CICLOPS: Cassini Imaging Central Laboratory for OPerationS
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.

The F ring is overexposed in this image which has been brightened to reveal the moon.

This view looks toward the unilluminated side of the rings from about 18 degrees above the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 14, 2009. The view was obtained at a distance of approximately 555,000 kilometers (345,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 145 degrees. Image scale is 3 kilometers (2 miles) per pixel.

The Cassini Equinox Mission is a joint United States and European endeavor. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini Equinox Mission visit, and

Credit: NASA/JPL/Space Science Institute
Released: March 6, 2009 (PIA 10593)
Image/Caption Information
  Busy Moon
PIA 10593

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Alliance Member Comments
Harry (Mar 6, 2009 at 2:53 PM):
With Prometheus converging on the ring, I presume some of the ring material is accumulating on the surface. I wonder if larger or smaller particles stay attached to Prometheus? Wouldn't it be great to have a shovel full for a quick analysis in JSC's lunar dirt lab?
Dragon_of_Luck_Mah_Jonng1971 (Mar 6, 2009 at 2:18 PM):
A small moon but with a very strong influence on the F ring and its surroundings. If Prometheus were not at its place then the inner area adjacent to the F ring would be many more "tidied up" , without those streamers ( streamer channels ).
Red_dragon (Mar 6, 2009 at 8:13 AM):
You know, images as this one show you don't need to make a color one to impress us. The things gravity can do -even accounting for the small mass of Prometheus- are impressive.