Prometheus shines brightly in this image, taken as part of the ongoing
campaign to precisely determine the orbits of Saturn's small moons.
Moons are usually quite bright in this type of observation, due to the
long exposure times employed. Long exposures are required in order to
gather enough light so that dim, 12th (or even 13th or 14th) magnitude
stars are visible in the background, making it possible to determine where
the Cassini spacecraft is pointed on the sky with great accuracy. Imaging
scientists are then able to precisely determine the position of the moon's
center, thus refining their understanding of the moon's orbit and any
changes to it over time due to perturbations by other moons.
Two stars can be seen in this view: one to the right of Prometheus and one
near lower left.
Exterior to Prometheus (102 kilometers, or 63 miles across) is the F ring,
with its inner and outer flanking ringlets and a streamer channel created
by the moon. The outer A ring is seen at top.
This view looks toward the unilluminated side of the rings from about 21
degrees above the ringplane. The image was taken in visible light with the
Cassini spacecraft narrow-angle camera on Jan. 22, 2008. The view was
obtained at a distance of approximately 1.7 million kilometers (1.1
million miles) from Prometheus and at a Sun-Prometheus-spacecraft, or
phase, angle of 34 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.
