A new study of the atmosphere of Mars casts doubt on the enticing possibility that methane plumes emanating from the planet are a signature of microbial life. The researchers found that the variations in methane concentration across Mars could only be explained if the methane produced was quickly broken down by unknown forces, before atmospheric currents could distribute the gas evenly around the planet. But methane is the simplest organic molecule, so if something is destroying it, then other, more complex organic molecules could suffer the same fate [New Scientist].
The mystery began in 2003, when scientists first detected plumes of methane coming from the Martian surface; further observations revealed that the hotspots varied with the Martian seasons. Researchers said the methane could come from volcanic activity, but said it could also, theoretically, be the gaseous excretions of bacteria buried deep underground. To probe the mystery, researchers used a model of the Martian climate that accounted for the chemistry of the atmosphere and its wind patterns, and studied whether the planet’s conditions would allow for the isolated bursts of methane that researchers had previously observed.
The confounding answer, reported in a study in Nature, was that the methane patterns could only be explained by big eruptions of the gas that are completely broken down 600 times faster than methane is destroyed on Earth. Study coauthor Franck Lefevre says that if the findings are confirmed it would mean the Martian surface is very hostile for organics. But this would not necessarily exclude the possibility that life or the remnants of past life persist below ground, where conditions could be more benign [BBC News].
But researchers don’t know what could be breaking down the methane so quickly. Theories range from electrochemical processes caused by dust storms in the atmosphere to a reaction with oxidants, such as hydrogen peroxide or perchlorates, in the soil. In the latter case, the team estimated that methane would only be destroyed in the 10 metres directly above the surface. That limitation means the destruction process would have to be even more extreme – occurring in as little as one hour – to explain the observations. “This would leave little hope that life as we know it can exist at present or that evidence of past life can be preserved in the shallow surface layer,” the authors write [New Scientist].
NASA and the European Space Agency plan to take a closer look at the Martian atmosphere in the next decade. The two agencies have just announced a joint endeavor which includes launching an orbiter in 2016 to study Mars’s methane plumes, and then sending two rovers to the planet in 2018 to seek signs of life. The rovers could be aided by the 2016 orbiter, if it were able to direct the rovers to a landing site near vents of methane, which can be produced by subterranean microbes or by hydrothermal processes on certain volcanic rocks [Nature News].
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Image: NASA / JPL