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S. J. Kim (Department of Astronomy and Space Science, Kyung Hee University, Korea), T. Geballe (Gemini Observatory)
The recent spectroscopic detection of 3-micron fluorescent emission of CH4 from Titan (Kim et al. 2000) opened a new way of probing the high altitude atmosphere of Titan via ground-based observations. The sharp CH4 emission lines can be seen through the 3-micron atmospheric window in between strong telluric CH4 absorption lines. The conclusion by Kim et al. (2000) that the CH4 emission mainly arises at 400 - 750 km altitudes has been verified by VIMS/Cassini imaging conducted during the close encounter with Titan. Analysis of the ro-vibrational bands of HCN and CH4 also allows temperatures in the high-altitude atmosphere to be derived (Geballe, et al. 2003; Kim et al. 2005). The 3-micon fluorescence is found to originate at microbar pressure levels, where non-LTE processes dominate. This successful investigation indicates that 3-micron ground-based spectroscopy is still a useful and a low-cost way to probe the atmosphere of Titan in the current Cassini era. The 3-micron spectrum of Titan also reveals absorption lines of CH3D. We will present the high-resolution (R ~ 25,000) spectrum of Titan obtained with NIRSPEC at Keck II, on which some of the above discoveries are based, and will discuss non-LTE radiative processes in Titan's upper atmosphere and reflection of solar radiation by clouds/haze. We will also present many unidentified absorption lines in the high-resolution spectrum, and discuss possible candidates for these lines.
References
Kim, S.J., Geballe, T.R., and Noll, K. 2000. Icarus, 147, 588. Geballe, T.R., Kim, S.J., Noll, K.S., and Griffith, C.A. 2003. Ap. J. 583. L39 Kim, S.J., Geballe, T.R., Noll, K.S., and Courtin, R. 2005. Icarus, 173, 522-532.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.