Measuring methane and its isotopes ^12CH_4, ^13CH_4, and CH_3D on the surface of Mars with in situ laser spectroscopy

In light of the recent discovery of methane on Mars and its possible biological origin, a strategy is described for making in situ measurements of methane and its isotopes on the surface of Mars by laser spectroscopy in the 3.3-μm wavelength region. An instrument of reasonable mass (~1 lb) and power (few watts) is capable of measuring mixing ratios down to 0.1 part per 109 by volume, a hundred times lower than recently reported observations. Making accurate measurements of 13CH4 and CH3D will be more difficult. For measuring 313C to 10‰ and δD to 50‰, sample preconcentration will be required to ~3 parts per 106 by volume for δ13C and to ~40 parts per 106 by volume for δD. This need would be mitigated by the discovery of larger local abundances of methane near the source regions.