Evidence for water vapor in Titan's atmosphere from ISO/SWS data ?

Abstract

The infrared spectrum of Titan around 40µ mw as recorded in the grating mode of the Short Wavelength Spectrom- eter (SWS) of ISO, with a resolving power of about 1900. Two emission features appear at 43.9 and 39.4µm, where pure rota- tional water lines are expected. Line strengths are about 8 times the 1� statistical noise level. The H2O vertical profile for wa- ter suggested by the photochemical model of Lara et al. (1996), rescaled by a factor of about 0.4 +0.3 0.2, is compatible with the data. The associated water mole fraction is about 8 +6 4 × 10 9 at an altitude of 400 km (column density of 2.6 +1.9 1.6 ×10 14 mol cm 2 above the surface). The inferred water influx at 700 km in Titan's atmosphere is in the range (0.8-2.8) ×10 6 mol cm 2 s 1 .