apoapse

During its 14.7-hour orbit of Saturn, Prometheus 102 kilometers, or 63 miles across reaches the point in its elliptical path, called apoapse, where it is farthest away from Saturn and closest to the F ring, and the moon's gravity is just strong enough to draw a "streamer" of material out of the core region of the F ring.

Amazing Ring Ripples | Universe Today 2009

The creation of such streamers and channels occurs in a cycle that repeats each Prometheus orbit: when Prometheus again reaches apoapse, it draws another streamer of material from the F ring.

Amazing Ring Ripples | Universe Today 2009

At apoapse, the moon's gravity pulls out particles of the ring into a streamer.

FAZED 2009

The darkest streamer-channel stretching from the top right to the center of the image shows Prometheus 'previous apoapse passage about 15 hours earlier.

FAZED 2009

Then, as Prometheus moves back toward apoapse, the streamer breaks apart which results in a dark channel.

FAZED 2009

Prometheus (86 km / 53 mi across) dips into the inner edge of the F ring when it reaches apoapse, its farthest point from Saturn.

FAZED 2009

Prometheus (86 km / 53 mi across) dips into the inner edge of the F ring when it reaches apoapse, its farthest point from Saturn.

FAZED 2009

Then, as Prometheus moves back toward apoapse, the streamer breaks apart which results in a dark channel.

FAZED 2009

The darkest streamer-channel stretching from the top right to the center of the image shows Prometheus 'previous apoapse passage about 15 hours earlier.

FAZED 2009

At apoapse, the moon's gravity pulls out particles of the ring into a streamer.

FAZED 2009