Titan's gaseous composition has been inferred in Titan's stratosphere from data recorded by the Composite Infrared Spectrometer (CIRS) aboard the Cassini spacecraft (Flasar et al., 2005; Teanby et al., 2006, 2007a,b; Coustenis et al., 2007a,b; Vinatier et al., 2007). We will present an update from all data available from the Titan flybys spanning three years since SOI. The spectra characterize various regions on Titan from 85°S to 80°N with a variety of emission angles. We study the emission observed in the mid-infrared CIRS detector arrays (covering roughly the 600-1500 cm-1 spectral range with apodized resolutions of 2.54 or 0.53 cm-1). The composite spectrum shows several molecular signatures: hydrocarbons, nitriles and CO2. A firm detection of benzene (C6H6) is provided by CIRS at 674 cm-1 and allows for the study of its latitudinal variation (Coustenis et al., 2007a,b). C2HD was detected from its emission at 678 cm-1 (Coustenis et al., 2007c, in preparation). We have used temperature profiles retrieved from the inversion of the emission observed in the methane ν4 band at 1304 cm-1 (Achterberg et al., 2007) and a radiative transfer code to infer the abundances of the trace constituents and some of their isotopes in Titan's stratosphere (Nixon et al., 2007; Coustenis et al., 2007c, in preparation). No longitudinal variations were found for the gases. Information is retrieved on the meridional variations of the trace constituents and tied to predictions by dynamical-photochemical models. Molecules showing a significant enhancement at northern latitudes are the nitriles (HC3N, HCN) and the complex hydrocarbons (C4H2, C3H4, C6H6). The D/H ratio on Titan was determined from the CH3D band at 8.6 micron and found to be about 1.3 ±0.2 10-4 (Coustenis et al., 2007a,b; Bézard et al., 2007). D/H is also determined in acetylene (about 1.8±0.5 10-4).
AAS/Division for Planetary Sciences Meeting Abstracts #39
- Pub Date:
- October 2007