Cold planet Mars.

Nature reveals a setback in the search for life on Mars. We’re learning more about the atmosphere there, and there doesn’t seem to be enough methane:

On Earth, life is responsible for the vast majority of the planet’s atmospheric methane, which exists at levels of about 1,700 parts per billion. If methane were detected on Mars, microbes could thus be invoked as its source, although trace amounts could also be produced through comet impacts or chemical reactions underground that involve rocks and hot water.

Various experiments in the past decade have claimed to detect Martian methane at levels as high as 30 parts per billion1 and 45 parts per billion2. But more perplexing was the way in which some of the methane signals appeared as hotspots, or plumes, and then disappeared — implying both a sudden injection, as well as a process that would quickly destroy the methane, which would otherwise mix in the atmosphere and persist.

The team has used the instrument four times, and on the first two occasions, a large methane signal — of 7 or 8 parts per billion — was present. The team quickly realized that it was due to contamination by residual Earth air in the device.

Some folks are saying Gale Crater’s not the best place to look for methane plumes. There may be better sites elsewhere… or there may not.