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L. M. Feaga (JHU/STScI), M. A. McGrath (STScI), P. D. Feldman, D. F. Strobel (JHU)
As part of a comprehensive analysis of Io's tenuous SO2 atmosphere, we present maps of the SO2 column density distribution with 200 km resolution derived from five years of HST Space Telescope Imaging Spectrograph (STIS) Lyman-\alpha data and investigate the relationship between the column density and surface features, volcanoes, and hot spots. The SO2 atmosphere is maintained by a combination of volcanic output and surface frost sublimation. Although the volcanic contribution may cause a more temporally and spatially variable atmosphere than sublimation, both atmospheric drivers will have some dependence on location and activity of the source regions. It is found that the maximum column density on each of the dates examined is always confined to ±25\arcdeg latitude, while the minimum densities are at higher latitudes. Since the behavior of the SO2 atmosphere may be strongly dependent on the local surface, it is instructive to plot the column densities with surface feature maps from Voyager and Galileo noting the volcanic locations and frost fields. Although we have assumed a constant albedo for this analysis, the comparisons made here between the SO2 atmosphere and the surface material and features lay the foundation for future modeling which will be albedo dependent. Recurring correlations will constrain the albedo. Future work will consist of modeling the albedo and column densities simultaneously, deriving surface temperatures from the column densities, and correlating the temperatures to the surface features.
Support for this work was provided by NASA through grant number HST-AR-10313.02-A from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.