Scientists using NASA's Spitzer Space Telescope have discovered that there is an enormous ring outside of all of the other rings around Saturn. The ring is composed of widely diffused particles of dust and ice. The orbital Spitzer telescope, which "sees" in infrared, enabled scientists to spot the glow of the cooler dust against the warmer matter surrounding it. The ring really is absolutely ginormous; astronomer Anne Verbiscer from the University of Virginia, Charlottesville compares it to the size of Earth's moon. "If you could see the ring, it would span the width of two full moons' worth of sky, one on either side of Saturn." Verbiscer and her colleague at the University of Charlottesville, Michael Skrutskie are co-authors of a paper in the journal Nature.

In February of this year, under the theory that there might be a much larger, broader and more diffuse ring outside of the known rings and most of Saturns moons, the astronomers used the Spitzer's ability to see in multiple bandwidths to scan regions near one of Saturn's most distant moons, Phoebe. The ring, formed by accreting material from its surroundings, is 3.7 million miles away from Saturn, and is sharply tilted. The ring extends out another 7.4 million miles, encompassing Saturn's moon Phoebe. Phoebe's entire orbit is within the ring, and is more than likely the source of the material that forms the ring; material ejected for several thousand years. The discovery of the extra-large ring may also help to explain some of the anomalies associated with Iapetus, another of Saturn's many moons. Iapetus has a strikingly noticeable bright side and a dark side; something that Giovanni Cassini spotted in 1671. The giant ring is circling in the same direction as Phoebe, while Iapetus and most of Saturn's other moons are circling in the opposite direction. The dark side, named Cassini Regio in a nod at the astronomer, may have been created by material from the ring being drawn inward towards Iapetus, and smacking into the moon's icy surface, thus rendering that half darker.

I've linked to an artists' representation of the ring in the image above; click it for a larger view. NASA's official press release is here; there's a good discussion of the discovery here at CNN, and more astronomical discussion here. The Nature article "Saturn's Largest Ring" by Anne J. Verbiscer1, Michael F. Skrutskie and Douglas P. Hamilton is here, complete with charts and detailed analysis of the Spitzer telescope data.