"It was detected by telescopes on Earth and has recently been confirmed by instruments onboard the European Space Agency's orbiting Mars Express craft.
Methane lives for a short time in the Martian atmosphere so it must be being constantly replenished.
There are two possible sources: either active volcanoes, none of which have been found yet on Mars, or microbes."
"Most astronomers agree that Mars could be turned into a little Earth, though it would take decades to achieve this goal and would require massive expenditure. But many scientists are horrified by the concept.
'The idea of terraforming Mars is extreme, but it is not cranky - that is the truly horrible thing about it,' said Paul Murdin, of the Institute of Astronomy, Cambridge. 'If it was just a silly science-fiction notion, you could laugh it off. But the idea is terribly real. That is why it is dreadful. We are mucking up this world at an incredible pace at the same time that we are talking about screwing up another planet.'
Over the past months, astronomers have become increasingly confident they will find Martian lifeforms after decades of disappointment. Europe's Mars Express and America's two robot rovers, Spirit and Opportunity - which are all investigating the planet at present - have detected strong evidence that water, mixed with soil, exists in large amounts on Mars. "