Dione (moon)
Dione is a moon of Saturn, discovered in 1684 by Giovanni Cassini. It is the fourth-largest moon of Saturn, and the 15th-largest moon in the Solar System. Dione is primarily composed of water ice, with a significant fraction of rock material. Its surface is heavily cratered, indicating a long history of impacts.
Physical Characteristics:
Dione has a diameter of approximately 1,123 kilometers (698 miles). Its density is about 1.48 g/cm³, suggesting that it is about one-third rock and two-thirds water ice. Dione is tidally locked to Saturn, meaning that one side always faces the planet.
Surface Features:
Dione's surface exhibits a variety of features, including:
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Impact Craters: The surface is heavily cratered, particularly in the trailing hemisphere (the side facing away from Saturn). Some craters are hundreds of kilometers in diameter.
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Wispy Terrain (Linea): Dione is notable for its bright, linear streaks of material that crisscross its surface. These "wispy terrains" were originally thought to be ice cliffs created by tectonic activity. However, observations from the Cassini spacecraft suggest that they are actually bright ice deposits associated with fractures and ridges.
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Chasmata: Long, deep canyons or troughs that stretch across the surface. These are believed to be the result of tectonic activity or extensional stresses.
Orbit and Rotation:
Dione orbits Saturn at a distance of approximately 377,400 kilometers (234,500 miles), completing one orbit in about 2.7 Earth days. As mentioned previously, it is tidally locked.
Atmosphere and Magnetosphere:
Dione has a very tenuous atmosphere, primarily composed of oxygen ions. It interacts with Saturn's magnetosphere, resulting in the formation of a plasma wake downstream from the moon.
Exploration:
The Cassini spacecraft performed multiple flybys of Dione, providing detailed images and data about its surface, composition, and environment. These observations have significantly improved our understanding of Dione and its role in the Saturnian system.