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Abstract: Analysis of the Cassini Ultraviolet Imaging Spectrometer (UVIS) stellar andsolar occultations at Titan to date include 12 species: N$ {2}$ (nitrogen),CH$ {4}$ (methane), C$ {2}$H$ {2}$ (acetylene), C$ {2}$H$ {4}$ (ethylene),C$ {2}$H$ {6}$ (ethane), C$ {4}$H$ {2}$ (diacetylene), C$ {6}$H$ {6}$(benzene), C$ {6}$N$ {2}$ (dicyanodiacetylene), C$ {2}$N$ {2}$ (cyanogen), HCN(hydrogen cyanide), HC$ {3}$N (cyanoacetylene), and aerosols distinguished by astructureless continuum extinction (absorption plus scattering) of photons inthe EUV. The introduction of aerosol particles, retaining the same refractiveindex properties as tholin with radius $\sim$125 \AA and using Mie theory,provides a satisfactory fit to the spectra. The derived vertical profile ofaerosol density shows distinct structure, implying a reactive generationprocess reaching altitudes more than 1000 km above the surface. A photochemicalmodel presented here provides a reference basis for examining the chemical andphysical processes leading to the distinctive atmospheric opacity at Titan. Wefind that dicyanodiacetylene is condensable at $\sim$650 km, where theatmospheric temperature minimum is located. This species is the simplestmolecule identified to be condensable. Observations are needed to confirm theexistence and production rates of dicyanodiacetylene.



Author: Mao-Chang Liang, Yuk L. Yung, Donald E. Shemansky

Source: https://arxiv.org/







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