37th DPS Meeting, 4-9 September 2005
Session 53 Titan III
Oral, Thursday, September 8, 2005, 4:20-6:00pm, Music Concert Hall

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[53.02] Composition of Titan's Surface from Cassini VIMS

T. B. McCord (Space Science Institute, NW), G. B. Hansen (U. of Wash.), E. D'Aversa (IFSI, CNR), K. H. Baines (JPL), R. H. Brown (Dept. Pl Sci, U. of Az), B. J. Buratti (JPL), R. N. Clark (USGS, Denver), D. P. Cruikshank (NASA Ames Res. Center), G. Filacchione, V. Formisano (IFSI, CNR), C. A. Griffith (Dept. Pl Sci, U. of Az), C. A. Hibbitts (J. Hop. U., APL), R. Jaumann (DLR, Inst. for Pl. Exp.), J. I. Lunine (Dept. Pl. Sci, U. of Az), R. M. Nelson (JPL), L. A. Soderblom (USGS, Flagstaff), C. Sotin (U. of Nantes), Cassini VIMS Team

Titan’s bulk density indicates considerable water as well as silicates as its major constituents. Deposits of organic compounds have been suggested to exist due to UV-induced photochemistry in the atmosphere. However, studies of the surface are hindered by the thick, absorbing, hazy and in some places cloudy atmosphere. Groundbased telescope investigations attempted to observe the surface albedo in spectral windows between methane absorptions by calculating and removing the haze effects. Their results were consistent with water ice on the surface contaminated with a small amount of dark material. Recent Cassini Mission Visual and Infrared Mapping spectrometer (VIMS) observations resolved surface features and shows that there are spectral and therefore likely compositional units. By several methods, spectral albedo estimates within methane absorption windows between 0.75 and 5 µm were obtained for different surface units. Of the spots studies, there appears to be two compositional classes present that are associated with the visually darker and the brighter materials, with more variety among the brighter regions. One region is unusually or uniquely bright at 2.8 and 5 µm. These were compared with spectra of several different candidate materials. Our results suggest that water ice, perhaps contaminated with a darker material that is red in the visual range, matches the reflectance of the Titan regions that are darker in the visual range. The brighter regions studies are not matched by water ice, pure or in mixtures that allow the water ice spectrum to be discerned or by pure or mixed unoxidized tholin. In addition, we find that the 2.8-µm methane absorption window is complex and seems to consist of two weak windows at 2.7 and 2.8 µm.

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