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[39.01] Water Influx at Titan

R. E. Samuelson, G. L. Bjoraker (NASA/GSFC), A. Coustenis, E. Lellouch (DESPA Paris-Meudon Observatory, France), A. Salama (ISO Sci. Oper. Center, Madrid, Spain), D. P. Hamilton (U. of Maryland)

Water vapor lines at 227.8 and 254.0 cm^-1 were discovered in Titan's stratosphere from observations taken with the ISO Short Wavelength Spectrometer (SWS) in the grating mode. Line strengths are ~ 8 times the 1\sigma statistical noise level, with a resolving power ~ 2000. A recent photochemical model [1] predicts correct H₂O/CO₂ line strength ratios, provided the actual H₂O abundance is 0.4 that of the model. Using this scale factor of 0.4, we infer a water influx of 0.8 - 2.8 \times 10⁶ mol cm^-2 s^-1 at Titan, referred to an altitude of 700 km. This is comparable to the H₂O influx of 0.3 - 5.0 \times 10⁶ mol cm^-2 s^-1 found at Saturn [2]. We discuss ice dust production and transport mechanisms in the Saturn system that might give rise to such values.

{\bf References:} [1] LARA, L. M., {\em et al.} (1996), {\em J. Geophys. Res. - Planets} {\bf 101}, 23261 - 23283. [2] FEUCHTGRUBER, H., {\em et al.} (1997), {\em Nature} {\bf 389}, 159 - 162.