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T. A. Livengood, J. J. Goldstein (Challenger Ctr.), T. Hewagama, K. E. Fast (U of MD), Th. Kostiuk, F. Espenak, D. Buhl (NASA's GSFC)
We have made an improved determination of the ethane (C2H6) mole fraction in Titan's stratosphere using data from the Goddard Infrared Heterodyne Spectrometer (IRHS) at the NASA Infrared Telescope Facility. Ethane is an important constituent in the hydrocarbon photochemical cycle of outer solar system atmospheres. Ethane spectral lines were observed in emission from Titan in August 1993, October 1995, and September 1996, at a spectral resolution of \lambda / \Delta \lambda \approx 106, at 11.7--11.9~\mum wavelength. The measured ethane mole fraction is (8.7 ±2.3) \times 10-6~cm-3, using the standard thermal profile of Yelle et al. [in Huygens: Science, Payload and Mission, J.-P. Lebreton, Ed. (European Space Agency SP-1177, 1997) pp. 243-256)]. The precision in this new determination is considerably higher than in previously reported measurements. Fully resolved emission lineshapes and lines of different lower-state energy in the heterodyne spectra provide the ability to partially resolve the ambiguity between temperature and abundance in infrared spectra. We will discuss the influence of the thermal profile upon the retrieved ethane concentration and constraints upon the thermal profile obtainable from these measurements.
This work is supported by the NASA Planetary Astronomy Program.
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