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K. Stephan, R. Jaumann (DLR), C.A. Hibbitts, G.B. Hansen (PSI)
During the Galileo Mission Ganymede, one of the icy Galilean satellites was observed with the Near Infrared Mapping Spectrometer (NIMS) and the Solid State Imaging System (SSI). NIMS observed the satellite in the spectral range between 0.7 and 5µm with spatial resolutions up to 3 km/pixel. A detailed analysis of spectral variations across the surface of Jupiter’s satellite Gany-mede included relationships between the well known absorption bands of water ice at 1.04, 1.25, 1.5 and 2 microns. Images acquired by SSI with spatial resolutions up to 50 times better than NIMS provided the geomorphological context of the study. The ratios of the measured band depths reveals global differences, which cannot be explained by compositional changes. In, gen-eral ratio variations show relatively low values in the equatorial regions and increase in the direc-tion toward the poles. Additionally, secondary regional variations were recognized in regions which are located either within the polar or the equatorial regions. Highest values were measured in the vicinity of geomorphological fresh impact craters, which are independent of the location and composition of the crater material. Both the global and regional variations are connected to variations in the particle size of water ice. Relative high values correlate with polar regions where energetic particles of Jupiter’s magnetosphere impact the surface of Ganymede resulting in sputtering of water ice and redepositing fine grained ice as frost in the polar regions. Equatorial regions are protected from this effect due to Ganymede’s own magnetic field and exhibit larger particle sizes than the polar regions (Hansen, 1998). At regional scale impact craters seem to ex-hibit finer particles compared to their surroundings, which agrees with the excavation of fresh material due to impacts on Ganymede.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.