CICLOPS: Cassini Imaging Central Laboratory for OPerationS
Saturn's Watch Spiral

Spiral density waves in Saturn's A ring reveal the gravitational signatures of distant moons as they subtly tug on the countless particles orbiting in the ring plane.

A spiral density wave is a spiral-shaped massing of particles that tightly winds many times around the planet. Thus, the wave patterns seen here represent successive windings of each wave, like a closeup view of a watch spring.

Ring scientists can read these patterns, learning from them how quickly the rings are spreading and the amount of mass contained in a region.

This view looks toward the sunlit side of the rings from about 42 degrees below the ringplane.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on April 1, 2008. The view was obtained at a distance of approximately 268,000 kilometers (167,000 miles) from Saturn. Image scale is 1 kilometer (0.6 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 Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission, visit and the Cassini imaging team home page,

Credit: NASA/JPL/Space Science Institute
Released: May 5, 2008 (PIA 09894)
Image/Caption Information
  Saturn's Watch Spiral
PIA 09894

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Alliance Member Comments
gandalf (May 25, 2008 at 10:44 AM):
As the universe formed after the Big Bang,it didn't form in an even distibution as COBE and WMAP have shown from the microwave background radiation. This uneven or clumpy composition could inherently cause angular momentum.
More to the point...fantastic views of the ring system. Well done CICLOPS !!!
Tiger (May 24, 2008 at 4:19 PM):
nekto,I think the answer to your question is... the angular momentum comes from the shock waves of the big bang.
Tiger (May 24, 2008 at 4:16 PM):
do you have an idea about how saturn`s rings were formed carolyn?
NeKto (May 23, 2008 at 1:23 PM):
I recall reading something 40 or so years ago that stated that all the angular momentum in the universe HAD to add up to zero. (Rather dogmatic i think.) Your team's work at Saturn has shown that some of the most breathtaking views in the universe have angular momentum as a primary component. The big orb with the big rings sure does make spin look good!
carolyn (CICLOPS) (May 13, 2008 at 2:11 PM):
It could be that averaged over the entire Universe, which was of course very small at the very beginning, there is no spin. Spin may just be a result of the statistical fluctuations in the motions of bits of matter relative to each other. But I am not that fluent in the work of Hawking to state what he has to say on this matter. The above is just my own conjecture.
NeKto (May 13, 2008 at 12:53 PM):
Carolyn, You gave one excelent, and clasic, example of the conservation of angular momentum. I'm stil wondering where the primordial angular momentum came from. Has Stephen Haking said anything about the rotation of the big bang?
carolyn (CICLOPS) (May 11, 2008 at 3:54 PM):
Most cosmic entities -- like the giant clouds of gas that galaxies formed from or the molecular clouds that stellar systems (and their planets) form from -- start with some amount of spin. The gravitational contraction process makes them spin even faster, in a similar manner to the way an ice skater will spin faster if she brings her arms in closer to her body.
NeKto (May 9, 2008 at 2:48 PM):
It seams the most common things we see in the universe are either rotating discs or rotating spheroids. Has anyone found an answer for where the angular momentum came from?
Red_dragon (May 9, 2008 at 7:21 AM):
Thanks; i was suspecting the difference was precissely the great difference in the mass distribution between a galaxy and Saturn's ring system.
Anyway, it's beautiful to see similar physical processes working at scales so different as planetary ones and galactic ones.
carolyn (CICLOPS) (May 6, 2008 at 1:37 PM):
The physics is almost identical. The big difference is that in a spiral galaxy, the mass is distributed more or less evenly across the disk, making for a spiral arm with a big wavelength (ie, big separation from one winding to the other). In Saturn's rings, the vast bulk of the mass in the dynamical system is in the planet itself, with very little mass in the disk, and this makes for a much tighter winding.

This is why we can learn about disk systems throughout the cosmos -- regardless of size -- by studying the processes ongoing in Saturn's rings.
Red_dragon (May 6, 2008 at 3:23 AM):
Just one question: are those "spiral waves" the same that are responsable for shaping spiral galaxies?
alwolfe (May 5, 2008 at 1:42 PM):
Lovely visualization of the "music of the spheres." I look forward to seeing the published paper.
carolyn (CICLOPS) (May 5, 2008 at 9:42 AM):
alwolfe: We are presently writing a paper cataloguing all the resonances which are visible in our images. It will be a while before we finish it and get it published.
alwolfe (May 5, 2008 at 9:26 AM):
Which resonances are behind the waves in this image?
Red_dragon (May 5, 2008 at 7:07 AM):
The patterns nature can create are nothing less than breathtaking and this image shows it quite well.