Solar System

Rings

11.6 - Understand the following principal characteristics of the planets:
f) presence of ring systems

The gas giants have rings with the most notable being Saturn’s.

Saturn's rings were first noticed, rather than discovered, by Galileo who observed that the planet had two protrusions or two considerable moons.

It was not until later that the rings were discovered by Christian Huygens. Normally they are impressive, however when Saturn is at 90° to Earth the rings are hardly noticeable.

The rings are made of thousands, if not millions of particles orbiting the planet. They are kept in place by Saturn’s gravity and some larger rocks called Sheppard moons. There are several separate rings separated by gaps. The largest gap is called the Cassini Division after the astronomer who first noticed them.

They are still not fully understood. Their origins may be due to a moon coming too near Saturn and being ripped apart by the planet's gravity. The area at which an object may approach a planet is called the Roche limit. They usually orbit the planet at its equator.

The rings of Uranus were first detected when Uranus occulted a star in 1977. Scientists detected blips of darkness from the occulted star before and after Uranus passed in front of it suggesting Uranus had a series of thin rings surrounding it. They were easier to detect because they were facing Earth, so they looked circular rather than as a flattened ellipse because Uranus orbits the Sun on its side.

Both the other gas giants, Jupiter and Neptune also have rings surrounding them. They were discovered by the voyager probes. These rings are very thin and made of dark material and not noticeable from Earth.