CICLOPS: Cassini Imaging Central Laboratory for OPerationS
Roche Division Shadow Caster

Roche Division Shadow Caster
PIA 11566

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  The moon Prometheus casts a shadow on Saturn's F ring near a streamer-channel it has created on the ring in this image taken as the planet approached its August 2009 equinox.

Prometheus (86 kilometers, 53 miles across) and Atlas (30 kilometers, 19 miles across) both orbit in the Roche Division between the A ring and the thin F ring. Atlas is the smaller moon to the lower left of Prometheus in the image. Other small, bright specks are background stars.

The gravity of potato-shaped Prometheus periodically creates streamer-channels in the F ring. To learn more and to watch a movie of this process, see PIA08397.

The novel illumination geometry created around the time of Saturn's August 2009 equinox allows moons orbiting in or near the plane of Saturn's equatorial rings to cast shadows onto the rings. These scenes are possible only during the few months before and after Saturn's equinox which occurs only once in about 15 Earth years. To learn more about this special time and to see movies of moons' shadows moving across the rings, see PIA11651 and PIA11660.

This view looks toward the unilluminated side of the rings from about 47 degrees above the ringplane.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on June 30, 2009. The view was acquired at a distance of approximately 1.9 million kilometers (1.2 million miles) from Atlas and at a Sun-Atlas-spacecraft, or phase, angle of 88 degrees. Image scale is 11 kilometers (7 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: August 26, 2009 (PIA 11566)
Image/Caption Information

Alliance Member Comments
Dragon_of_Luck_Mah_Jonng1971 (Sep 3, 2009 at 4:48 PM):
A special and interesting view.
mipsandbips (Aug 30, 2009 at 9:15 PM):
The point of impact with the F ring of Prometheus is moving away
from the point of impact as the ring material is deflected towards
its motion. There also appears a very suble reflected shadow at the point
of impact! If this is true then this may have been the first time Cassini has
captured one orbiting object casting 2 shadows in the same image!!