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.