The Cassini Division

Image Credit: NASA

The Cassini Division is a gap in the ring system of Saturn between the B Ring and the A Ring. It was discovered in 1675 by Giovanni Cassini, hence its name. From Earth, it appears dark and therefore, it was believed that this part of the ring system did not contain any particles. However, when Voyager passed by Saturn, it discovered that there were particles in the division, similar to those in the C Ring. However, they are much more dispersed than in the C Ring, so the division looks empty from Earth.

There are ringlets in the Cassini Division which is caused by resonance with two moons: Mimas which shares a 2:1 resonance with the division (for every one orbit of Mimas, the ringlet makes two) and Enceladus which shares a 3:1 resonance. Mimas and Enceladus tug on the particles in the Cassinin Division, keeping it relatively clear of any particles.

Also, there is a gap in the division called the Huygens Gap. The Huygens Gap contains the ringlet created by the resonance with Mimas.

The B Ring of Saturn

Saturn's rings dark side mosaic

Image Credit:

NASA/JPL/Space Science Institute

Saturn's Ring Plane

Image Credit:

NASA/JPL/Space Science Institute

 

The B Ring is the second ring of Saturn discovered, and the third ring from Saturn. It is composed mostly of golf ball-sized and smaller ice particles, making it very reflective and bright, compared to all the other rings. It is much brighter than the C Ring and the A Ring, and is by far the widest of all the main rings. Because of its width and its depth of 5 to 15 km, it is also the heaviest ring.

 

Unlike the C Ring, which is very transparent, the B Ring blocks 91% of all light incident on it, reflecting most of it, allowing us to see it very easily.

 

Also unlike the C Ring, which has small scale structures inside the ring itself, the B Ring does not contain gaps, but only small ringlets within its structure. The unique feature of the B Ring, however, is the radial lines evident in the rings. These spokes, as they are referred to, are not from gravity, but from Saturn's magnetic field. If the spokes were due to gravity, they would remain in place, even as the planet rotated. But instead, they have a period the same as the magnetic field of Saturn, so we know that they are created by magnetism.

Dark Spokes in the B Ring

Image Credit:

NASA/JPL/Space Science Institute

Rotation of the Spokes

Image Credit:

NASA/JPL/Space Science Institute