This collection of Cassini images provides context for understanding the
location and scale of propeller-shaped features observed within Saturn's A
ring.
Careful analysis of the highest resolution images taken by Cassini's
cameras as the spacecraft slipped into Saturn orbit revealed the four
faint, propeller-shaped double-streaks in an otherwise bland part of the
mid-A ring. Imaging scientists believe the "propellers" provide the first
direct observation of the dynamical effects of moonlets approximately 100
meters (300 feet) in diameter. The propeller moonlets represent a hitherto
unseen size-class of particles orbiting within the rings.
The left-hand panel provides broad context within the rings, and shows the
B ring, Cassini Division, A ring and F ring. Image scale in the radial, or
outward from Saturn, direction is about 45 kilometers (28 miles) per
pixel; because the rings are viewed at an angle, the image scale in the
longitudinal, or circumferential, direction is several times greater.
The center image is a closer view of the A ring, showing the radial
locations where propeller features were spotted. The view is approximately
1,800 kilometers (1,100 miles) across from top to bottom and includes a
large density wave at bottom (caused by the moons Janus and Epimetheus),
as well as two smaller density waves. The footprints of the propeller
discovery images are between density waves, in bland, quiescent regions of
the ring.
The propellers appear as double dashes in the two close-up discovery
images at the right and are circled. The unseen moonlets, each roughly
the size of a football field, lie in the center of each structure. These
two images were taken during Saturn orbit insertion on July 1, 2004, and
are presented here at one-half scale. Resolution in the original images
was 52 meters (171 feet) per pixel. The horizontal lines in the image
represent electronic noise and do not correspond to ring features.
The propellers are about 5 kilometers (3 miles) long from tip to tip, and
the radial offset (the "leading" dash is slightly closer to Saturn) is
about 300 meters (1,000 feet).
The propeller structures are unchanged as they orbit the planet. In that
way, they are much like the wave pattern that trails after a speedboat as
it skims across a smooth lake. Such a pattern is hard to discern in a
choppy sea. In much the same way, scientists think other effects may be
preventing Cassini from seeing the propellers except in very bland parts
of the rings.
See PIA07790 and PIA07791 for additional images showing these features.
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.