The Distribution of Sulfur Dioxide and Other Infrared Adsorbers on the Surface of Io from Galileo NIMS

R.W. Carlson, W.D. Smythe, R.M.C. Lopes-Gautier, A.G. Davies, L.W. Kamp, J.A. Mosher (JPL-Caltech), L.A. Soderblom (USGS-Flagstaff), F.E. Leader, R. Mehlman (UCLA), R.N. Clark (USGS-Denver)

The Galileo Near Infrared Mapping Spectrometer (NIMS) was used to investigate the distribution and relative particle size variations of sulfur dioxide over one hemisphere of Io, centered at 210 tex2html_wrap_inline13 W. Using bands of differing strength, we find that large SO tex2html_wrap_inline15 grains (diameter of order 500 tex2html_wrap_inline17 m) are prevalent in the equatorial region of Colchis Regio and that smaller-sized particles occur almost everywhere, but with spatially variable concentrations. The exception is volcanic hot spots, where high surface temperatures promote rapid vaporization and produce SO tex2html_wrap_inline15 -free areas. The high-latitude abundance of total sulfur dioxide exceeds that found in equatorial regions. A feature at 3.15 tex2html_wrap_inline17 m, perhaps due to an O-H stretch transition, is equatorially distributed and similiarly absent in hot spots. A broad adsorption in the 1 tex2html_wrap_inline17 m region, which may be produced by iron-containing silicates, shows a concentration at Io's southern polar region, with an absence in the Pele plume deposition ring.