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NASA Rover Fails to Turn Up Methane On Mars
The Washington Post is one of many sources to report the possibly disappointing news that NASA's Curiosity rover has failed to find any methane on Mars. "[NASA planetary scientist Michael] Mumma had high hopes for a positive result because he and his colleagues believe they have detected methane on Mars remotely, from telescopes on Earth that can discern the chemical nature of Mars’s atmosphere. A European orbiter around Mars also spotted methane. But the methane has proved ephemeral — now you see it, now you don’t. Mumma said he and his colleagues are reviewing their work to see if there is some error in the mix. Perhaps the methane simply disappears quickly on Mars, through some unknown chemical process. 'It’s possible that we don’t understand something that’s going on in the Martian atmosphere,' said Michael Meyer, lead scientist for NASA’s Mars Exploration Program.'"
The problem with the satellite observation lies with the low resolution of the instrument used for the detection: the methane bands were not observed directly.
Without going into the details, we can say that the error bars were pretty high on that observations.
So, these results by Curiosity are not really unexpected, nor dissatisfactory: they match very well with the understanding of the CH4 chemistry!
An interesting paper was published on that subject by Zahnle in 2011 : http://faculty.washington.edu/dcatling/Zahnle2011_Mars_CH4_Doubts.pdf