Busy Moon

Half an hour after Prometheus tore into Saturn's F ring, Cassini snapped this image just as the moon was creating a new streamer in the ring. The dark pattern shaped like an upside down check mark in the lower left of the image is Prometheus and its shadow. The potato shaped moon can just be seen coming back out of the ring.

The moon’s handiwork also is apparent in two previous streamer-channel formations on the right of the image. The darkest streamer-channel stretching from the top right to the center of the image shows Prometheus’ previous apoapse passage about 15 hours earlier. A fainter, even earlier channel extends to the edge of the image.

Prometheus (86 kilometers, 53 miles across) dips into the inner edge of the F ring when it reaches apoapse, its farthest point from Saturn. At apoapse, the moon’s gravity pulls out particles of the ring into a streamer. As Prometheus moves back toward periapse -- its orbit's closest point to the planet -- the streamer gets longer. Then, as Prometheus moves back toward apoapse, the streamer breaks apart which results in a dark channel. This streamer-channel cycle repeats once every orbit with the streamer-channel features being streamers during Prometheus periapse and channels during Prometheus apoapse.

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