Artwork of Pandora one of Saturn's moon. Pandora together with Prometheus are the so called shepherd moons of the F-ring situated at a distance of 140,600km from Saturn. Saturn's rings are composed of thousands of concentric rings, like grooves on a gramophone record. They are made of billions of ice and rock particles ranging from a few centimetres to hundreds of metres across. Within the rings are larger rocks, known as shepherd moons because their gravity maintains the concentric nature of the ring system. Without these moons, Saturn's rings would have lost their form millions of years ago. The shepherd moons were discovered by the Voyager mission.