Titan's 'blandlands': Are they massive sand sheets?
Résumé
The undifferentiated plains first mapped by Lopes et. al. (2010, Icarus 205) are vast expanses of terrains that appear bland in Cassini RADAR Synthetic Aperture Radar images, hence the designation 'blandlands'. While the interpretation of several other geologic units on Titan, such as dunes and well-preserved impact craters, has been relatively straightforward, the origin of the 'blandlands' has remained mysterious. SAR images show that the 'blandlands' are mostly found at mid-latitudes and appear relatively featureless at radar wavelengths, with no significant topography. Their gradational boundaries and paucity of features in SAR data make geologic interpretation particularly challenging. We have mapped the distribution of these terrains using SAR swaths up to T92, which cover > 50% of Titan's surface. We compared SAR images with their de-noised counterparts (Lucas et. al.,2001, AGU Fall Meeting), the topography using SARTopo method (Stiles et. al., 2009, Icarus 202) and, where possible, the response from radiometry. We examined and evaluated different formation mechanisms. Previous work (Lopes et. al., AGU, 2012) proposed that plains were either (i) sedimentary in origin, resulting from fluvial or lacustrine deposition or accumulation of photolysis products created in the upper atmosphere or (ii) cryovolcanic in origin, consisting of overlapping flows of low relief, obscured by accumulation of sediments. The results from our analysis suggest that the sedimentary origin is the most likely, and that plains materials are similar or the same as dune materials. Plains occur mostly at mid-latitudes, while dunes occur mostly at low latitudes. This may be a result of wind patterns, decrease in sand supply, or changes in properties of sand, perhaps moisture content, all of which would inhibit the formation of large dunes.