Photoclinometry, Morphometry, and Spectroscopy of Titan's Sand Dunes from Cassini/VIMS

We present results from recent Cassini Visual and Infrared Mapping Spectrometer (VIMS) observations of the sand seas that cover Titan's equatorial region. High-resolution (~500 m/pixel) spectral mapping from the T20 Titan flyby on 2006 October 20 shows the dunes. The dunes themselves, and presumably therefore the sand of which they are comprised, are dark in all of Titan's spectral windows. The spectrum best matches organic material, but a small water-ice component cannot be ruled out. Thus the sand particles cannot be pure water ice but could still be mostly ice by volume but coated by an organic rind at least several microns thick. The dunes are separated by interdunes in some places, but are continuous in others. Where interdunes exist, we are able to map the extent of the substrate units. Where no interdunes exist, we use photoclinometry to ascertain crest-trough-crest heights of between 30 and 70 meters. Dune separations in the T20 observations are just over 2 kilometers from crest to crest; the dunes' orientations are predominantly east-west, but with variations of up to 10 degrees in either direction. A properly designed future VIMS observation would be capable of gathering a resolved profile of the dune slopes to ascertain wind direction and present activity status.