CICLOPS: Cassini Imaging Central Laboratory for OPerationS
Prometheus and Pan Pair

Prometheus and Pan Pair
PIA 11604

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  Saturn's moons Prometheus and Pan cast a pair of shadows on the A ring in this image taken shortly after the planet's August 2009 equinox.

Pan (28 kilometers, 17 miles across) orbits in the Encke Gap of the A ring, and it can be seen casting a shadow to the right of and a little below Prometheus' shadow in this image.

The gravity of potato-shaped Prometheus (86 kilometers, 53 miles across) periodically creates streamer-channels in the F ring, and the moon's handiwork can be seen above the moon in this image. To learn more and to watch a movie of this process, see PIA08397.

Kinky, discontinuous ringlets in the Encke Gap are also visible at the bottom of the image. See PIA11676 to learn more.

The novel illumination geometry that accompanies equinox lowers the sun's angle to the ringplane, significantly darkens the rings, and causes out-of-plane structures to look anomalously bright and cast shadows across 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. Before and after equinox, Cassini's cameras have spotted not only the predictable shadows of some of Saturn's moons (see PIA11657), but also the shadows of newly revealed vertical structures in the rings themselves (see PIA11665).

This view looks toward the northern, sunlit side of the rings from about 8 degrees above the ringplane. The main rings have been brightened relative to the F-ring to increase visibility.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 21, 2009. The view was acquired at a distance of approximately 2.2 million kilometers (1.4 million miles) from Saturn. Image scale is 13 kilometers (8 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: October 19, 2009 (PIA 11604)
Image/Caption Information

Alliance Member Comments
mipsandbips (Oct 19, 2009 at 6:59 PM):
Thank you again Ciclops!! In image PIA11676, (Shadows and More Shadows)
the kinks in the Encke Gap had shown a distinct height by their
shadows but Pan was not visibile in that magnification of the image.
Here, however, Pan is clearly visible and and in relation to the shadow
heights onto the A ring from the inner material band, Pan is clearly leading
the wake of the inner band by a considerable distance when compared to Daphne's
wake in the Keeler Gap where the wake is see on either side of its orbit.
The leads one to speculate as to whether vibrations in the inner band
material of the Encke Gap causes oscillations in the middle band which
then causes the shadows to appear onto the inner A rimg.