Pics suggest deep ocean in Jupiter moon

A heavily cratered portion of the surface of Callisto in an image taken by the Galilieo spacecraft.

PASADENA, California -- New close-up pictures from a deep space probe offer tantalizing evidence that one of Jupiter's largest moons contains a sizable ocean in its interior, scientists said this week.

Callisto, the outermost of four large jovian satellites, was rocked in the past by a collision in an area known as the Valhalla basin.

Newly released images of the region directly opposite the basin, which Galileo took when it flew by Callisto in May, suggest that an underground ocean cushioned the blow of the impact, NASA planetary geologists said.

"The opposition point shows no effect from the impact," NASA's Jet Propulsion Laboratory said in a statement.

Other bodies such as the moon and Mercury have similar impact basins. But unlike Callisto, they have grooved and hilly terrain on the other side, attributed to intense seismic shocks from the collisions. Planetary geologists theorize that those bodies do not have underground reservoirs to soften the blow.

Galileo snapped the photographs in May when it flew to within 20,000 miles (32,000 km) of Callisto, an icy, rocky moon that is the most heavily cratered in the solar system.

The new discovery parallels a 1990s theory that a liquid layer inside Callisto could cushion collisions on the exterior, according to David A. Williams of Arizona State University. But he cautioned that the photos are not proof of an ocean.

"A lot more evidence needs to be uncovered before we will know for sure whether Callisto has a subsurface ocean," the planetary geologist told the Associated Press.