Session 39. Titan I
Contributed Oral Parallel Session, Thursday, October 15, 1998, 10:40-11:40am, Madison Ballroom D

## [39.03] Spectroscopy of Titan in the near-IR: modelling results for the surface

A. Coustenis, E. Lellouch (DESPA, Paris-Meudon Observatory, France), B. Schmitt (LGGE, Grenoble, France), P. Rannou, M. Cabane (Serv. d'A\'eronomie, Univ. Paris 6, France), C. P. McKay (NASA/AMES), J.-P. Maillard (Inst. Astroph. Paris)

Observations of Titan in the near infrared have been continuously exercised from the ground since over a decade now, bringing new, exciting information on the nature of the satellite's surface. In combination with images from the HST and the adaptive optics systems (ADONIS, PUEO), the data help acquire constraints for modelling the possibilities of a ground which has avoided direct detection, even by space missions.

High resolution spectra of Titan in the near infrared (0.9-2.5 \mum, where five atmospheric methane windows appear) were acquired since 1991 by use of the the Fourier Transform Spectrometer (FTS) at the CFHT. The data obtained yield information on the Titan's geometric and surface albedo, on the lightcurves, on the ground topography and on the possible constituents on the surface (Coustenis et al. 1995; 1998).

In a recent work, we have used the radiative transfer code based on McKay et al. (1989), upgraded to include an aerosol distribution of fractal particles instead of spherical (Rannou et al., 1995). This code has allowed us to infer the surface albedo at different longitudes on Titan's disk. We have then modelled the surface albedo using combinations of various surface components, such as water ice, tholin material, methane ice, etc. The comparisons are based on laboratory data produced by Schmitt et al. (1998). We will present our findings which bring constraints on the composition of the satellite's surface (Coustenis et al., 1998)

{\bf References} COUSTENIS, A., {\em et al.} 1995. {\em Icarus} {\bf 118}, 87-104. COUSTENIS, A., {\em et al.} 1998. To be submitted for publication. \\ McKAY, C. P., {\em et al.} 1989. {\em Icarus} {\bf 80}, 23-53. \\ RANNOU, P., {\em et al.} 1995. {\em Icarus} {\bf 118}, 355-372. \\ SCHMITT, B., {\em et al.} 1998. In {\em "Solar System Ices"}, B. Schmitt et al., Eds, Kluwer Acad. Publ, A.S.S.L., {\bf 227}, 199-240.