Saturn’s biggest ring is out of hiding

Saturn is famous for the spectacular collection of rings that encircle it. But the biggest has gone completely unnoticed – until now. That is because the band of cool dust and ice particles is too faint to be seen in normal light.

It only revealed its presence when the infrared eye of NASA’s Spitzer space telescope was turned on the planet.

Unlike the other thin but bright rings that may be seen in the smallest of telescopes, the new ring is vast – so big, in fact, that you could fit a billion Earths inside it.

It is 20 times thicker than gas giant Saturn is wide. And the new band’s own width is around 12 million km (7.4 million miles).

It is also tilted at and angle of 27° to the other rings and lies far beyond them – the inner edge only begins about 6 million km (3.7 million miles) from the planet.

Astronomer Anne Verbiscer, of the University of Virginia, said: “This is one supersized ring. If you could see the ring, it would span the width of two full moons’ worth of sky, one on either side of Saturn.”

One of Saturn’s most distant moons, 230km-wide Phoebe, orbits the planet within the new ring. Its impacts with asteroids are thought to have supplied the dust that formed it.

The new ring may also solve a long-standing mystery concerning another of Saturn’s moons, Iapetus. The 1,500km-wide satellite has one side much darker than the other, making it vary in brightness by two magnitudes.

Scientists say that this dark side, named Cassini Regio after the moon’s 17th-century discoverer Giovanni Cassini, is caused by a stream of dust from the new ring hitting it like flies slamming into a car’s windscreen.

Its discovery is revealed this week in the journal Nature.

A co-discoverer of the new ring, Douglas Hamilton of the University of Maryland, said: “Astronomers have long suspected that there is a connection between Saturn’s outer moon Phoebe and the dark material on Iapetus. This new ring provides convincing evidence of that relationship.”

A spaceprobe, also named after Cassini, is currently orbiting Saturn and returning a host of great findings about the planet and its many moons and rings.

The ring discovery is just the latest triumph for the Spitzer space telescope which has also detected a cosmic collision, newly forming solar systems and hints that Star Trek Spock’s planet Vulcan could really exist.

Pictures: The images show an impression of the enormous new ring and a labelled explanation of its layout. (NASA).