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Titan at 3 microns: Newly identified spectral features and an improved analysis of haze opacity |
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| Authors: | Haingja Seo Joo Hyeon Kim Régis Courtin |
| Institution: | a Department of Astronomy and Space Science, Kyunghee University, Yongin 446-701, Republic of Korea b Gemini Observatory, 670 N. A'ohoku Place, Hilo, HI 96720, USA c LESIA, CNRS/Observatoire de Paris, 5 place Jules Janssen, 92195 Meudon, France d Jet Propulsion Laboratory, California Institute of Technology, MS 183-601, 4800 Oak Grove Dr., Pasadena, CA 91109, USA |
| Abstract: | We have reanalyzed the high-resolution spectrum of Titan between 2.87 and 3.12 μm observed with NIRSPEC/Keck II on 2001 Nov. 21 in southern summer, using updated CH3D and C2H6 line-by-line models. From new synthetic spectra, we identify all but a few of the previously unidentified significant absorption spectral features in this wavelength range as due to these two species, both of which had been previously detected by Voyager and ground-based observations at other wavelengths. We also derive opacities and reflectivities of haze particles as functions of altitude for the 2.87-2.92 μm wavelength range, where Titan's atmosphere is partially transparent down to the surface. The extinction per unit altitude is observed to increase from 100 km (∼8 mbar) toward lower altitude. The derived total optical depth is approximately 1.1 for the 2.87-2.92 μm range. At wavelengths increasing beyond 2.92 μm the haze layers become much more optically thick, and the surface is rapidly hidden from view. These conclusions apply to equatorial and southern-temperate regions on Titan, excluding polar regions. We also find it unlikely that there is a large enhancement of the tropospheric CH4 mole fraction over the value reported from analysis of the Huygens/GCMS observations. |
| Keywords: | Titan Atmospheres composition Spectroscopy Infrared observations Saturn satellites |
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