关于这张图
Seen by NASA Cassini spacecraft within the vast expanse of Saturn rings, Prometheus appears as little more than a dot. But that little moon still manages to shape the F ring, confining it to its narrow domain. Prometheus (53 miles, or 86 kilometers across) and its fellow moon Pandora (50 miles, or 81 kilometers across) orbit beside the F ring and keep the ring from spreading outward through a process dubbed "shepherding." This view looks toward the unilluminated side of the rings from about 45 degrees below the ringplane. The image was taken in green light with the Cassini spacecraft wide-an…
