RECENT APPLICATIONS AND FUTURE PROSPECTS OF METHANE SPECTROSCOPY TO THE ATMOSPHERE OF TITAN

Abstract

The advent of the Cassini-Huygens mission studying Saturn's system and its largest moon Titan, has led to a renewed interest in reliable models of the absorption spectrum of methane. CH$_4$ is the main absorber in Titan's thick atmosphere. Although the models developed in the Dijon group still do not allow sufficently reliable simulations above 5000 cm$^{-1}$ to reproduce all the recent data (such as Huygens/DISR spectra, for instance), the methane coefficients in the 0--4800 cm$^{-1}$ region have contributed to a better understanding of various ground- and spaced-based data : ISO high-resolution data in the 3 $\mu$m region} {\em Icarus\/} {\bf 180}, 176--185 (2006).}, near-infrared VLT data} {\em Planet. Space Sci.\/} {\bf 54}, 1225--1246 (2006).} and 2 $\mu$m VLT data of the Huygens probe landing site} {\em J. Geophys. Res. Planets\/} {\bf 112}, E02S92 (2007).}. These coefficients have also contributed to the discovery of a polar ethane cloud on Titan} {\em Science\/} {\bf 313}, 1620--1622 (2006).}. Models of CH$_4$ hot bands by the Dijon group are also of primary importance for fluorescence calculations observed at 3.3 $\mu$m with Cassini/VIMS}, Astron. Astrophys. {\bf 446}, 707--716 (2006).}. After a short review of these works, future prospects for line-by-line analyses of CH$_4$ spectra for planetary applications will also be discussed and compared to other approaches, such as the so-called band models or purely experimental approaches.