Saturn - Rings - UNIVERSE

The rings of Saturn have puzzled astronomers since Galileo Galilei discovered them with his telescope in 1610. Detailed study by the Voyager 1 and Voyager 2 spacecraft in the 1980s only increased the mystery.

There are billions of ring particles in the entire ring system. The ring particle sizes range from tiny, dust-sized icy grains to a few particles as large as mountains. Two tiny moons orbit in gaps (Encke and Keeler gaps) in the rings and keep the gaps open. Other particles (10s to 100s of meters) are too tiny to see, but create propeller-shaped objects in the rings that let us know they are there.

The rings are believed to be pieces of comets, asteroids or shattered moons that broke up before they reached the planet. Each ring orbits at a different speed around the planet. Information from NASA's Cassini mission will help reveal how they formed, how they maintain their orbit and, above all, why they are there in the first place.

While the other three gas planets in the solar system -- Jupiter, Uranus and Neptune -- have rings orbiting around them, Saturn's are by far the largest and most spectacular. With a thickness of about one kilometer (3,200 feet) or less, they span up to 282,000 km (175,000 miles), about three quarters of the distance between the Earth and its Moon.

Named alphabetically in the order they were discovered, the rings are relatively close to each other, with the exception of the Cassini Division, a gap measuring 4,700 km (2,920 miles). The main rings are, working outward from the planet, known as C, B and A. The Cassini Division is the largest gap in the rings and separates Rings B and A.

The D Ring is exceedingly faint and closest to the planet. The F Ring is a narrow feature just outside the A Ring. Beyond that are two far fainter rings named G and E. The rings show a tremendous amount of structure on all scales; some of this structure is related to gravitational perturbations by Saturn's many moons, but much of it remains unexplained.

To enter Saturn's orbit, Cassini flew through the gap between the F and G rings, which is farther from the planet than the Cassini Division. As a safety measure, during the crossing of the ring plane, instruments and cameras on board the spacecraft were shut off temporarily. However, the spectacular crossing into Saturn's orbit brought incredible information, images and footage. The instruments on board Cassini are still collecting unique data that may answer many questions about the rings' composition.

Reference:http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens/Saturn_s_rings
http://solarsystem.nasa.gov/planets/saturn/rings