One of several tiny “shepherd” moons, a well-lit Prometheus cruises the gap between Saturn’s A and F rings, clearing the channel while pulling up a small plume of material from the ropy F ring as it passes by.
This is from raw image data shot by Cassini on February 10, 2009. I adjusted the image to enhance detail and increase contrast, and I also added a slight beige tint to the A ring. Stars were also visible in the background.
Shepherd moons are so called because their orbits within the ring system clear pathways and keep the icy particles in adjacent rings in their places. Occasionally their tumbling orbits come close to the rings, stirring up material in their wake with their gravity. This material, bits of dust and ice most no larger than sand grains, eventually falls back into place. Click here for a video of the effect.
The irregularly-shaped Prometheus is about 63 miles across.
Image credit: NASA/JPL/Space Science Institute