Saturn's moon Pan is seen here orbiting within the Encke Gap in Saturn's A
ring in two differently processed versions of the same Cassini image. The
little moon is responsible for clearing and maintaining this gap, named
for Johann Franz Encke, who discovered it in 1837. Pan is 20 kilometers
(12 miles) across.
The top image reveals two of the faint, dusty ringlets that occupy the
gap along with Pan. One of the ringlets occupies nearly the same orbit as
Pan, while the other is closer to the gap's inner edge. Not only do the
ringlets vary in brightness, but they also appear to move in and out along
their length, resulting in notable "kinks," which are similar in
appearance to those observed in the F ring (see PIA06585). One possible
explanation for the complex structure of the ringlets is that Pan may not
be the only moonlet in this gap.
Pan is responsible for creating stripes, called 'wakes,' in the ring
material on either side of it. Since ring particles closer to Saturn than
Pan move faster in their orbits, these particles pass the moon and receive
a gravitational "kick" from Pan as they do. This kick causes waves to
develop in the gap where the particles have recently interacted with Pan
(see PIA06099), and also throughout the
ring, extending hundreds of kilometers into the rings. These waves
intersect downstream to create the wakes, places where ring material has
bunched up in an orderly manner thanks to Pan's gravitational kick.
In the bottom image, the bright stripes or wakes moving diagonally away
from the gap's edges can be easily seen. The particles near the inner gap
edge have most recently interacted with Pan and have just passed the moon.
Because of this, the disturbances caused by Pan on the inner gap edge are
ahead of the moon. The reverse is true at the outer edge: the particles
have just been overtaken by Pan, leaving the wakes behind it.
This image was taken in visible light with the Cassini spacecraft
narrow-angle camera on May 18, 2005, at a distance of approximately 1.6
million kilometers (1 million miles) from Pan and at a Sun-Pan-spacecraft,
or phase, angle of 44 degrees. The image scale is 9 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 team is based at the Space Science
Institute, Boulder, Colo.
For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov.
For additional images visit the Cassini imaging team homepage http://ciclops.org.