This mosaic of 15 Cassini images of Saturn's F ring shows how the moon
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 (102 kilometers, or 63 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 the right are the youngest and
have near-vertical slopes, while those at the left are the oldest and have
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. The eccentric
orbit of Prometheus is gradually moving so that the moon will eventually
come even closer in its closest approach to the eccentric F ring.
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 Cassini spacecraft
narrow-angle camera on April 13, 2005, at 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 mission for NASA's Science Mission Directorate, Washington, D.C. The
Cassini orbiter and its two onboard cameras were designed, developed and
assembled at JPL. The imaging operations center is based at the Space
Science Institute in Boulder, Colo.
For more information about the Cassini-Huygens mission visit
http://saturn.jpl.nasa.gov. The Cassini imaging team homepage is at