Titan Surface Composition at the Huygens Landing Site from DISR Spectra
Résumé
The Descent Imager/Spectral Radiometer (DISR) aboard the Huygens probe recorded complete visible and near infrared spectra (480-1600 nm) of the surface of Titan near the landing site during the last tens of meters of the descent and from a few tens of centimetres after landing. The surface spectrum has a relatively low albedo, peaking around 0.18 at 830 nm, a red slope in the visible range, a quasi-linear decrease of the reflectivity from 830 to 1420 nm, and displays a broad absorption near 1540 nm. The featureless blue slope of this spectrum above 830 nm is very unusual and has no known equivalent on any other object in the Solar System. In addition no published laboratory data of ices or organic materials displays such a spectral behaviour. Laboratory studies and numerical simulations of the DISR spectrum have been performed to try to understand the nature and composition of the materials constituting the surface of Titan. In particular reflectance spectra over the solar spectrum (300-4000 nm) of several types of tholins and organics have been recorded with the LPG spectro-gonio radiometer. Numerical simulations of the surface reflectance spectrum have been performed in order to constrain the optical properties of the different components (ices, organics, etc) and to infer their composition. We will present the current state of analysis of this spectrum.