Some Aspects of Io's surface Composition from Galileo Near-Infrared Spectral Mapping. Spectral Mapping of Io is being conducted using the Near Infrared Mapping Spectrometer on Galileo, and data from several orbits covering a year's observations are being analyzed to determine the spatial and temporal characteristics of the surface composition. Early results for the anti-Jovian hemisphere show that sulfur dioxide frost occurs almost everywhere, agreeing with Howell et al.
Exceptions are the hot volcanic regions, where high surface temperatures promote rapid vaporization.
The pervasive frost coating, if fully covering the cold surface, has grain sizes of 30 to 100 microns, or greater. Regions of high sulfur dioxide concentrations are found. A weak feature at 3.15 microns is observed and could arise from hydroxides, hydrates, water, or others. A broad feature in the 1 micron region, perhaps due to iron-containing minerals, shows enhanced concentration in Io's southern polar region, and an absence in the Pele plume deposition ring. Spatial distribution and physical state, Icarus 57, 83-92, 1984.