Implications on the composition of Titan's mid-latitude surface region from Cassini/VIMS data.

We investigate the surface of Titan using spectro-imaging near-infrared data from the Cassini Visual and Infrared Mapping Spectrometer (VIMS). We apply a radiative transfer code to first determine the contributions of atmospheric haze to the Titan spectrum and then derive the surface albedo (Solomonidou et al. 2014; 2016). We focus here on the geological major units identified in Lopes et al. (2010, 2016), Malaska et al. (2016) and Radebaugh et al. (2016) from Synthetic Aperture Radar (SAR) data, including mountains, different types of plains, labyrinths, impact craters, dune fields, and alluvial fans. We find that all regions classified as being the same geomorphological unit in SAR exhibit a coherent spectral response after the VIMS data analysis, thus suggesting a good correlation in the classification between SAR and VIMS. The Huygens landing site appears to be compositionally similar to one type of plains unit (variable plains), suggesting similar plain formation mechanisms. We have sub-categorized the VIMS data into three albedo categories (high, medium, low). By matching the extracted albedos with candidate materials for Titan's surface (GhoSST database), we find that all regions of interest fall into one of three main types of major candidate constituents: water ice, or tholin-like material, or an unknown, very dark material. This suggests that Titan's surface is possibly dominated by tholin-like material and a very dark unknown (most likely organic) material, suggesting that most of the surface is covered by atmospheric/organic deposits. Water-ice is also present at a number of regions as major constituent at latitudes higher than 30ºN and lower than 30ºS. The surface albedo differences and similarities among the various geomorphological units constrain the implications for the geological processes that govern Titan's surface and interior (e.g. aeolian, fluvial, sedimentary, lacustrine, cryovolcanic, tectonic). References: Lopes, R.M.C., et al.: Icarus, 205, 540-558, 2010; Lopes, R.M.C., et al.: Icarus, 270, 162-182, 2016; Malaska, M., et al.: Icarus, 270, 130-161, 2016; [4] Solomonidou, A., et al.: JGR, 119, 1729-1747, 2014; [6] Solomonidou, A., et al.: Icarus, 270, 85-99, 2016; [7] Schmitt, B., et al.: GhoSST database (ghosst.osug.fr).