GREENBELT, Md., Jan. 25 (UPI) -- NASA says data from its Dawn mission to the asteroid Vesta suggests the rocky body is cold and dark enough to have retained ice for billions of years.

Modeling of Vesta's average global temperatures and illumination by the sun shows that, under present conditions, Vesta's polar regions are cold enough to sustain water ice for long periods, the space agency said in a release Wednesday.


Though generally believed to be quite dry, roughly half of the giant asteroid is expected to be so cold and to receive so little sunlight that water ice could have survived there, it said.

"Near the north and south poles, the conditions appear to be favorable for water ice to exist beneath the surface," Timothy Stubbs of NASA's Goddard Space Flight Center in Greenbelt, Md., said.

The presence or absence of water ice on Vesta would provide clues about the tiny world's formation and evolution, its history of bombardment by comets and other objects, and its interaction with the space environment, researchers said.

The model predicts that the average annual temperature near Vesta's north and south poles is less than minus 200 degrees Fahrenheit, a critical temperature below which water ice is thought to be able to survive in the top 10 feet or so of the soil, called regolith.

"On average, it's colder at Vesta's poles than near its equator, so in that sense, they are good places to sustain water ice," Stubbs said. "But they also see sunlight for long periods of time during the summer seasons, which isn't so good for sustaining ice. So if water ice exists in those regions, it may be buried beneath a relatively deep layer of dry regolith."