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[13.02] Variability of the SO₂ Atmosphere of Io

L.M. Feaga (JHU/STScI), M.A. McGrath (STScI), P.D. Feldman, D.F. Strobel (JHU)

Io is the most volcanically active body in the solar system and plays an important role in supplying material to the entire Jovian system. A combination of volcanism and sublimation has maintained an atmosphere on Io primarily consisting of SO₂. Analysis of the reflected solar Lyman-\alpha intensities from the disk of Io has proved to be an effective method of mapping the atmospheric SO₂ distribution. It has been shown using HST Space Telescope Imaging Spectrograph (STIS) data that an equatorial SO₂ atmosphere, N ~ 1-4 \times10¹⁶ cm^-2, decreasing to below 10¹⁵ cm^-2 at the poles exists at Io (Feldman et al. 2000, GRL 27, 1787, Strobel & Wolven 2001, Ap & SS 277, 271). Although this general trend is seen in all HST/STIS G140L data of Io acquired from 1997-2001, there are large variations in the Lyman-\alpha intensities at latitudes larger than ±20\arcdeg between dates as well as north/south asymmetries observed in the same exposure. The variability could be due to either temporal changes in the SO₂ atmosphere or spatial differences at Io, in particular the location of surface features and volcanoes. We analyze the Lyman-\alpha signature in a sub-set of the HST/STIS data, in which there are both temporal and longitudinal commonalities, to distinguish between temporal and spatial variations, to quantitatively describe the variations at higher latitudes, and to attempt a correlation between bright surface frosts or volcanic centers and significant spatial variations.

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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.