CICLOPS: Cassini Imaging Central Laboratory for OPerationS
Complex Edge Waves

Waves in the edges of the Keeler gap in Saturn's A ring, created by the embedded moon Daphnis, show considerable complexity in this image taken as Saturn approached its August 2009 equinox.

Daphnis (8 kilometers, 5 miles across) orbits in the A ring's Keeler Gap. Equinox has exposed shadows cast by edge waves, or vertical structures of ring material created by Daphnis' gravity (see PIA11655). The low sun illumination angle, and the resulting shadows, have revealed a complexity in these features not seen before.

The novel illumination geometry created around the time of Saturn's August 2009 equinox allows out-of-plane structures and 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 24 degrees above the ringplane.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 11, 2009. The view was acquired at a distance of approximately 496,000 kilometers (308,000 miles) from Daphnis and at a Sun-Daphnis-spacecraft, or phase, angle of 27 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: September 2, 2009 (PIA 11571)
Image/Caption Information
  Complex Edge Waves
PIA 11571

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Alliance Member Comments
Harry (Sep 16, 2009 at 5:10 PM):
So very COOL! Wouldn't it be interesting to actually stand on Daphnis and see this "gravitational drag" in person?... This would make a great scene in Star Trek although it would probably be so bizarre as to confound the audience.
pygar (Sep 15, 2009 at 12:35 PM):
Thank you for your explanation of the gravity waves. The more I learn from the images you have posted the more I am in awe of the nature of the universe. You truely have a great opportunity to work with this data. It's art and science all in one.
carolyn (CICLOPS) (Sep 8, 2009 at 8:00 AM):
Voyager6: Because the particles are highly inelastic and lose a lot of their excess energy when they collide. So wave motions will damp out eventually.
Jay55 (Sep 8, 2009 at 6:58 AM):
its amazing how the particles flatten back out so quickly. Why is that?
carolyn (CICLOPS) (Sep 5, 2009 at 9:04 AM):
pygar: All the bodies in the rings -- ring particles and embedded moons -- travel at the speed appropriate for their distance from Saturn. The farther from Saturn, the slower they travel. Consequently, if you were sitting on Daphnis, the particles closer to Saturn can overtake and eventually pass the moon and get ahead of it; the ones farther away from Saturn, again seen from Daphnis, pass the moon going in the opposite direction and consequently fall behind. Also, the disturbances that Daphnis generates in the trajectories of the particles take affect *after* the particles pass the moon. Put these two circumstances together and you find that the particles on the inside track (closer to Saturn) exhibit disturbed motion ahead of the moon, and those on the outside track (farther from Saturn) show disturbed motion behind the moon. And that's what we see in the waves generated by Daphnis on the inside and outside edges of the Keeler gap.
pygar (Sep 4, 2009 at 3:00 PM):
I would like to understand why the gravity waves are propogated on both sides of Daphinis. I am not sure if the moonlet is orbiting in synchronicity with the rings or if the rings travel at differing speeds from each other and Daphinis causing the outer and inner ring surfaces to have 'opposing' gravity waves. Any comments that might help?

A fabulous image!
stowaway (Sep 2, 2009 at 12:54 PM):
The best one yet. innnnnn - credible