Nasa rover's failure to find methane means life on Mars is less likely

In findings that are as scientifically significant as they are crushing to the popular imagination, Nasa has reported that its Mars rover, Curiosity, has found no evidence that life could be thriving on Mars today.

Curiosity has been trundling across the red planet for a little over a year looking for methane, a gas considered a possible calling card of microbes. So far it has found none of it.

The conclusion was published in the journal Science.

While the absence of methane does not entirely preclude the possibility of life on Mars - there are plenty of microbes on Earth that do not produce methane - it does return the idea to the realm of pure speculation without any hopeful data to back it up.

The history of human fascination with the possibility of life on Mars is rich, encompassing works of science fiction, Percival Lowell's romantic efforts to map what turned out to be imaginary canals, Orson Welles' panic-inducing 1938 War of the Worlds radio play, and of course Bugs Bunny's nemesis Marvin the Martian.

But Marvin apparently did not emit enough methane for Curiosity's sensitive instruments to find him.

"You don't have direct evidence that there is microbial process going on," said Sushil Atreya, a professor of atmospheric and space science.