A Sensitive Search for Methane on Mars

CH₄ and its oxidation products (H₂CO, CH₃OH, C₂H₆) on Mars have received both observational (1) and theoretical attention (2, 3), but have not been firmly detected. Owing to its short photochemical lifetime ( ∼ 300 years), the existence of significant methane would indicate recent release from sub-surface reservoirs; a quantitative measure of the release rate could be inferred from its present atmospheric abundance. Sub-surface methane could be primordial (reduced cosmogonic carbon) (1) or biotic in origin (4); local enhancements are expected if methane is released from discrete regions. The presence of sub-surface hydrogen concentrations on Mars has been inferred from local-enhancements in epithermal neutron fluxes measured on Mars Odyssey (5), however, independent evidence is required to establish its likely chemical form (e.g., water vs. hydrocarbons) in low-latitude sites (Amazonia Planitia, and Schiaparelli-Cassini). We suggest that enhanced methane there could test whether sub-surface hydrogen is chemically bound in hydrocarbon moieties. In any case, a quantitative measure of methane production would provide a key for assessing models of biogenic vs. primordial origins.

We conducted a deep search for methane on Mars using state-of-the-art infrared spectrometers. The R0 and R1 lines in the ν ₃ vibrational band near 3.3 μ m were searched using CSHELL at the NASA IRTF (Jan. and March 2003), and Phoenix at Gemini South (May 2003). Details will be presented along with preliminary results.

This work was supported by NASA RTOP 344-32-30-10 to MJM, and NSF RUI Grant AST-0205397to REN.

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