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Photochemistry of the atmosphere of Titan: comparison between model and observations

Yung, Yuk L. and Allen, Mark and Pinto, Joseph P. (1984) Photochemistry of the atmosphere of Titan: comparison between model and observations. Astrophysical Journal Supplement Series, 55 (3). pp. 465-506. ISSN 0067-0049. doi:10.1086/190963.

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The photochemistry of simple molecules containing carbon, hydrogen, nitrogen, and oxygen atoms in the atmosphere of Titan has been investigated using updated chemical schemes and our own estimates of a number of key rate coefficients. Proper exospheric boundary conditions, vertical transport, and condensation processes at the tropopause have been incorporated into the model. It is argued that the composition, climatology, and evolution of Titan's atmosphere are controlled by five major processes: (a) photolysis and photosensitized dissociation of CH_4 ; (b) conversion of H to H_2 and escape of hydrogen; (c) synthesis of higher hydrocarbons; (d) coupling between nitrogen and hydrocarbons; (e) coupling between oxygen and hydrocarbons. Starting with N_2, CH_4, and H_20, and invoking interactions with ultraviolet sunlight, energetic electrons, and cosmic rays, the model satisfactorily accounts for the concentrations of minor species observed by the Voyager IRIS and UVS instruments. Photochemistry is responsible for converting the simpler atmospheric species into more complex organic compounds, which are subsequently condensed at the tropopause and deposited on the surface. Titan might have lost 5.6 × 10^4 , 1.8 × 10^3, and 4.0 g cm^-2 , or the equivalent of 8,0.25, and 5 × 10^-4 bars of CH_4, N_2 , and CO, respectively, over geologic time. Implications of abiotic organic synthesis on Titan for the origin of life on Earth are briefly discussed.

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Yung, Yuk L.0000-0002-4263-2562
Additional Information:© 1984 The American Astronomical Society. Received 1983 August 29; accepted 1984 January 6. We thank A. H. Laufer, M. R. Berman, M. C. Lin, H. Okabe, A. M. Renlund, R. Hanel, W. Maguire, R. E. Samuelson, D. M. Hunten, D. E. Shemansky, D. F. Strobel, V. McKoy, T. Owen, and D. O. Muhleman for communication of results prior to publication, and W. B. DeMore, W. T. Huntress, Jr., S. Trajmar, M. B. McElroy, R. M. Goody, C. Sagan, R. K. Sparks, L. C. Lee, and K. Rages for helpful discussions. This research was supported by NASA grants NAGW-254 and NSG 7376 to the California Institute of Technology.
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Subject Keywords:planets: abundances; planets: atmospheres; planets: satellites; planets: Saturn
Issue or Number:3
Record Number:CaltechAUTHORS:20140909-090508298
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:49480
Deposited By: Jason Perez
Deposited On:10 Sep 2014 17:53
Last Modified:10 Nov 2021 18:44

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