atomic hydrogen in the atmosphere and corona constrained by the HST observations, it is estimated that a pickup proton density ratio of 0.25–0.4% can be sustained by a supply of Io plasma torus protons neutralized in Io’s atmosphere/exosphere, if protons constitute 7% of the total torus ion density, which is close to the Chust et al. (1999) pickup proton density ratio and under the widely quoted 10% proton content of the torus.


Column Density Hubble Space Telescope Geometric Albedo Pickup Proton Charge Exchange Cross Section 
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Copyright information

© Springer Science+Business Media New York 2001

Authors and Affiliations

  • Darrell F. Strobel
    • 1
    • 2
  • Brian C. Wolven
    • 2
  1. 1.Department of Earth and Planetary SciencesThe Johns Hopkins UniversityBaltimoreUSA
  2. 2.Department of Physics and AstronomyThe Johns Hopkins UniversityBaltimoreUSA

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