F. Leader

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 are presented here. SO2, existing as a frost, is found almost everywhere, but with spatially variable concentration. The exceptions are volcanic hot spots, where high surface temperatures promote rapid vaporization and can produce SO2-free areas. The pervasive frost, if fully covering the cold surface, has characteristic grain sizes of 30 to 100 µm, or greater. Regions of greater sulfur dioxide concentrations are found. The equatorial Colchis Regio area exhibits extensive snowfields with large particles (250 to 500 µm diameter, or greater) beneath smaller particles. A weak feature at 3.15 µm is observed and is perhaps due to hydroxides, hydrates, or water. A broad absorption in the 1 µm region, which could be caused by iron-containing minerals, shows a concentration in Ios southern polar region, with an absence in the Pele plume deposition ring.

Hot spots on Io: Initial results from Galileo's near infrared mapping spectrometer

The Near-Infrared Mapping Spectrometer on Galileo has monitored the volcanic activity on Io since June 28, 1996. This paper presents preliminary analysis of NIMS thermal data for the first four orbits of the Galileo mission. NIMS has detected 18 new hot spots and 12 others which were previously known to be active. The distribution of the hot spots on Ios surface may not be random, as hot spots surround the two bright, SO2-rich regions of Bosphorus Regio and Colchis Regio. Most hot spots seem to be persistently active from orbit to orbit and 10 of those detected were active in 1979 during the Voyager encounters. We report the distribution of hot spot temperatures and find that they are consistent with silicate volcanism.