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E. Karkoschka, M. Tomasko, L. Doose (Univ. of Arizona), M. Lemmon (Texas A&M Univ.)
The upward and downward looking visible spectrometers on the Descent Imager / Spectral Radiometer recorded spectra between 480 and 970 nm wavelength at 5 nm spectral resolution. We received 246 upward and 854 downward spectra taken between 0 and 140 km altitude. The spin of the Huygens probe provided the full azimuthal coverage. The upward looking spectra essentially recorded the downward flux, while the downward looking spectra had 20 spatial resolution elements.
This data set gives good constraints on the optical depth and properties of aerosols in Titan's atmosphere. The vertical distribution of aerosols, in particular, is far better constrained than from any other observation taken from outside Titan's atmosphere.
Our modeling approach with a doubling and adding code started with distributions and properties of aerosols from previous studies. We soon realized that we had to lower the lower boundary of the aerosol layer from the previously considered 70 km all the way to the ground in order to explain the new observations. The upper boundary is near 150 km as estimated before, aside from hazes of very low optical depth present at much higher altitudes. The observed variation of intensity with phase angle and the variation with wavelength yielded tight constraints on the size and fractal nature of the aerosols.
We also recorded the increase of methane absorption looking at the sun as Huygens descended to the surface. This may be the first observation of the transmission spectrum of methane at the temperatures and pressures of Titan, similar to conditions of the stratospheres of the Jovian planets, but very different from laboratory conditions. Our results may resolve previous uncertainties in studies of methane absorptions in the Jovian planets.
This work is supported by JPL contract 961160.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.