NASA’s Mars Curiosity rover has found a small amount of methane wafting over its landing spot in Gale Crater. The levels of the gas occasionally rise tenfold before dissipating again.

The discovery is a significant contribution to the long-running debate over how much of this important gas Mars has.

“Mars is active, both producing and releasing methane,” says Sushil Atreya, a planetary scientist at the University of Michigan in Ann Arbor and co-author of a paper on the findings that is published in Science1. The Curiosity team announced the findings on 16 December in San Francisco, California, at a meeting of the American Geophysical Union.

So far, the scientists do not know where the methane is coming from. “There’s nothing else that correlates with it yet, so it’s hard to tell,” says Michael Meyer, lead scientist for the Mars exploration programme at NASA headquarters in Washington DC.

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