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Distribution of icy particles across Enceladus' surface as derived from Cassini-VIMS measurements |
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| Authors: | R Jaumann K Stephan RN Clark RH Brown SF Newman G Filacchione DP Cruikshank CA Hibbitts RM Nelson C Sotin |
| Institution: | a DLR, Institute of Planetary Research, Rutherfordstrasse 2, 12489 Berlin, Germany b Department of Earth Sciences, Institute of Geosciences, Free University, Berlin, Germany c Bear Fight Center, 22 Fiddler's Rd., Winthrop, WA 98862-0667, USA d US Geological Survey, Denver Federal Center, Denver, CO 80225, USA e Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA f Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA g Istituto Fisica Spazio Interplanetario, CNR, Via Fosso del Cavaliere, Roma, Italy h NASA Ames Research Center, 245-6, Moffett Field, CA 94035-1000, USA i Department of Astronomy, Cornell University, Ithaca, NY 14853, USA j University of Nantes, 44072 Nantes Cedex 3, France |
| Abstract: | The surface of Enceladus consists almost completely of water ice. As the band depths of water ice absorptions are sensitive to the size of particles, absorptions can be used to map variations of icy particles across the surface. The Visual and Infrared Mapping Spectrometer (VIMS) observed Enceladus with a high spatial resolution during three Cassini flybys in 2005 (orbits EN 003, EN 004 and EN 011). Based on these data we measured the band depths of water ice absorptions at 1.04, 1.25, 1.5, and 2 μm. These band depths were compared to water ice models that represent theoretically calculated reflectance spectra for a range of particle diameters between 2 μm and 1 mm. The agreement between the experimental (VIMS) and model values supports the assumption that pure water ice characterizes the surface of Enceladus and therefore that variations in band depth correspond to variations in water ice particle diameters. Our measurements show that the particle diameter of water ice increases toward younger tectonically altered surface units with the largest particles exposed in relatively “fresh” surface material. The smallest particles were generally found in old densely cratered terrains. The largest particles (∼0.2 mm) are concentrated in the so called “tiger stripes” at the south pole. In general, the particle diameters are strongly correlated with geologic features and surface ages, indicating a stratigraphic evolution of the surface that is caused by cryovolcanic resurfacing and impact gardening. |
| Keywords: | Enceladus Saturn satellites |
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