Report

Low Upper Limit to Methane Abundance on Mars

Science  19 Sep 2013:

DOI: 10.1126/science.1242902

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Abstract

By analogy with Earth, methane in the martian atmosphere is a potential signature of ongoing or past biological activity. During the last decade, Earth-based telescopic observations reported “plumes” of methane of tens of parts-per-billion by volume (ppbv), and those from Mars orbit showed localized patches, prompting speculation of sources from subsurface bacteria or non-biological sources. From in situ measurements made by the Tunable Laser Spectrometer (TLS) on Curiosity using a distinctive spectral pattern unique to methane, we here report no detection of atmospheric methane with a measured value of 0.18 ±0.67 ppbv corresponding to an upper limit of only 1.3 ppbv (95% confidence level) that reduces the probability of current methanogenic microbial activity on Mars, and limits the recent contribution from extraplanetary and geologic sources.

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