Dione Close Up


Dione chasmsSome parts of the surface of Saturn’s moon Dione are covered by linear features, called chasmata, in dramatic contrast to the round impact craters that cover most moons. The bright network of fractures on Dione was seen in poor resolution Voyager images and was called “wispy terrain.” The actual nature of this terrain was unclear until Cassini photos showed we weren’t seeing something like surface deposits of frost but a pattern of bright icy cliffs among myriad fractures. This stress pattern may be related to Dione’s orbital evolution and the effect of tidal stresses over time.

Image Credit: NASA

Dione and Mimas


Dione_MimasBecause of the illumination angle, Mimas (right) and Dione (left) appear to be staring up at Saturn looming in the background of this image captured by the Cassini spacecraft.

Although certainly large enough to be noticeable, moons like Mimas (396 km across) and Dione (1123 km across) are tiny compared to Saturn (120,700 km across). Even the enormous moon Titan (5,150 kilometers across, larger than the planet Mercury) would be dwarfed by the giant planet in such a picture.

Image Credit: NASA

Moons


moons_SaturnRhea, Enceladus, and Dione are three of Saturn’s moons.  This is what they looked like as seen from the Cassini spacecraft on 25 April, 2011. Saturn is also present in the picture on the left but is too dark to see. Rhea is closest to Cassini. It is the largest moon in center of the image. Enceladus is to the right of Rhea. Dione is to the left of Rhea and is partially covered by Saturn.

Image Credit:  NASA

Moons!


When making its closest pass yet to Saturn’s moon Dione late last year, the Cassini spacecraft took this picture of the moon Dione with Saturn’s rings and the two small moons Epimetheus and Prometheus in the background. The heavily cratered snow-white surface of the 1,100 km wide Dione makes quite a contrast with the comparative darkness of the smaller moon Epimetheus. The image was taken when Cassini was only about 100,000 km from the large icy moon.

Dione was discovered by the astronomer Cassini in 1684. It is named after the titan Dione of Greek mythology. Epimetheus is co-orbital (it shares its orbit) with another of Saturn’s moons Janus. Astronomers did not realize that they were actually seeing two objects in the same orbit until 1978. Prometheus was discovered in 1980 in images taken by Voyager 1.

Image Credit: NASA