Cassini Mission Update:
Larry Esposito—This mosaic of 15 Cassini images of the F ring shows how Prometheus creates a gore (dark channel) in the ring once every 14.7 hours as it approaches and recedes from the F ring on its eccentric orbit. The individual images have been processed to make the ring appear as if it has been straightened, making it easier to see the ring’s structure. The mosaic shows a region 147,000 kilometers (91,000 miles) along the ring (horizontal direction in the image); this represents about 60 degrees of longitude around the ring. The region seen here is about 1,500 kilometers (900 miles) across (vertical direction). The first and last images in the mosaic were taken approximately 2.5 hours apart. Each dark channel, or “gore”, is clearly visible across more than 1,000 kilometers (600 miles) of the ring and is due to the gravitational effect of Prometheus (102 kilometers, 63 miles across), even though the moon does not enter the F ring. The channels have different tilts because the ring particles closer to Prometheus (overexposed, stretched, and just visible at the bottom right of the image) move slower with respect to the moon than those farther away. This causes the channels to shear with time, their slopes becoming greater, and gives the overall visual impression of drapes of ring material. The channels at right are the youngest and have near-vertical slopes while those at the left are the oldest and have near-horizontal slopes.