Saturn's ring rhythm

On 3 May 2005, for an Earth observer, the Cassini spacecraft appeared to pass behind the rings, then Saturn, then the rings again (the red line). A harmonic structure was discovered both, on the way in and out, but only in locations where icy particles are densely packed together, such as the B-ring and the innermost part of the A-ring.

A radio experiment performed by Cassini on 3 May and several others that followed in 2005 showed that the regular spacing of the harmonic structure varies from 100 to 250 m, depending on the location in the rings.