Saturn moon is a frigid world


Dione an 'older, more mature moon,' says Cassini scientist

Wednesday, October 19, 2005 Posted: 1533 GMT (2333 HKT)

Saturn's moon Dione, with Saturn in the background, as photographed by Cassini October 11.

LOS ANGELES, California (AP) -- A close flyby of Saturn's grayish moon Dione reveals it is a mature, frigid world with hints of tectonic activity, new observations suggest.

The U.S.-European Cassini spacecraft flew within 310 miles (500 kilometers) of the Dione's pale surface last week, showing it possessed a heavily cratered surface but no presence of an atmosphere.

Cassini scientists compared the frozen Dione to another Saturn moon, Enceladus, which recently was found to have active ice volcanoes and a significant atmosphere.

"Dione seems to be an older sibling of Enceladus," said Bonnie Buratti, a Cassini scientist. "Enceladus is the up-and-coming moon, complete with a recently active history, while Dione is the older, more mature moon."

Orbiting Saturn within the tenuous E-ring, Dione possesses fine streaks that crosscut its surface. Parallel grooves splash across the terrain, which are interrupted by larger, asymmetrical bright fractures. Scientists believe the cracks and fractures were caused by tectonic activity.