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[45.19] Remote measurement of infrared emission by ethane in Titan's stratosphere at the Huygens entry epoch

T. A. Livengood (USRA NCSEFSE), Th. Kostiuk (NASA GSFC), G. Sonnabend (NAS/NRC at NASA GSFC), J. N. Annen, K. E. Fast (NASA GSFC), A. Tokunaga (U of HI), K. Murakawa (MPIfR, Bonn), T. Hewagama (U of MD), F. Schmülling, R. Schieder (U Köln)

The equatorial region of Titan was observed on 14 and 15 January 2005 UT, during and following the entry of the Huygens Probe, using the Goddard Space Flight Center Heterodyne Instrument for Planetary Winds and Composition (HIPWAC) on the Nasmyth focus of the Subaru 8.2~m telescope of the National Astronomical Observatory of Japan. The observed infrared spectral features are formed by thermal emission of ethane gas in the stratosphere and lower mesosphere. Three regions were observed, at each of the East and the West limb and at disc center. The observed distribution of line strengths and lineshapes differs from observations obtained the previous year from Subaru and also differs from observations obtained at the NASA Infrared Telescope Facility in prior years, suggesting temporal variability either in the thermal profile or in the vertical distribution of ethane. The structure of Titan's upper stratosphere/lower mesosphere thus may be different at the beginning of the Cassini tour than during the preceding decade. Three radio-frequency (RF) spectral analysis systems were used to resolve the double sideband infrared spectrum at 11.74 \micron wavelength to a resolving power of \lambda / \Delta\lambda = 10⁶, 5\times 10⁶, and 25\times 10⁶, respectively, providing confirmation of results obtained with any one RF system. IR heterodyne spectral resolution provides insight into atmospheric phenomena not observable by lower-resolution spectroscopic techniques.

This work is supported by the NASA Planetary Astronomy Program.

The author(s) of this abstract have provided an email address for comments about the abstract: tlivengood@usra.edu

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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.