THE DISTRIBUTION OF SULFUR-DIOXIDE AND OTHER INFRARED ABSORBERS ON THE SURFACE OF IO

The Galileo Near Infrared Mapping Spectrometer was used to investigate the distribution and properties of sulfur dioxide over the surface of Io, and qualitative results for the anti-Jove hemisphere sue presente d here. SO2, existing as a frost, is found almost everywhere, but with spatially variable concentration. The exceptions are volcanic hot spo ts, where high surface temperatures promote rapid vaporization and can produce SO2-free areas. The pervasive frost, if fully covering the co ld surface, has characteristic grain sizes of 30 to 100 mu m, or great er. Regions of greater sulfur dioxide concentrations are found. The eq uatorial Colchis Regio area exhibits extensive snowfields with large p articles (250 to 500 mu m diameter, or greater) beneath smaller partic les. A weak feature at 3.15 mu m is observed and is perhaps due to hyd roxides, hydrates, or water. A broad absorption in the 1 mu m region, which could be caused by iron-containing minerals, shows a concentrati on in Io's southern polar region, with an absence in the Pele plume de position ring.