Saturn's moon Prometheus casts a shadow on the narrow F ring in this image
captured weeks after the planet's August 2009 equinox.
The gravity of potato-shaped Prometheus (86 kilometers, or 53 miles
across) periodically creates streamer-channels in the F ring, and the
moon's handiwork can be seen to the right of the shadow. To learn more and
to watch a movie of this process, see PIA08397.
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 sunlit, northern side of the rings from about
11 degrees above the ringplane. Prometheus was overexposed in this image
and has been dimmed by a factor of three.
The image was taken in visible light with the Cassini spacecraft
narrow-angle camera on Sept. 23, 2009. The view was acquired at a distance
of approximately 2 million kilometers (1.2 million miles) from Prometheus
and at a Sun-Prometheus-spacecraft, or phase, angle of 74 degrees. Image
scale is 12 kilometers (7 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 http://ciclops.org.
