NASA studies Mars' arctic soil

PASADENA, Calif., Dec. 16 (UPI) -- The U.S. space agency says martian soil its Phoenix Mars Lander collected this year is very cold and dry, but during climate cycles it might become moist.

"Phoenix found clues increasing scientists' confidence in predictive models about water vapor moving through the soil between the atmosphere and subsurface water-ice," the National Aeronautics and Space Administration said, noting the models predict the vapor flow can wet the soil when the tilt of Mars' axis, the obliquity, is greater than it is now.

With no large moon to stabilize it, Mars goes through periodic cycles when its tilt becomes much greater than Earth's, scientists said, with the arctic plain where Phoenix worked experiencing warmer summers.

"The ice under the soil around Phoenix is not a sealed-off deposit left from some ancient ocean," said Ray Arvidson of Washington University in St. Louis. "It is in equilibrium with the environment, and the environment changes with the obliquity cycles on scales from hundreds of thousands of years to a few million years."

The findings were presented this week in San Francisco during a meeting of the American Geophysical Union.