PIA11144: 'Tis the Season for Spokes
- Original Caption Released with Image:
Click on the image for the movie
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).
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.
- Image Credit:
NASA/JPL/Space Science Institute