Towards the end of 2011 a large and hugely expensive robotic rover called Curiosity is due to blast off for Mars from Cape Canaveral. If it makes it safely to the planet’s surface in August 2012 (getting down from orbit in one piece has not always proved easy for space probes) one of the first things it will do is sniff the air. Its creators, back on Earth, will be straining to see if that air carries a whiff of methane.
In 2004 three different groups said they had seen signs of methane in the atmosphere of Mars. Since, on Earth, almost all atmospheric methane comes from living things, this provided the biggest news from the planet since ALH 84001, a meteorite purportedly bearing Martian fossils, created headlines in 1996.
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