The Huygens Gap
The sharp outer boundary of Saturn's B ring, which is the bright ring region seen to the right in this image, is maintained by a strong resonance with the moon Mimas. For every two orbits made by particles at this distance from Saturn, Mimas makes one orbit. The moon's repeated gravitational tugs force ring particles away from this region.
The dark region is called the Huygens gap and it includes the bright, eccentric Huygens ringlet, also visible here near center.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 23, 2006. The view was obtained from 15 degrees beneath the ringplane and at a distance of approximately 282,000 kilometers (175,000 miles) from Saturn. Image scale is 1 kilometer (0.6 mile) per pixel.