Texture and Composition of Titan's Equatorial Sand Seas Inferred From Cassini SAR Data: Implications for Aeolian Transport and Dune Morphodynamics

• Published in: Journal of geophysical research. Planets 2019-11, Vol.124 (11), p.3140-3163
• Main Authors: Lucas, A., Rodriguez, S., Lemonnier, F., Le Gall, A., MacKenzie, S., Ferrari, C., Paillou, P., Narteau, C.
• Format: Article
• Language: English
• Subjects: Astrophysics; Avalanches; Backscatter; Backscattering; Cassini mission; Chemical properties; climate; Climatic conditions; Composition; Computer simulation; Dielectric constants; Dunes; Earth and Planetary Astrophysics; Equatorial regions; Geological history; Incidence angle; microwave inversion; Modelling; Morphology; Organic chemistry; Permittivity; Physical properties; Physics; Radar; Radar data; Radar imaging; Sand; sand dune; Saturn satellites; Sciences of the Universe; Sediment transport; Sedimentary structures; Surface properties; Synthetic aperture radar; Texture; Titan
• ISSN: 2169-9097; 2169-9100
• DOI: 10.1029/2019JE005965

The texture, composition, and morphology of dunes observed in the equatorial regions of Titan may reflect present and/or past climatic conditions. Determining the physio‐chemical properties and the morphodynamics of Titan's dunes is therefore essential to understanding of the climatic and geological history of the largest moon of Saturn. We quantitatively derived average surface properties of dune and interdune areas (texture and composition) from modeling of the microwave backscattered signal and Monte Carlo inversion of the despeckled Cassini/Synthetic Aperture Radar data over Titan's three largest sand seas: Belet, Shangri‐La, and Fensal. We present the first analysis of the backscatter functions extracted from despeckled Synthetic Aperture Radar images that cover such a large range in incidence angles, including data from the beginning of the Cassini mission up to its Grand Finale. We show that dunes and interdunes have significantly different physical properties. Dunes are found to be more microwave absorbent than interdunes. Additionally, potential secondary bedforms, such as ripples and avalanches, may have been detected, providing potential evidence for currently active dunes and sediment transport. Our modeling shows that the interdunes have multiscale roughnesses with higher dielectric constants than the dunes which have a low dielectric constant consistent with organic sand. The radar brightness of the interdunes can be explained by the presence of a shallow layer of significantly larger organic grains, possibly nonmobilized by the winds. Together, our findings suggest that Titan's sand seas evolve under the current multidirectional wind regimes with dunes that elongate with their crests aligned in the residual drift direction. Key Points Physical properties over Titan sand seas are quantitatively derived from Bayesian inference of the Cassini SAR amplitude data Interdunes terrains are made of fine and coarse parsed grains over polluted water ice bedrock Analogy with terrestrial sand seas in Niger and China suggests that dunes on Titan reflect current climatic conditions