Feb. 22 (Bloomberg) -- The European Space Agency's Mars Express orbiter has discovered a frozen sea under the surface near the red planet's equator, raising the possibility that life may exist there, mission scientists said.

The sea appears to have formed from water that came from below the planet's surface about 5 million years ago and now survives as ice under a layer of dust and volcanic ash, University College London, one of three institutions leading studies on the craft's high resolution stereo camera instrument, said today in an e-mailed statement.

Higher levels of methane gas over the same area suggest that ``primitive'' organisms might survive on Mars today, UCL said, adding that further research to confirm the presence of ice beneath the surface will be carried out by a Mars Express radar that will be deployed in May. Methane on Earth is produced as a by-product of the metabolism of many organisms.

``The fact that there have been warm and wet places beneath the surface of Mars since before life began on Earth, and that some are probably still there, means that there is a possibility that primitive micro-organisms survive on Mars today,'' John Murray at the U.K.'s Open University said in the statement. ``This mission has changed many of my long-held opinions about Mars -- we now have to go there and check it out.''

North Sea

The body of water collected in an area about the size of the Earth's North Sea, to a depth of an average 45 meters (148 feet), UCL said. When water levels sank, pack ice seems to have grounded on islands, and thick ice formed in craters, UCL said. The flat surface of the planet in the area studied ``suggests that most of the ice is still there,'' the university added.

Ice on the surface of Mars isn't stable because of the planet's low atmospheric pressure, UCL said. While frozen water would normally sublime -- or change straight from a solid state into vapor -- on the planet's surface, the frozen sea is protected from this process by a covering of dust and ash, the university added.

The camera is capturing three-dimensional images of Mars as part of a project to map the planet. The camera's images provide scientists with information on the climate and presence of water and volcanic activity on Mars, as well as helping to date features on the red planet by measuring craters. The instrument is also observing Mars's two moons, Phobos and Deimos.

Martian Years

Mars Express was launched in June 2003 and reached the planet on Dec. 25 that year, with a mission lifeline scheduled to last a Martian year (687 Earth days) from then. Pending further funding, the 300 million-euro ($380 million) mission is designed to last a further Martian year after that.

Mars Express and NASA's two rovers on Mars, Spirit and Opportunity, have discovered ice at the planet's poles and evidence that water once flowed there. Scientists have said they hope the MARSIS radar might uncover evidence of liquid water under the surface of the planet, paving the way for future manned missions to Mars.

ESA on Feb. 8 said it had decided to go ahead with a deployment in May of MARSIS after concluding that the maneuver, which has the potential to damage the orbiter, won't cripple the mission.

Murray and Jan-Peter Muller at UCL are co-investigators on the camera instrument, in a team comprising scientists from 10 countries and led by Gerhard Neukum of the Free University of Berlin. Their findings were announced yesterday at a conference at ESA's European Space Research and Technology Center in Noordwijk, the Netherlands. They will publish a paper on the discovery in the journal Nature on March 17.

To contact the reporter on this story: Alex Morales in London at amorales2@bloomberg.net.

Last Updated: February 22, 2005 12:14 EST