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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[45.13] Trapping of the Noble Gases Ar, Kr and Xe in aerosols formed by C2H2 + HCN photolysis - implications to Titan

R. Jacovi, D. Laufer, V. Dimitrov, A. Bar-Nun (Department of Geophysics and Planetary Sciences, Tel-Aviv University,)

Titan's atmosphere was found by the Cassini (INMS) flyby at ~1200km above Titan's surface to be devoid of Kr and Xe, with only traces of 40Ar and no other Ar isotopes. During our studies of the polymerization of C2H2:HCN:N2 = 10:1:70 mixtures by UV photolysis and the subsequent formation of aerosols, as observed on Titan, we found that the aerosols trap the noble gases. From the rate of formation and sedimentation of the aerosols, together with their trapping efficiencies for Ar, Kr and Xe, it can be shown that Kr, Xe and 36Ar, 38Ar were entirely deposited on Titan's surface, with traces of 40Ar being constantly evolving from a radiogenic source. Following the non-detection of lightning discharges and thunderclaps in Titan's atmosphere by the Huygens HASI experiment, it seems that solar UV irradiation is the major energy source driving Titan's atmospheric chemistry. UV irradiation of a C2H2:HCN = 10:1 mixture results in an aerosol composition of C:H:N = 1:1:0.07. The nitrogen content is much smaller than that found in experiments using electrical discharges. A C:H ratio of ~1 in the aerosols might hint on their composition, namely, polyvinyls and some aromatics.

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Bulletin of the American Astronomical Society, 37 #3
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