Characterization of Titan’s Northern Polar Terrains From Inversion of Cassini RADAR Data

We investigated the surface geophysical properties of Titan through a multi-angular backscattering analysis of Cassini Ku-band radar data acquired in altimetry, SAR, scatterometry and radiometry modes. We test quasi-specular scattering models in combination with a volume scattering formulation to model the backscatter coefficient as a function of incidence angle over specific areas identified from topographic and radar imaging data. From data inversion we found that the exponential model provides the best fit to the observed data. We present our results in terms of effective permittivity, surface roughness and volume scattering albedo across different backscattering uniform regions at Titan’s northern hemisphere, where both radar-bright and -dark terrains have been observed from radar images acquired during the mission. Our results indicate that these bright regions belong to a large low-lying plain made of material with a relatively high dielectric constant, high-volume scattering albedo, and moderate wavelength-scale roughness inferred from the model inversion. In contrast, dark regions are consistent with solid hydrocarbons accumulations, reaching thicknesses of up to hundreds of meters above this plain, and they exhibit a lower dielectric constant, lower volume albedo, and slightly higher wavelength-scale surface roughness together with additional higher meter- to tens-of-meter-scale roughness inferred from altimetry. Finally, we propose some of the most probable scenarios based on a list of candidate materials that may be present at the surface of Titan. Although our analysis focuses on a specific, albeit extensive, region near the North Pole, our findings may offer broader insights into the global distribution of complex organics on Titan surface, which are likely superimposed on top of a mixture of ice and organic material.