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Published August 1, 2010 | Published
Journal Article Open

Cosmic-ray-mediated Formation of Benzene on the Surface of Saturn's Moon Titan


The aromatic benzene molecule (C_6H_6)—a central building block of polycyclic aromatic hydrocarbon molecules—is of crucial importance for the understanding of the organic chemistry of Saturn's largest moon, Titan. Here, we show via laboratory experiments and electronic structure calculations that the benzene molecule can be formed on Titan's surface in situ via non-equilibrium chemistry by cosmic-ray processing of low-temperature acetylene (C_2H_2) ices. The actual yield of benzene depends strongly on the surface coverage. We suggest that the cosmic-ray-mediated chemistry on Titan's surface could be the dominant source of benzene, i.e., a factor of at least two orders of magnitude higher compared to previously modeled precipitation rates, in those regions of the surface which have a high surface coverage of acetylene.

Additional Information

© 2010 The American Astronomical Society. Received 2009 November 11; accepted 2010 April 11; published 2010 July 14. The experimental work was supported by the Chemistry Division of the US National Science Foundation within the framework of the Collaborative Research in Chemistry (CRC) Program (NSF-CRC CHE-0627854; LZ, WZ, RIK, AMM).We are very much indebted to Matthew R. Hammond and Richard N. Zare, Department of Chemistry, Stanford University, Stanford, CA, for the LDI measurements. One of us (Y.L.Y.) thanks T. Orlando (Georgia Tech) for valuable discussion. Y.L.Y. is supported by NASA grant NASA5-13296 to the California Institute of Technology. M.C.L. is supported by NSC grant 98- 2111-M-001-014-MY3 to Academia Sinica. We thank Tobias Owen (Institute for Astronomy, University of Hawaii) and Roger Yelle (LPI, Arizona) for stimulating discussions and valuable comments on this manuscript. Special thanks are due to Keran O'Brien (Northern Arizona University) for sharing details on the calculations on the cosmic-ray exposure on Titan's surface.

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