A colossal new ring has been identified around Saturn.
The dusty hoop lies some 13 million km (eight million miles) from the planet, about 50 times more distant than the other rings and in a different plane.
Scientists tell the journal Nature that the tenuous ring is probably made up of debris kicked off Saturn's moon Phoebe by small impacts.
They think this dust then migrates towards the planet where it is picked up by another Saturnian moon, Iapetus.
The discovery would appear to resolve a longstanding mystery in planetary science: why the walnut-shaped Iapetus has a two-tone complexion, with one side of the moon significantly darker than the other.
"It has essentially a head-on collision. The particles smack Iapetus like bugs on a windshield," said Anne Verbiscer from the University of Virginia, US.
Observations of the material coating the dark face of Iapetus indicate it has a similar composition to the surface material on Phoebe.
The scale of the new ring feature is astonishing. Nothing like it has been seen elsewhere in the Solar System.
The more easily visible outlier in Saturn's famous bands of ice and dust is its E-ring, which encompasses the orbit of the moon Enceladus. This circles the planet at a distance of just 240,000km.
The newly identified torus is not only much broader and further out, it is also tilted at an angle of 27 degrees to the plane on which the more traditional rings sit.
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