http://www.planetary.org/blog/article/00002144/ wrote:
The amazing wound-up C ring
by Josh Colwell Oct. 7, 2009
<<Analyzing images taken near equinox, Hedman noticed that the spiral pattern in [Saturn's] D ring continues into, and all the way across, the C ring. The winding pattern of the spiral matches perfectly across the C ring/D ring boundary. Now, instead of a spiral that is a few hundred kilometers wide and potentially due to an unusual impact in the D ring,
there is a spiral that is over 15,000 kilometers from its inner edge to its outer edge!
The amplitude of the tilt in the C ring is much smaller than in the D ring, so it was not visible earlier, like the D ring spiral was. The [precession induced spiraling] timing remains the same: something happened in
1984 that caused Saturn's rings to become tilted relative to Saturn's equator. And this "something" had to have happened within a few weeks, according to Matt Tiscareno, one of the co-authors of this work.
What are the options? Either the rings were tilted, or something inside Saturn responsible for defining its net gravitational equatorial plane tilted. Neither one is something that would seem plausible. Ordinarily.
But the observational evidence here is compelling. Tilting that broad a region of the rings (which are made up of countless small particles) is not easy. I can't think of any way to do that. A large object passing through the ring would not produce the kind of initial tilt that would lead to the very regular spiral pattern across the entire C ring as observed by Cassini.
The alternative, odd as it may seem, is that
something shifted inside Saturn in 1984 that, within a few weeks, caused the net gravitational equatorial plane of the planet to shift from one orientation to another. The rings were then essentially tilted, and the spiral winding began. The mysteries of Saturn's rings will require more observations and some innovative models to untangle.>>
