TITAN ATMOSPHERIC STRUCTURE FROM VOYAGER-2 INFRARED-SPECTRA

Voyager 2 flew by Titan 9 months after Voyager 1 at a distance from its centre 100 times greater at closest approach (27 August 1981). A total of 115 infrared spectra are analysed here (taken mainly between 15-degrees-S and 60-degrees-N of latitude at emission angles < 50-degrees). The projected field of view of IRIS (the infrared spectrometer onboard) on Titan's disc is at best 60-degrees, thus allowing for only two locally independent spectral selections. Our atmospheric model is applied on spectral averages covering the 200-1400 cm-1 range (resolution = 4.3 cm-1). Molecules such as C2H2, C2H6, C3H4, C4H2, CH4, HCN and CO2 were clearly identified in emission with significant signal-to-noise ratios. Spectral features on the 3sigma level appear at frequencies where C3H8 and C2H4 have signatures. No significant temporal variations within the 9 months were detected. Latitudinal variations exist both in temperature and composition. Our findings confirm previous analyses of Voyager 1 data and validate the associated atmospheric model.