Moons in the Rings


shepherd_moonsSome of Saturn’s smaller moons are integral with the planet’s rings. These moons create art on a canvas of the rings with gravity as their tool. Here Prometheus is seen sculpting the F ring while Daphnis (smaller than one pixel in this image) raises waves on the edges of the Keeler gap. The image scale is 11 km per pixel.

Prometheus (86 km across) is just above image center; Daphnis (8 km across) is in the Keeler gap just to the right of center and can be located by the waves it creates on the edges of the gap. Prometheus has been brightened to enhance their visibility in this picture. This visible light image looks toward the unlit side of the rings from below the ringplane.

Image Credit: NASA

Moons at Work


moons_at_workSaturns rings are divided into distinct bands. The Saturnian moons Prometheus and Pan are both caught “shepherding” their respective rings in this image (click the image to embiggen it). Through their gravitational effect on nearby ring particles, one moon maintains a gap in the outer A ring, and the other helps keep another ring narrowly confined.

Prometheus (86 km across) and its partner Pandora (not seen here), maintains the narrow F ring seen at the bottom left in this image. Pan (28 km across) clears the Encke gap in as it moves along the gap’s center. The other bright dot near the inner edge of the Encke gap is a star in the background.

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