The Cassini spacecraft snapped this picture of the moon Dione orbiting Saturn. At 1122 km in diameter, Dione is the 15th largest moon in the Solar System. Its interior is probably a combination of equal masses of silicate rock and water ice.
Shape and gravity observations collected by Cassini suggest the moon has a core of around 400 km of rock surrounded by a roughly 160 km envelope of water, probably in the form of ice. However, some models suggest the lowermost part of this layer could be in the form of an internal liquid salt water ocean.
Image Cedit: NASA