The spectral nature of Titan's major geomorphological surface units: constraints on the composition

Anezina Solomonidou (1, 2) , Athena Coustenis (3) , Rosaly Lopes (2) , Michael Malaska (2) , Sébastien Rodriguez (4) , Pierre Drossart (3) , Charles Elachi (2) , Bernard Schmitt (5) , Alice Le Gall (6) , Stephen Wall (2) , Kenneth Lawrence (2) , Nico Altobelli (1) , Olivier Witasse (7) , Jani Radebaugh (8) , Ashley Shoenfeld (9)

1 ESAC - European Space Astronomy Centre
2 JPL - Jet Propulsion Laboratory
3 LESIA (UMR_8109) - Laboratoire d'études spatiales et d'instrumentation en astrophysique
4 AIM (UMR7158 / UMR_E_9005 / UM_112) - Astrophysique Interprétation Modélisation
5 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble
6 PLANETO - LATMOS
7 RSSD - Research and Scientific Support Department, ESTEC
8 Department of Geological Sciences [BYU]
9 EPSS - Department of Earth, Planetary and Space Sciences [Los Angeles]

We investigate Titan's low-latitude and midlatitude surface using spectro-imaging near-infrared data from Cassini/Visual and Infrared Mapping Spectrometer. We use a radiative transfer code to first evaluate atmospheric contributions and then extract the haze and the surface albedo values of major geomorphological units identified in Cassini Synthetic Aperture Radar data, which exhibit quite similar spectral response to the Visual and Infrared Mapping Spectrometer data. We have identified three main categories of albedo values and spectral shapes, indicating significant differences in the composition among the various areas. We compare with linear mixtures of three components (water ice, tholin-like, and a dark material) at different grain sizes. Our fits of the data are overall successful, except in some cases at 0.94, 2.03, and 2.79 μm, indicative of the limitations of our simplistic compositional model and the need for additional components to reproduce Titan's complex surface. Our results show a latitudinal dependence of Titan's surface composition, with water ice being the major constituent at latitudes beyond 30°N and 30°S, while Titan's equatorial region appears to be dominated partly by a tholin-like or by a very dark unknown material. The albedo differences and similarities among the various geomorphological units give insights on the geological processes affecting Titan's surface and, by implication, its interior. We discuss our results in terms of origin and evolution theories.

Domaines: Planète et Univers [physics]

Anezina Solomonidou, Athena Coustenis, Rosaly Lopes, Michael Malaska, Sébastien Rodriguez, et al.. The spectral nature of Titan's major geomorphological surface units: constraints on the composition. European Planetary Science Congress 2018, Sep 2018, Berlin, Germany. pp.EPSC2018-167. ⟨hal-02358242⟩