Shadows cast by Saturn’s rings darken the planet’s southern hemisphere and cause the truncated appearance to the bottom of this image taken by the Cassini spacecraft. Saturn’s moon Tethys is is in the foreground on the right. The smaller moon Epimetheus can be seen below the center of the image.
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.
NASA’s Cassini spacecraft obtained this unprocessed image on 12 December, 2011. The camera was pointing toward Saturn’s moon Dione from approximately 70,000 miles (113,000 kilometers) away. The smaller moons Epimetheus and Pandora are also visible along with Saturn’s rings.