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Uranus in true and false color
Uranus in true and false color (Click on the image for a larger view)

All nine previously known rings of Uranus were photographed and measured, as were other new rings and ringlets in the Uranian system. These observations showed that Uranus's rings are distinctly different from those at Jupiter and Saturn.

Radio measurements showed the outermost ring, the epsilon, to be composed mostly of ice boulders several feet across. However, a very tenuous distribution of fine dust also seems to be spread throughout the ring system.

Incomplete rings and the varying opacity in several of the main rings leads scientists to believe that the ring system may be relatively young and did not form at the same time as Uranus. The particles that make up the rings may be remnants of a moon that was broken by a high-velocity impact or torn up by gravitational effects.

To date, two new rings have been positively identified. The first, 1986 U1R, was detected between the outermost of the previously known rings -- epsilon and delta -- at a distance of 50,000 kilometers (31,000 miles) from Uranus's center. It is a narrow ring like the others. The second, designated 1986 U2R, is a broad region of material perhaps 3,000 kilometers (1,900 miles) across and just 39,000 kilometers (24,000 miles) from the planet's center.

The number of known rings may eventually grow as a result of observations by the Voyager 2 photopolarimeter instrument. The sensor revealed what may be a large number of narrow rings -- or possibly incomplete rings or ring arcs -- as small as 50 meters (160 feet) in width.

The individual ring particles were found to be of low reflectivity. At least one ring, the epsilon, was found to be gray in color. Important clues to Uranus's ring structure may come from the discovery that two small moons --Cordelia and Ophelia -- straddle the epsilon ring. This finding lends credence to theories that small moonlets may be responsible for confining or deflecting material into rings and keeping it from escaping into space. Eighteen such satellites were expected to have been found, but only two were photographed.

The sharp edge of the epsilon ring indicates that the ring is less than 150 meters (500 feet) thick and that particles near the outer edge are less than 30 meters (100 feet) in diameter.

The epsilon ring is surprisingly deficient in particles smaller than about the size of a beachball. This may be due to atmospheric drag from the planet's extended hydrogen atmosphere, which probably siphons smaller particles and dust from the ring.

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