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EPSC Abstracts Vol. 6, EPSC-DPS2011-29-1, 2011 EPSC-DPS Joint Meeting 2011 c Author(s) 2011 Titan's Mid-Atmospheric Photochemistry: the chemical composition of the Aerosols and Their Rate of Accumulation on the Surface Akiva Bar-Nun, Diana Laufer, Ronen Jacovi, and Vasili Dimitrov Department of Geophysics and Planetary Sciences, Tel-Aviv University, Tel-Aviv, 69978, Israel, akivab@post.tau.ac.il/Fax: 972-3-6409282 Abstract As found by the Cassini GC-MS, a plethora of organics are produced in Titan’s upper atmosphere by short UV, cosmic rays and Saturn’s magnetospheric particles. These energy sources convert the CH4, and N2 into mainly C2H2, C2H4, HCN and HC3N, which reach a lower altitude at the observed mixing ratios of 3x10-6, 10-7-10-8, 3x10-7 and 10-9-10-10, respectively. Reaching down to midaltitudes, these unsaturated compounds are activated by UV irradiation and form a plethora of hydrocarbons and nitriles, which produced the thick layer of aerosols in Titan’s atmosphere. mere deposition of 10-6 cm per year, easily washable by the methane and ethane rains. These aerosols also trap the noble gases Ar, Kr and Xe, which are highly depleted in Titan’s atmosphere [2]. 3. Figures 1. Experimental Results Photolysis of C2H2, C2H4 and HCN in the presence of CH4 by a low pressure Mercury lamp, emitting 38 mW cm-2 at 2537 Å and about ten times less at 1849 Å, polymerize these unsaturated compounds to form, by stepwise addition of C2 and ring closure, polyaromatic hydrocarbons (PAHs). When rings are not closed, polyvinyls, which cross-link form an insoluble 3-dimentional matrix [1]. The main constituents in the gas phase (Figure 1a) is benzene, diacetylene, methane and ethane and up to C8H8styrene. In the solid phase (Figure 1b) the main constituents are biphenyl, naphthalene and phenyl acetylene, up to the condensed 5-ring pyrene. Figure 1a: Gas Phase Products 2. Aerosols’ Formation Rate The rate of aerosol formation (figure 1c) leads to a ~ 42 m thick layer during Titan’s life time, 4.6 by. A Figure 1b: Solid Phase Products Acknowledgements This research was supported by the Israel National Science Foundation, grant 66/03. Special thanks to Zipi Rosen for computer assistance. References Figure 1c: Electron Microscopy of the aerosols 4. Summary and Conclusions These measurements are important for better understanding the composition of atmospheric chemistry and Titan’s aerosols as well as the composition of the recently discovered lakes on Titan. Another matter could be the composition of water-less Exo-planets. [1] Jacovi R., Laufer D., Dimitrov V., Bar-Nun A. Chemical composition of simulated Titan’s midatmospheric aerosols. J. Geophys. Res., 115, E07006, doi:10.1029/2010JE003585, 2010. [2] Jacovi R. and Bar-Nun A. Removal of Titan’s noble gases by their trapping in its haze. Icarus, 196, 302-304, 2008.