Saturn's Moon Dione
Written by Fraser Cain
Saturn's moon Dione is one of the 4 moons discovered by Giovanni Cassini in 1671-1684. It's the 4th furthest large moon from Saturn, and the 16th most distant moon over all.
Dione measures 1023 km across, and orbits at an altitude of 377,000 km above the center of Saturn.
It's largely comprised of water ice, but it's more dense than Tethys, so scientists think it has a higher proportion of silicate rock in its interior – it's probably 1/3rd rock.
Dione is tidally locked with Saturn, which means it always displays the same side to the planet. This means that one hemisphere is always leading as it orbits around Saturn, and the other hemisphere is trailing.And like several of Saturn's moons, the leading surface of Dione is different from its trailing hemisphere. The leading hemisphere is heavily cratered and bright, while the trailing side has a network of bright wispy streaks that scientists think are ice cliffs.
These wispy regions were originally a mystery to astronomers. But NASA's Cassini spacecraft made a close flyby on December 13, 2004, and revealed that they're not wispy regions at all, but large cliffs of ice.
Here's an article about Cassini's close flyby of Dione on October 11, 2005, when it passed just 500 km above the surface of the moon, and a color map of the surface of Dione.
Here's some great information on Dione from Solar Views, and more from the Nine Planets.
We have recorded two episodes of Astronomy Cast just about Saturn. The first is Episode 59: Saturn, and the second is Episode 61: Saturn's Moons.
Filed under: Astronomy
