(Related: "Mars's Ice Patchy, Water Cycle Quite Active, Study Reveals" [May 2, 2007].)
"Water vapor in the air basically diffused into the subsurface through pores in the soil and filled up that pore space with ice. It goes away by the same process—it heats up and goes from solid to gas and diffuses back out of the rock."
Schörghofer's theory may therefore reveal a very different recent history for the red planet than once thought.
"The surprise is how frequent Mars's ice ages are and how young some of the ice is," Schörghofer said. "[Some may be] only half a million years old, which is not very old for Mars because most of the surface is billions of years old."
Mars, like all planets, experiences small "wobbles" in its axis as it orbits the sun.
Such variations change the amount of sunlight falling on a planet's surface, which can cause major climate shifts, Schörghofer said.
Earth's wobbles, known as Milankovitch cycles, occur in 20,000- and 100,000-year periods and are thought to impact the waxing and waning of the planet's ice ages.
According to Schörghofer, this means both planets have an ice record that tracks the activity of the sun.
"Mars's ice cores could tell us not only what the climate was on Mars but also changes in the sun, the same solar history that Earth was exposed to," he said.
"Understanding ice ages on Mars is an important step toward understanding the ice record on Mars," he added. "Samples of the Martian ice record could be used to interpret Earth's climate record.
In some ways, the Martian climate is easier to understand and model than Earth's.
Because Mars has no large moon to stabilize its orbit, the planet has much larger wobbles and thus greater climate shifts than Earth.
Mars also has more consistent weather and no oceans.
"Planets are sort of these huge lab experiments that were set up 4.5 billion years ago," Arizona State University's Bandfield said. "[Mars is an opportunity] to test how the physics work on a simpler system and get a better handle on how to apply it to a more complex system."
A first examination of the theory will arrive with the Phoenix lander, already en route to Mars for a 2008 landing. The craft will try to sample Martian ground ice, and the results could make or break Schörghofer's theory. (Related photo gallery: "Phoenix Lander's Search for Mars Water" [August 3, 2007].)
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