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 C 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 C Ring was the third ring of Saturn's ring system to be discovered and as shown in the above photos, is the closest of the three main rings. It is fainter than both the B Ring and the A Ring, and is between the B ring (25,500 km) and the A ring (14,600 km) in width at 17,500 km. It was first discovered by William and George Bond in 1850, though William R. Dawes and Johann Galle also independently saw it. William Lassell nicknamed the ring, "Crepe Ring" as it is darker than the A Ring and the B Ring, and to him, resembled the black cloth associated with funerals.

 

It is only five meters thick from top to bottom, and even though it is dark, it is relatively transparent. Between 5% to 12% of light incident on it well be blocked, so it is very easy to see though. It is composed of boulder-sized ice chunks, while the A Ring and B Ring are golf ball sized and smaller. Even though it is made up of ice, it is still darker, meaning that the ice may be covered with a crust of dust, prevently light from being reflected efficiently.

 

The C Ring has smaller parts to it, including the Colombo Gap and Titan Ringlet, the Maxwell Gap and Maxwell Ringlet, the Bond Gap, 1.470 Rs Ringlet, 1.495 Rs Ringlet, and the Dawes Gap. The Titan Ringlet is unique in that it shares a resonance with Titan, so that Titan somewhat controls the rotation of the Ringlet. The Maxwell Gap and Ringlet are named after James Clerk Maxwell, who had mathematically calculated that the rings could not be solid disks, the Bond Gap named after William and George Bond, and the Dawes Gap is named after William R. Dawes.