Radar Observations of Titan's Hydrocarbon Seas and Lakes: Refining Liquid Composition and Seafloor Properties

Introduction: The Cassini RADAR altimeter enabled the first direct bathymetric measurements of an extraterrestrial sea by sounding liquid hydrocarbon bodies on Titan. These observations revealed that Titan’s seas are remarkably transparent at Ku-band frequencies with depths that can reach several hundreds of meters. Measurements of the electromagnetic properties of the liquids further indicated a methane-dominated composition, with minor contributions from ethane and nitrogen [1]. Together, these results provided robust quantitative constraints on Titan’s hydrocarbon inventory and on the dielectric properties of its surface liquids.

More recently, re-analyses of Cassini Synthetic Aperture Radar (SAR) observations using multi-angular scattering models have independently characterized the dielectric and roughness properties of solid terrains in Titan’s north polar region. This study revealed systematic differences between radar-bright and radar-dark surface units, providing new insights into compositional and morphological heterogeneity across Titan’s polar regions [2].

Seafloor–Surface Scattering Comparison and Liquid Loss Tangent Refinement: In this work, we directly compare the radar backscattering properties of Titan’s seafloors, inferred from combined Cassini RADAR altimetry and SAR observations, with those of exposed solid surfaces characterized through multi-angular scattering analyses. This combined approach enables improved isolation of attenuation effects associated with the overlying liquid column, allowing refinement estimates of the liquid loss tangent, and improved constraints on the dielectric properties of the underlying seafloor. Particular emphasis is placed on Ligeia Mare, for which we derive an independent estimate of the liquid loss tangent using SAR data, yielding to a more accurate electromagnetic characterization of Titan’s second-largest hydrocarbon sea.

Figure 1. Synthetic Aperture Radar (SAR) mosaic of Titan’s northern polar region showing the distribution and morphology of liquid-filled basins and channels. Yellow lines highlight the major liquid bodies, Figure adapted from [3].

 

Acknowledgements: This work was supported by Italian Space Agency (ASI), contract 2025-4-U.0

References:

[1] Mastrogiuseppe, M., Poggiali, V., Hayes, A., Lorenz, R., Lunine, J., Picardi, G., ... & Zebker, H. (2014). The bathymetry of a Titan sea. Geophysical Research Letters, 41(5), 1432-1437.

[2] M. Mastrogiuseppe et al., "Characterization of Titan’s Northern Polar Terrains From Inversion of Cassini RADAR Data," in IEEE Transactions on Geoscience and Remote Sensing, vol. 64, pp. 1-17, 2026, Art no. 4500117, doi: 10.1109/TGRS.2025.3647365.

[3] Mastrogiuseppe, M., Poggiali, V., Hayes, A.G. et al. Deep and methane-rich lakes on Titan. Nat Astron 3, 535–542 (2019). https://doi.org/10.1038/s41550-019-0714-2