"This is a different beast than the north polar deposits," Phillips said.
The expected layers appear in some places there, he pointed out, but elsewhere the structure looks completely different.
Kathryn Fishbaugh is a planetary scientist at the Smithsonian National Air and Space Museum who was not involved with the new study.
"The new radar results are fascinating and shed an invaluable light on parts of the polar deposits invisible to other instruments without actually drilling into them," she said.
"It will be interesting to see if interpretations of other data yield the same climate change story."
In Deep Water
The study's most surprising finding, though, came in areas where the radar was able to penetrate through 10,000 feet (3,000 meters) of ice all the way to bedrock.
Even in the weak Martian gravity, that much ice should have caused the bedrock to buckle under the load. But it does not, Phillips said, indicating that the crust is thicker or more rigid than previously believed.
This means that the crust is also colder, Phillips added, indicating that liquid water, if it exists, is buried much more deeply than previously suspected. (Related: "Mars's Water Could Be Below Surface, Experts Say" [January 25, 2007].)
"That has implications for all kinds of things, including the depth at which you might find extant life," he said.
The finding also poses problems for astronomers modeling the early years of the solar system. The only way the Martian crust can be that cold and thick is if it's unexpectedly low in heat-generating radioactive elements such as potassium 40, thorium, and uranium.
To date, Phillips said, nobody knows why the planet might have been cheated of such materials when it was forming.
"This tells us that we don't understand [Mars] as well as we thought we did," he said. "This is an amazing thing to say from the fact that the surface doesn't deflect under the ice load, but those are the implications."
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