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Saturn
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Saturn Summary

Saturn

Saturn Moon: Dione!

This image of Dione was taken by Voyager 1 on November 12, 1980. It shows the Saturn-facing hemisphere.


Discovered in 1684 by the Italian-French astronomer Gian Domenico Cassini, Dione is an icy and dense moon composed of a rocky core with large amounts of water and ice. It is tidally locked to Jupiter as reflected by data from albedo observations and has a mixture of cratered plains ranging from 30 kilometers to 100 kilometers in diameter. Most of the heavily cratered plains lie in the trailing hemisphere while the less cratered plains lie in the leading hemisphere. This fact was somewhat of a surprise to scientists since it was the exact opposite of what they had expected. If Dione had its heavily cratered plains in the trailing hemisphere and the less cratered plains in the leading hemisphere, that means it must have been tidally locked to Saturn in the opposite direction. Shoemaker and Wolfe had proposed this model and further theorized that this was caused by an impact that left a 35-kilometer (21-mile) crater to spin the moon.

Many large impact craters are seen in this view of the Saturnian moon Dione taken by NASA's Voyager 1 on Nov. 12, 1980 from a range of about 240,000 kilometers.


Aside from Titan, Dione is the densest of Saturn's satellites. Most of the satellite is composed of water and ice (66%), with the rest rocky material (33%). The satellite also has bright misty material on its surface that is somewhat transparent. The exact origin of this material is unknown but it could be snow or ash from the moon's surface. Another moon, Helene, is co-orbital with Dione; that is, it orbits Saturn at the same distance as Dione, and precedes Dione by about 60 degrees.

Voyager l image from a range of 790,000 kilometers of Dione.


Circular impact craters up to about l00 kilometers in diameter are seen in this view of Saturn's icy moon Dione. The image was taken by Voyager l from a range of 790,000 kilometers at 2:20 a.m. PST on November l2. Bright, whispy markings form complex arcuate patterns on the surface. These markings are slightly brighter than the brightest features seen by Voyager on Jupiter's moons, suggesting that they are surface frost deposits. The patterns of the bright bands hint at an origin due to internal geologic activity, but the resolution is not yet sufficient to prove or disprove this idea. Dione's diameter is only ll00 kilometers, much smaller than any of Jupiter's icy moons. It thus belongs to a class of small, icy objects never observed before the Voyager I Saturn encounter. The view here is of the face which trails in orbit.


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