PIA11144: 'Tis the Season for Spokes


‘Tis the Season for Spokes

Caption:

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Dark spokes dance around Saturn's B ring in this series of movies comprised of images taken with Cassini's wide-angle camera.

This animation is a concatenation of spoke movies acquired by NASA's Cassini spacecraft in the second half of 2008 on Aug. 21, Sept. 19, Sept. 26, Oct. 11, and Nov. 25.

As Saturn nears equinox in August 2009 and the sun angle on the ring plane decreases, spokes become common sights in Cassini images, just as they were in Voyager images (See PIA02275 ). The planet's orbital period is 29.5 years, so Saturn has nearly made one complete trip around the sun since the flybys of the two Voyager spacecraft in 1980 and 1981, allowing Cassini to closely match Voyager's viewing geometry.

Each of these five movies shows the sunlit side of the rings at low solar phase, or spacecraft-rings-sun, angles. The spokes appear dark against Saturn's B ring at low phase angles because the particles within them scatter light more efficiently in the forward direction (away from Cassini) than the surrounding larger ring particles. In the opposite viewing geometry, at high phase angles, spokes appear bright relative to surrounding ring particles (See PIA07807 ).

Background Info:

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 .

Cataloging Keywords:

Name Value Additional Values
Target Rhea B Ring, Saturn, Saturn Rings
System Saturn
Target Type Satellite Planet, Ring
Mission Cassini-Huygens Voyager
Instrument Host Cassini Orbiter
Host Type Orbiter Flyby Spacecraft
Instrument Imaging Science Subsystem (ISS)
Detector Wide Angle Camera
Extra Keywords Color, Movie, Visual
Acquisition Date
Release Date 2008-12-30
Date in Caption
Image Credit NASA/JPL/Space Science Institute
Source photojournal.jpl.nasa.gov/catalog/PIA11144
Identifier PIA11144