An ocean of liquid water may lie below the icy, battered crust of Jupiter’s moon Callisto, which is shown in a composite image from the Voyager 1 spacecraft. The most prominent feature in the image is Valhalla, an ancient impact crater. The bright rings extend about 900 miles (1,500 km) from the center of the crater. [NASA/JPL]
Find out more in our radio program entitled Moon and Jupiter.