European scientists have found what they believe is a dust-covered, frozen sea near the equator of Mars, raising the possibility that liquid water may still exist on Mars, locked under 90 feet of ice.

Scientists long have known that there is water ice at the poles, but found only hints that it once existed near the equator. This discovery shows it may have existed there recently, that the ice could still remain, and that liquid water from underground aquifers may lurk somewhere under it still.

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Attention was drawn to the region, roughly the size of the Great Lakes, by formations near the equator that look like pack ice near the Earth's poles. Further bolstering the theory, they occur in a region as smooth — geologically speaking — as a skating rink.

Cracked and drifting beneath a dusting of orange soil, floes of what could be water ice range from plates the size of suburban back yards to enormous chunks 18 miles across.

The way that the floes drift, breaking into pieces and forming pressure ridges as they grind into each other, suggests characteristics similar to ice moving on fluid water.

The findings emerged in three-dimensional images taken by the European Space Agency's Mars Express orbiter last year.

The paper announcing the findings was released Monday at the ESA's Mars Science Conference in the Netherlands after 13 months of secrecy. It is expected to be published next month in the journal Nature, Muller said.

"We've never seen anything like pack ice before, nothing that ever before seemed like an enormous pool of water," said Jan-Peter Muller, a professor of Geomatic Engineering at University College London and a co-author in the study.

The subject of liquid water — past or present — is a controversial one among Mars researchers.

Though numerous probes from both NASA and the ESA have looked for signs of water in Mars' equatorial region, definitive evidence has yet to be uncovered.

If the results are born out, that evidence may well lie in Mars' Elysium region, where the Europeans found the floes near a set of well-known fissures called the Cerberus Fossae.

The water is believed to have originated beneath the surface of Mars, then gushed forth in a catastrophic flood after being warmed by the planet's core.

"These are pieces of a puzzle. We're not really sure what it's going to look like at the end, but it's coming into focus," said NASA chief scientist James Garvin, recently promoted from a post as the space agency's lead scientist for Mars and Earth's moon.

He said Muller and co-authors John Murray of the Open University and Gerhard Neukum of the Free University of Berlin "have put together a story that seems to hold — pardon the pun — some water now. But this is the first piece of a puzzle."

Mars Express will test the area with ground-penetrating radar in May. NASA's Mars Reconnaissance Orbiter launches in August.

But by studying floes, impact craters and apparent pressure ridges in the area, Muller and his co-investigators said the features near the equator in Mars' northern hemisphere are consistent with water that froze into sheets of ice 130 feet thick. Since that time, nearly 5 million years ago, the ice has since shrunk to an average of 90 feet, their calculations show.

It should have shrunk much more. At Mars' low atmospheric pressure, water ice evaporates straight from ice to a gaseous state, like dry ice on Earth.

The ESA scientists believe it didn't in this case because at the same time that a titanic flood belched forth a small sea from Mars' innards, volcanic ash also erupted from the Cerberus Fossae, forming "a substantial protective layer on the ice," the report reads.

Still unanswered is what happened to the proposed water, which would be locked beneath the suspected ice cap and its protective blanket of ash.