Measuring methane and its isotopes 12CH4, 13CH4, and CH3D 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-microm wavelength region. An instrument of reasonable mass (approximately 1 lb) and power (few watts) is capable of measuring mixing ratios down to 0.1 part per 10(9) by volume, a hundred times lower than recently reported observations. Making accurate measurements of 13CH4 and CH3D will be more difficult. For measuring delta13C to 10/1000 and deltaD to 50/1000, sample preconcentration will be required to approximately 3 parts per 10(6) by volume for delta13C and to approximately 40 parts per 10(6) by volume for deltaD. This need would be mitigated by the discovery of larger local abundances of methane near the source regions.