Mars orbiter points to gigantic frozen sea

LONDON - A vast expanse of frozen sea may lie just beneath the surface of the Martian equator, researchers say.

Images reveal a series of raft-like "plates" resembling ice formations covering an area 800km by 900km and 34m deep in the equatorial region known as Elysium.

The pictures indicate the first discovery of a large body of water beyond the planet's polar icecaps, confirming evidence that free water existed in the past.

Scientists believe that a catastrophic event may have flooded the landscape five million years ago before it froze over, resulting in a submerged sea of ice.

"It's been predicted for a long time that you should find water close to the surface of Mars near the equator," said Professor Jan-Peter Muller, of University College London. "This is an area where there are a lot of river features, but no one has ever seen a sea before, and certainly no one has ever seen pack ice before."

The discovery, published this week in Nature and New Scientist magazines, was made by a team of international scientists led by John Murray of Britain's Open University.

The pictures were taken from the high-resolution stereo camera on the European Space Agency's Mars Express, which has been orbiting the Red Planet since December 2003.

Scientists analysing the craters found that they were shallow, which suggested that they had been filled up with ice, while the surface remained unusually level.

The ice is believed to have been covered by a layer of dust and volcanic ash which has prevented it from melting due to its proximity to the Martian equator.

Researchers found that the plates do not appear to consist of solidified lava, which is how similar formations have previously been explained. Instead, they stated that their size and characteristics "imply an extremely mobile fluid, with similar characteristics to water".

"The story runs that water flowed in some kind of massive catastrophic event; pack ice formed on top of that water and broke up, and then the whole thing froze rigid," Muller told the BBC. "Large amounts of dust then fell over that area. The dust fell through the water and on top of the pack ice, which explains why the pack ice is a different hue to the area around it."

Further investigation is now required to support the initial findings, according to the researchers, who will present their findings at the Lunar and Planetary Science Conference in Texas next month.

Michael Carr, a specialist on Martian water at the US Geological Survey in California, who was not part of the team, described the conclusions of the latest research as "fairly plausible".

However, he emphasised the fact that there is very little water vapour in the Martian atmosphere; he claims that this would make it difficult to prove if the frozen sea exists.

He told New Scientist: "We know where the water came from ... You can trace the valleys carved by water down to this area."

- INDEPENDENT