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Published May 2005 | public
Journal Article

Isotopic fractionation of methane in the martian atmosphere


The existence of methane in the martian atmosphere may be an indicator of subsurface life. Biological processes are known to fractionate the common isotopologues of methane, and hence measuring these isotopic ratios may yield constraints on the nature of the methane source. Any measurement of the isotopic ratios of atmospheric methane must consider the additional fractionation due to photochemistry in order to quantify the isotopic ratios of the source. Using a one-dimensional photochemical model, we find that photochemistry has a small (4.5‰) contribution to δ^(13)C(CH_4) but has a large (114‰) contribution to δD(CH_4). Confirmation of these fractionation values will require additional laboratory data on key model inputs, particularly the ultraviolet absorption cross sections of ^(13)CH_4 and kinetic rate coefficients for the reactions of ^(13)CH_4 and CH_3D with OH and O(^1D) at pressures and temperatures relevant to the martian atmosphere.

Additional Information

© 2004 Elsevier Inc. Received 17 August 2004; revised 26 October 2004. Available online 21 January 2005. We thank M. Gerstell for a critical reading of the manuscript. This work was supported in part by an NSF grant and the NASA Astrobiology Institute at JPL.

Additional details

August 22, 2023
October 17, 2023