HR: 16:50h
AN: P44A-03    [Abstracts]
TI: The atmospheric structure of Titan from Voyager to Cassini
AU: * Coustenis, A
EM: athena.coustenis@obspm.fr
AF: Athena Coustenis, LESIA (Bat. 18) Observatoire de Meudon 5, place Jules Janssen, Meudon, 92195, France
AB: Titan's stratosphere has been studied in the past from the Earth and also from space with Voyager, ISO (Coustenis et al., 1998; 2003) and more recently Cassini observations. In particular, spectra recorded by the Composite Infrared Spectrometer (CIRS) aboard the Cassini spacecraft became available during the Titan flybys spanning two years now since SOI (Flasar et al., 2005; Teanby et al., 2006, Vinatier et al., 2006; Nixon et al., 2006; Coustenis et al., 2007). The spectra characterize various regions on Titan from 85°S to 80°N with a variety of emission angles. We have studied the emission observed in the CIRS detector arrays (covering the 10-1500 cm^-1 spectral range with apodized resolutions of 2.54 or 0.53 cm^-1). We have used temperature profiles retrieved from the inversion of the emission observed in the methane _4 band at 1304 cm^-1 and a line-by-line radiative transfer code to infer the abundances of the trace constituents and some of their isotopes in Titan's stratosphere (Coustenis et al., 2007). The composite spectra show several signatures of previously identified molecules: hydrocarbons, nitriles, H₂O and CO₂. Besides these well-known trace species, a firm detection of benzene (C₆H₆) is provided by CIRS at 674 cm^-1 and allows for the study of its latitudinal variations. No longitudinal variations were found for any of the gases. Information is retrieved on the meridional variations of the trace constituents and tied to predictions by dynamical-photochemical models (Hourdin et al., 2004; Lavvas et al., 2007). Molecules showing a significant enhancement at northern latitudes are the nitriles (HC₃N, HCN) and the complex hydrocarbons (C₄H₂, C₃H₄). The D/H ratio on Titan was also determined from the CH₃D band at 8.6 micron and found to be about 1.2 ± 0.2 10^-4. We have also identified the presence of C₂HD at 678 cm^-1 (Coustenis et al., 2006). Constraints are also set on the vertical distribution of C₂H₂. We will describe the most relevant results from ground or space regarding Titan's atmospheric structure. References : Coustenis et al., 1998, A&A 336, L85; Coustenis et al., 2003, Icarus 161, 383; Coustenis et al., 2006, BAAS 38; Coustenis et al., 2007, Icarus, in press; Flasar et al., 2005, Science 308, 975 ; Hourdin et al., 2004, J. Geophys. Res. 109, E1205; Nixon et al., 2006, BAAS 38; Lavvas et al., 2007, Plan. Space Sci., submitted; Teanby et al., 2006, Icarus 181, 243; Vinatier et al., 2006, Icarus, in press.
DE: 5405 Atmospheres (0343, 1060)
DE: 5410 Composition (1060, 3672)
DE: 5470 Surface materials and properties
SC: Planetary Sciences [P]
MN: 2007 Joint Assembly