The Atmosphere of Io: Abundances and Sources of Sulfur Dioxide and Atomic Hydrogen
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.
KeywordsColumn Density Hubble Space Telescope Geometric Albedo Pickup Proton Charge Exchange Cross Section
Unable to display preview. Download preview PDF.
- Chamberlain, J.W. and Hunten, D.M.: 1987, Theory of Planetary Atmospheres, 2nd edition, pp. 160–225, Academic Press, Orlando.Google Scholar
- Crary, F.J., Bagenal, F., Ansher, J.A., Gurnett, D.A. and Kurth, W.S.: Anisotropy and proton density in the Io plasma torus derived from whistler wave dispersion, J. Geophys. Res. 101, 2699–2706.Google Scholar
- Harris, D.L.: 1961, Photometry and colorimetry of planets and satellites, in: G.P. Kuiper and B.M. Middlehurst (eds.), Planets and Satellites, pp. 272–340, U. of Chicago Press, Chicago.Google Scholar
- Johnson, T.V, Matson, D.L., Blaney, D.L., Veeder, G.J. and Davies, A.G.: 1995, Stealth plumes on Io, Geophys. Res. Lett. 22, 23–26.Google Scholar
- Keiffer, S.W.: 1982, Dynamics and thermodynamics of volcanic eruptions: Implications for the plumes of Io, in: D. Morrison (ed.), Satellites of Jupiter, pp. 647–723, U. Arizona Press, Tucson.Google Scholar
- Strom, R.G. and Schneider, N.M.: 1982, Volcanic eruption plumes of Io. in: D. Morrison (ed.), Satellites of Jupiter, pp. 598–633, U. Arizona Press, Tucson.Google Scholar