CICLOPS: Cassini Imaging Central Laboratory for OPerationS
The Prometheus Effect

The Prometheus Effect
PIA 07750

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  This mosaic of 15 Cassini images of the F ring shows how Prometheus creates a gore in the ring once every 14.7 hours as it approaches and recedes from the F ring on its eccentric orbit.

The individual images have been processed to make the ring appear as if it has been straightened, making it easier to see the ring's structure. The mosaic shows a region 147,000 kilometers (91,000 miles) along the ring (horizontal direction in the image); this represents about 60 degrees of longitude around the ring. The region seen here is about 1,500 kilometers (900 miles) across (vertical direction). The first and last images in the mosaic were taken approximately 2.5 hours apart.

Each dark channel, or "gore", is clearly visible across more than 1,000 kilometers (600 miles) of the ring and is due to the gravitational effect of Prometheus (86 kilometers, 53 miles across), even though the moon does not enter the F ring. The channels have different tilts because the ring particles closer to Prometheus (overexposed, stretched, and just visible at the bottom right of the image) move slower with respect to the moon than those farther away. This causes the channels to shear with time, their slopes becoming greater, and gives the overall visual impression of drapes of ring material. The channels at right are the youngest and have near-vertical slopes while those at the left are the oldest and have near-horizontal slopes.

This phenomenon has not previously been detected in any other planetary ring system, but computer simulations of the system prove that the disturbance is caused by a simple gravitational interaction. Prometheus' eccentric orbit is at present gradually moving so that the moon will eventually come even closer in its closest approach to the eccentric F ring, and scientists calculate that its perturbations of the F ring will reach a maximum in December 2009.

The images in this mosaic were taken using the narrow angle camera on April 13, 2005 from a distance of approximately 1.1 million kilometers (700,000 miles) from Saturn. The resolution in the original images, before reprojection, was 6 kilometers (4 miles) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. 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-Huygens mission, visit and the Cassini imaging team home page,

Credit: NASA/JPL/Space Science Institute/Queen Mary, University of London
Released: October 26, 2005 (PIA 07750)
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