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Published January 30, 1986 | public
Journal Article

D to H ratio and the origin and evolution of Titan's atmosphere

Abstract

A value of 1.7 × 10^(−3) has been reported for the ratio of CH_3D to CH_4 in the stratosphere of the saturnian moon Titan. A lower value of 6 × 10^(−4) for this ratio in the deeper part of Titan's atmosphere was reported by de Bergh et al. For comparison we note that the CH_3D to CH_4 ratio on Saturn and Jupiter is 8.7 × 10^(−5) and 6.7 × 10^(−5), respectively (see Table 1). We estimate the uncertainties in all these observations and data reduction to be about a factor of 2. Despite these uncertainties it appears that Titan's atmosphere is enriched in deuterium by a factor of ≥3 relative to Jupiter and Saturn. Potential causative factors examined here for this enrichment are condensation to form tropospheric methane clouds, fractionation occurring over a hypothetical CH_4–C_2H_6 ocean and between the ocean and the clathrate crust beneath, fractionation which occurred during the formation of Titan and fractionation occurring as a result of the evolution of Titan's atmosphere. We conclude that the greater part of the observed fractionation is probably derived from the formation of Titan and the subsequent evolution of Titan's atmosphere driven by photochemistry.

Additional Information

© 1986 Nature Publishing Group. Received 20 May; accepted 14 October 1985. We thank Mark Allen, Larry Nyquist, AI Laufer, Ray Reynolds and Dave Stevenson for useful discussions and Catherine de Bergh, Barry Lutz, Tobias Owen, Sam Epstein and Jongmann Yang for communication of their results before publication. This research was supported by NASA grants NAGW-254 and NSG 7376 to the California Institute of Technology. Contribution no. 4164 of the Division of Geological and Planetary Sciences, California Institute of Technology.

Additional details

Created:
August 22, 2023
Modified:
October 17, 2023