Dense Ice Revealed at Mars' South Pole

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March 15, 2007 — Radar scans of Mars have unveiled a vast reservoir of nearly pure frozen water around the planet's south pole, a deposit so rich that if it were spread evenly on the surface it would be 36 feet deep.

Work to map ice deposits on the planet's north pole are under way, but even if they matched the amount found in the south that would still be only a small fraction of the water scientists estimate Mars once had, said planetary scientist Jeff Plaut with NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Using a radar instrument on the European Space Agency's Mars Express orbiter, Plaut and an international team of 23 scientists found layered deposits of ice beneath and beyond a thin cap of frozen carbon dioxide and water at Mars' south pole. The deposits are believed to be at least 90 percent frozen water.

The scientists also found buried depressions in the ice, some as deep as 0.6 miles, that may be old impact craters.

Overall, the ice, which covers an area larger than Texas, is unevenly deposited, with sections as deep as 2.3 miles, the researchers report in this week's issue of the journal Science.

The finding raises questions about why the underlying terrain is so variable in depth. The Mars Express radar data also show streaks of a highly reflective substance, which if the environment were warmer would likely be interpreted as liquid water.

"Many ice bodies on the Earth where they contact with a rock base there is a liquid layer, but the thermal models on Mars argue against that," Plaut said in an interview. " The radar evidence doesn't compel us to come to that conclusion."

For one thing, the radar data shows the bright streaks coming nearly to the planet's surface. "It seems like it would be physically impossible (to have liquid water in that area) but we're not completely ruling it out," he said.

For now, it's one of the many question marks that dot Mars research initiatives. Scientists still can't explain what happened to all the water that must have been needed to carve Mars' surface features.

NASA has been focused on studying the planet's water history in hopes of answering an even more provocative question of whether life ever arose on Mars.

Mars Express mapped Mars' southern polar regions for four months beginning in late 2005. The scientists' findings are based on 1,800 individual measurements made during 60 orbits of the planet.

Additional studies are planned using a higher frequency radar sounder on NASA's Mars Reconnaissance Orbiter, which began science operations in November.