It's the most precise calculation yet for the thickness of the red planet's ice, according to the international team of researchers responsible for the discovery.
Using an ice-penetrating radar to map the south pole's underlying terrain, the scientists calculated that the ice is up to 2.2 miles (3,500 meters) thick in places, said the study's leader, Jeffrey Plaut of NASA's Jet Propulsion Laboratory in Pasadena, California.
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| ©NASA/JPL/ASI/ESA/Univ. of Rome/MOLA Science Team/USGS |
| A new radar survey of Mars's south pole (seen in true color, inset) has shown that its ice cap is thicker and wider than previously suspected. In fact, scientists say, the pole contains enough ice to flood the entire planet's surface with 36 feet (11 meters) of water if melted. The ice is also far more pure than scientists had expected. |
The radar, from the Mars Express orbiter, also revealed the surprising purity of the ice, Plaut added.
On average, the ice cap contained less than 10 percent dust, he said. The study will appear in tomorrow's issue of the journal Science.
A Solid Find
The polar ice cap may also contain some frozen carbon dioxide, or dry ice, Plaut said. But there can't be much of it, because such a thick layer of dry ice would start to ooze sideways under its own weight.
"Only water ice could support itself that way," Plaut said.
The research team also found a series of depressions buried beneath the ice only 180 miles (300 kilometers) from the pole.
These are probably impact craters, Plaut said, though they might also be features caused by erosion, similar to ones found elsewhere on Mars.
"We don't completely understand them, because we have only a vague image of them," Plaut said.
But, significantly, the team didn't find a large depression under the ice.
On Earth such depressions occur beneath ice caps because the weight of the ice pushes the underlying crust down into the planet's mantle, like a sleeper's head depressing a pillow.
"On Mars this is not taking place," Plaut said. "This tells us that the upper crust and mantle of Mars is very stiff - much stiffer than the Earth."
Missing Water
The amount of water in the ice cap is more than most scientists had expected, but not by a huge amount.
And even when combined with the amount believed to reside at the planet's north pole, it's still only a small fraction of the water that scientists believe once existed on the red planet.
There are only two places where the rest can be: buried underground or lost to space through the thin Martian atmosphere.
"Those are still avenues that are being investigated," Plaut said.
Ray Arvidson, a professor at Washington University in St. Louis, Missouri, and a member of the Mars rover team, says that the new find is simply another part of scientists' expanding efforts to trace the missing Martian water.
Other orbiting instruments are looking for ice in the Martian soil, while the Mars rovers and additional instruments are mapping out deposits of water-altered minerals on the Martian surface.
Years ago, Arvidson said, Mars researchers could only speculate about water based on ancient river channels and canyons. But now it's possible to look for it directly.
"The more we look, the more water we're seeing," Arvidson said. "It's really exciting."
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