Final proof that Mars has bred life will be confirmed this year, leading NASA experts believe. The historic discovery will come not on Mars itself but from chunks of the red planet here on Earth.
David McKay, chief of astrobiology at NASA's Johnson Space Centre in Houston, says powerful new microscopes and other instruments will establish whether features in martian meteorites are alien fossils.
He says evidence for life in the space rocks could have been claimed by the UK if British scientists had used readily-available electron microscopes. Instead, images of colonies of martian bacteria were collected by American scientists.
The NASA team is already convinced that colonies of micro-organisms are visible inside three martian rocks that landed on Earth. If so, this would have profound implications for our understanding of life in the universe.
Two of the meteorites - ALH84001 and Yamato 593 - were found in the Antarctic by American and Japanese scientists after they lay in the icy desert for thousands of years.
But of special interest is a meteorite that fell in many chunks at Nakhla, Egypt, in 1911. Most of the fragments ended up in London's Natural History Museum.
The stones are known to be from Mars because gases trapped inside them match those in rocks examined by probes on the red planet. They were blasted out of its surface by asteroid impacts and then drifted around the solar system for millions of years before falling to earth.
One of the new instruments that will analyse the meteorite will bombard it with a stream of ions to check whether features are geological or biological.
The NASA team believes a planet-wide network of micro-organisms came to life underground on Mars 3.6 billion years ago when the planet was much warmer and wetter with a much thicker atmosphere. Simple life was developing on Earth around the same time.
McKay says it is remarkable that some of the most striking new evidence for life on Mars has been sitting in London for nearly 100 years.
He told the website Spaceflight Now that if British researchers had examined their Nakhla meteorite with readily available electron microscopes and other tools like those used by the U.S. team, the new evidence for life on Mars could have been a British discovery, rather than an American one.
He added: "We do not yet believe that we have rigorously proven there is - or was - life on Mars. But we do believe that we are very, very close to proving there is or has been life there."
Compelling evidence that life may still survive today on Mars was revealed a year ago after NASA detected plumes of methane in the planet's atmosphere.
Picture: A close-up of the "colony of martian bacteria" revealed though a microscope in the Nakhla meteorite. (NASA)
* Discover space for yourself and do fun science with a telescope. Here is Skymania's advice on how to choose a telescope. We also have a guide to the different types of telescope available.