A compositional map for Titan's surface

International audienceThe investigation of Titans surface chemical composition is of great importance for the understanding of the atmosphere-surface-interior system of the moon. The Cassini cameras and especially the Visual and infrared Mapping Spectrometer have provided a sequence of spectra showing the diversity of Titans surface spectrum from flybys performed during the 13 years of Cassinis operation. In the 0.8-5.2m range, this spectro-imaging data showed that the surface consists of a multivariable geological terrain hosting complex geological processes. The data from the seven narrow methane spectral windows centered at 0.93, 1.08, 1.27, 1.59, 2.03, 2.8 and 5m provide some information on the lower atmospheric context and the surface parameters. Nevertheless, atmospheric scattering and absorption need to be clearly evaluated before we can extract the surface properties. In various studies [1-8], we used radiative transfer modeling in order to evaluate the atmospheric scattering and absorption and securely extract the surface albedo of multiple Titan areas including the major geomorphological units. We also investigated the morphological and microwave characteristics of these features using Cassini RADAR data. Here, we present a global map for Titans surface showing the chemical composition constraints for the various units. The results show that Titans surface composition, at the depths detected by VIMS, has significant latitudinal dependence, with its equator being dominated by organic materials from the atmosphere and a very dark unknown material, while higher latitudes contain more water ice. The albedo differences and similarities among the various geomorphological units give insights on the geological processes affecting Titans surface and, by implication, its interior. We discuss our results in terms of origin and evolution theories. References: [1] Solomonidou et al. (2014), JGR-Planets, 119, 1729; [2] Solomonidou et al. (2016), Icarus, 270, 85; [3] Solomonidou et al. (2018), JGR-Planets, 123, 489; [4] Solomonidou et al. (2020a), Icarus, 344, 113338; [5] Solomonidou et al. (2020b), A&A 641, A16; [6] Lopes et al. (2016) Icarus, 270, 162; [7] Malaska et al. (2016), Icarus 270, 130; [8] Malaska et al. (2020), Icarus, 344, 113764