nai

Project Progress

We published the work on longer wavelength photochemistry of condensed organic ices in Titan’s lower atmosphere in Nature Communications this year, based on our past years work, and continued more studies on the photochemistry of acetylene trapped in dicyanoacetylene as well as acetylene trapped cyanodiacetylene. The laboratory work in 2013 was mainly focused on surface photochemistry simulations of Titan’s condensed aerosols on the surface using laboratory analogs (tholins) on which abundant molecules such as acetylene were condensed in order to simulate surface solid photochemistry involving most abundant unsaturated molecule (acetylene) on Titan. Our results in longer wavelength photochemistry of C₄N₂ ice prompted reexamination of UV-VIS light reaching Titan’s surface, measured by Huygens probe, showing that the flux of >350 nm light reaching Titan’s surface is not insignificant. Based on these ideas, we focused our studies more towards understanding longer wavelength photochemical activity of Titan’s surface organic simulants.

We started a collaborative work this year with Dr. Nathalie Carrasco and her student Benjamin Fleury, who brought discharge tholin samples with various degree of methane in N₂ atmosphere, simulating the Titan’s atmospheric aerosols. These materials were prepared on a sapphire window, which could be directly mounted on a cryogenic system and cooled to desired cryogenic temperatures under vacuum. To begin with, we tested pure acetylene ice at 50 K by laser irradiation at 355 nm. Depletion over a long period of time (several hours) was negligible. Then we simulated accretion of acetylene (Titan’s abundant volatile) on aerosol analogs (tholins prepared under various conditions). We found that when deposited over tholins, acetylene depletion upon laser irradiation is more significant.

Further systematic studies are underway, using various laboratory-generated Titan’s aerosol analogs (which also represent Titan’s surface organic solids), now produced by Dr. Mark Smith’s lab (University of Houston) as well. We are presently analyzing the data for several publications. Our results indicate that while VUV irradiation resulted in extensive photochemical processing, longer wavelength photochemistry is slow, but not negligible in Titan’s lower atmosphere and on the solid surface. These new photochemical channels could contribute to the formation of complex organics as well as prebiotic molecules in regions of water abundance on Titan.