Two shepherding moons continue to affect Saturn’s F ring in this amazing image captured by Cassini. Pandora on the outside of the ring and Prometheus on the inside, periodically create what are called “streamer-channels,” seen here in the F ring. The potato-shaped Prometheus pulls a streamer of material from the ring and leaves behind a dark channel. During its 14.7-hour orbit of Saturn, Prometheus (102 kilometers, or 63 miles across) reaches the point in its elliptical path, called apoapse, where it is farthest away from Saturn and closest to the F ring, and the moon’s gravity is just strong enough to draw a “streamer” of material out of the core region of the F ring.
The creation of such streamers and channels occurs in a cycle that repeats each Prometheus orbit: when Prometheus again reaches apoapse, it draws another streamer of material from the F ring. But since Prometheus orbits faster than the material in the ring, this new streamer is pulled from a different location in the ring about 3.2 degrees (in longitude) ahead of the previous one.
In this way, a whole series of streamer-channels is created along the F ring. In some observations, 10 to 15 streamer-channels can easily be seen in the F ring at one time.
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This view looks toward the northern, sunlit side of the rings from about 10 degrees above the ringplane.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 20, 2009. The view was obtained at a distance of approximately 2.3 million kilometers (1.4 million miles) from Saturn. Image scale is 13 kilometers (8 miles) per pixel.