Ocean on Mars is Frozen Undergound

For decades, scientists have pondered the mystery of the waters of Mars, which once covered much of the surface of the planet: where did they go?

Finally, they may have the answer in an announcement that will fuel the debate about life on the planet. Nasa chiefs are preparing to announce the discovery of an ocean frozen beneath the soil of the red planet.

The telltale sign of subterranean hydrogen in huge quantities near the Martian south pole was discovered by scientists monitoring their Mars Odyssey orbiter. Many believe that so much hydrogen could only exist in molecules of water.

Researchers have speculated that Mars may once have been awash with rivers, lakes and seas. If water once existed on Mars, it would also have had a denser atmosphere - and been a potential home for life.

The discovery, expected to be outlined in the magazine Science this week, heightens the challenge for the next mission to the planet. The European Mars Express, which will be launched in June 2003, will also carry the British lander Beagle 2, designed by a team led by Colin Pillinger of the Open University. It could touch down in December. A pair of Nasa landers will arrive shortly afterwards.

The Beagle 2 instrument - with a colour calibration chart supplied by the artist Damien Hirst, and a call sign composed by Damon Albarn of Blur - is also equipped to "sniff" for organic chemicals that might be a clue to the presence of organisms below the surface.

The belief is that some cataclysm stripped the red planet of much of its envelope of atmosphere billions of years ago, and left it frozen, arid and lifeless. When the first Viking probe landed on Mars in 1976, scientists looking for other forms of life in the solar system gave up - only to see the debate reawakened in 1996 by the discovery of what seemed to be fossilised microbial life in a meteorite known to have come from Mars.

The confirmation of water on Mars could open the way for serious human exploration. Both European and US scientists believe a manned mission could take place within two decades.