Saturn's rings

Saturn's rings

Jupiter, Neptune and Uranus have faint rings but they don't compare to Saturn's beautiful ring system.

The rings are about 270,000km in diameter but relatively thin - a maximum thickness of 1km, according to NASA, means that they are difficult to see when viewed edge on from the Earth.

Each ring is composed of many ringlets of ice particles, which vary from dust-sized to 3m or more in diameter. Some of Saturn's small moons such as Prometheus appear to keep the rings in place and are known as shepherd moons.

Photo: Saturn backlit by the Sun taken by the Cassini probe (NASA/JPL/Space Science Institute)

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Saturn's rings

About Saturn's rings

Countless ice particles around Saturn create stunning rings.

About Saturn's rings

The rings of Saturn are the most extensive planetary ring system of any planet in the Solar System. They consist of countless small particles, ranging in size from micrometres to metres, that orbit about Saturn. The ring particles are made almost entirely of water ice, with a trace component of rocky material. There is still no consensus as to their mechanism of formation; some features of the rings suggest a relatively recent origin, but theoretical models indicate they are likely to have formed early in the Solar System's history.

Although reflection from the rings increases Saturn's brightness, they are not visible from Earth with unaided vision. In 1610, the year after Galileo Galilei first turned a telescope to the sky, he became the very first person to observe Saturn's rings, though he could not see them well enough to discern their true nature. In 1655, Christiaan Huygens was the first person to describe them as a disk surrounding Saturn. Although many people think of Saturn's rings as being made up of a series of tiny ringlets (a concept that goes back to Laplace), true gaps are few. It is more correct to think of the rings as an annular disk with concentric local maxima and minima in density and brightness. On the scale of the clumps within the rings there is much empty space.

The rings have numerous gaps where particle density drops sharply: two opened by known moons embedded within them, and many others at locations of known destabilizing orbital resonances with Saturn's moons. Other gaps remain unexplained. Stabilizing resonances, on the other hand, are responsible for the longevity of several rings, such as the Titan Ringlet and the G Ring.

Well beyond the main rings is the Phoebe ring, which is tilted at an angle of 27 degrees to the other rings and, like Phoebe, orbits in retrograde fashion.

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