37th DPS Meeting, 4-9 September 2005
Session 45 Titan's Atmosphere
Poster, Wednesday, September 7, 2005, 6:00-7:15pm, Music Recital Room

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[45.23] Measuring Titan's mesospheric temperatures by infrared spectroscopy

P. Penteado, C. Griffith (Lunar and Planetary Laboratory), T. Greathouse (Lunar and Planetary Institute), H. Roe (California Institute of Technology, Div. of Geologycal and Planetary Sciences), R. Yelle (Lunar and Planetary Laboratory)

Titan's temperature profile is an indicator of the atmospheric energy transport, by radiation, convection and conduction. From the surface up to ~250 km altitude, the temperature profile was measured by the Voyager 1 radio occultations and infrared spectra. In the troposphere, heating by the surface and low atmosphere by solar radiation absorption and cooling by emission to space are the dominant processes that establish the temperature profile, which decreases from ~94 K at the surface, to ~70 K at 200 km. Between 200 and 350 km, the atmosphere radiative absorption and emission balance, and the temperature is approximately constante. At 250-500 km altitudes, observations of stellar occultations reveal oscillations between 170 and 150 K. Atmospheric models predict the existence of a mesosphere, in the region 350-550 km, with the temperature decreasing from ethane and other hydrocarbons' emissions. In this work we analyze emission lines of methane's \nu4 band (8.1 \mum, 1230 cm-1) with high resolution spectra. The line profiles of different intensities allow us to determine the vertical temperature profile for the region 100-600 km, which was not possible with previously available data. We present the first infrared observation that can measure independently the temperatures for the regions 100-200 km, 200-400 km, and 400-600 km. These measurements show the existence of a mesosphere, with a temperature drop of at least 15 K from 380+50-100 km altitude.

Paulo Penteado is sponsored by the NASA Planetary Astronomy Program and the Brazilian Government through CAPES.

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

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