Ocean inside Jupiter’s outermost moon may have cushioned heavy impact

The Associated Press
Friday November 30, 2001

PASADENA — Recent photographs from NASA’s Galileo spacecraft provide supporting evidence to the theory that Callisto, Jupiter’s outermost moon, may hold an underground ocean, scientists said Thursday. 

Callisto, one of four large moons surrounding Jupiter, can be seen to have a surface that sits directly opposite from its Valhalla basin, which was rocked by a collision with a major object. 

The images were taken during a May 25 flyby. 

“The opposition point shows no effect from the impact,” the National Aeronautics and Space Administration’s Jet Propulsion Laboratory said in a statement. 

Areas that sit opposite similar points of impact on Mercury and the Earth’s moon show lumpy terrain directly attributed to seismic activity from powerful impacts. 

The new discovery parallels a 1990’s model, which proposed that a liquid layer inside Callisto could cushion shock on the outside, said planetary geologist David A. Williams of Arizona State University. 

“Although there is a lot of uncertainty in the computer modeling of Callisto, it’s good that this image supports the hypothesis presented a decade ago,” Williams said Thursday. 

He cautioned, however, 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,” he said.