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C.M. Anderson (New Mexico State University), E.F. Young (Southwest Research Institute), N.J. Chanover (New Mexico State University), C.P. McKay (NASA/Ames Research Center)
We report high spatial resolution (320 km at the sub-Earth point) and spectral resolution (1 nm) visible/near-infrared observations of Titan taken at Ls=240 in November 2000. These data were obtained with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope through program GO-8580. We utilize 122 wavelengths that span Titan's 0.6 to 1 micron spectral range to address the tropospheric methane abundance, degree of methane supersaturation and haze concentration in Titan's lower stratosphere and troposphere. The contribution functions in the 0.6 to 1 micron range peak at altitudes from 100 km down to a few km above the surface. The 0.619 micron methane feature is of particular interest since it is highly sensitive to the amount of methane and haze, and previous investigators (Tomasko et al. 1997, ESA SP-1177, 345-358; Rannou et al. 2003, Plan. Space Sci. 51, 963-976) have had difficulty matching Titan's modeled and observed geometric albedo spectrum when they include this wavelength. To interpret these STIS data, we employ a 1D radiative transfer fractal particle model with a Bayesian parameter estimation algorithm that adjusts Titan's haze opacity below 100 km, the methane mole fraction below 34 km, the surface albedo, and the haze single scattering albedo.
Retrieving the tropospheric methane and lower atmosphere haze profiles is crucial for understanding the interactions between the haze and methane in the atmosphere and on the surface. Results of this work may help to constrain Titan's haze opacity in dynamical models, and examine the spatially varying degree of methane supersaturation in conjunction with areas of known cloud formation. The correlation of our results with the Huygens Probe data showing reduced haze in the lower atmosphere will be discussed.
Funding for this work was provided by the NASA Graduate Student Researchers Program and grant number AST-0335635 from the National Science Foundation.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.