A shepherd moon can do more to define ring structures than just keep the
flock of particles in line, as Cassini spacecraft images such as this have
shown.
Prometheus (102 kilometers, or 63 miles across) is seen here with two long
streamers of material that it has pulled out of the F ring. When
Prometheus comes close to the F ring in its orbit, the moon's gravity tugs
on the ring particles. The disturbed particles, now pulled into orbits
slightly closer to Saturn and therefore faster, shear out during
successive orbits, creating the long and delicate streamers seen here.
This view looks toward the unlit side of the rings from about 31 degrees
above the ringplane.
The image was taken in visible light with the Cassini spacecraft
narrow-angle camera on Sept. 29, 2006 at a distance of approximately 1.7
million kilometers (1 million miles) from Prometheus and at a
Sun-Prometheus-spacecraft, or phase, angle of 160 degrees. Image scale is
10 kilometers (6 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/home/index.cfm. The Cassini imaging team
homepage is at http://ciclops.org.