LOS ANGELES - 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 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.
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Cassini mission: http://saturn.jpl.nasa.gov
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