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Dust particles in Uranian rings
Dust particles in Uranian rings

When two teams of scientists set up to watch Uranus pass in front of star SAO 158687 in 1977, they expected a rare chance to observe a distant planet. Instead, they made a major discovery: Uranus, like Saturn, is encircled with a band of rings.

As the observers in the Kuiper Airborne Observatory and the Perth Observatory in Australia watched, the star appeared to blink out briefly several times. The blinking was caused by the rings blocking the starlight. The Australian team was so surprised they missed three rings as they tried to figure out why the starlight signal kept disappearing.

The Kuiper team had a better vantage point and were first to publish the surprising news that Uranus was encircled by five narrow rings, which they named Alpha, Beta, Gamma, Delta and Epsilon in order of increasing distance from the planet. The Perth team identified six distinct dips in the starlight, which they named rings 1 through 6.

After careful analysis and a closer view courtesy of the Voyager 2 spacecraft in 1986, scientists have now identified 13 known rings around Uranus. [Editor's note: The discovery of two new rings was announced on December 22, 2005. See HubbleSite News Release Archive.] In order of increasing distance from the planet, they are 1986U2R, 6, 5, 4, Alpha, Beta, Eta, Gamma, Delta, Lambda, Epsilon, Nu and Mu. Some of the larger rings are surrounded by belts of fine dust.

Reference: USGS Astrogeology: Gazetteer of Planetary Nomenclature -- Ring Nomenclature

Uranus's Rings
Ring Name: Zeta (1986 U2R)
Distance*: 39,600 km
Width: 3,500 (plus 5,000 km extension inwards) km
Thickness: 0.1 km
Albedo: 0.03

Ring Name: 6
Distance*: 41,840 km
Width: 1 km - 3 km
Thickness: 0.1 km
Albedo: 0.03

Ring Name: 5
Distance*: 42,230 km
Width: 2 km - 3 km
Thickness: 0.1 km
Mass: 0.1 kg
Albedo: 0.03

Ring Name: 4
Distance*: 42,580 km
Width: 2 km - 3 km
Thickness: .1 km
Mass: .1 kg
Albedo: 0.03

Ring Name: Alpha
Distance*: 44,720 km
Width: 7 km - 12 km
Thickness: 0.1 km
Albedo: 0.03

Ring Name: Beta
Distance*: 45,670 km
Width: 7 km - 12 km
Thickness: 0.1 km
Albedo: 0.03

Ring Name: Eta
Distance*: 47,190 km
Width: 0 km - 2 km
Thickness: 0.1 km
Albedo: 0.03

Ring Name: Gamma
Distance*: 47,630 km
Width: 1 km - 4 km
Thickness: 0.1 km
Albedo: 0.03

Ring Name: Delta
Distance*: 48,290 km
Width: 3 km - 9 km
Thickness: 0.1 km
Albedo: 0.03

Ring Name: Lambda (1986 U1R)
Distance*: 50,024 km
Width: 2 km - 3 km
Thickness: 0.1 km
Albedo: 0.03

Ring Name: Epsilon
Distance*: 51,140 km
Width: 20 km - 100 km
Thickness: < 15 km
Albedo: 0.03

Ring Name: Nu (R/2003 U 2)
Distance*: 67,300 km
Width: 3,800 km

Ring Name: Mu (R/2003 U 1)
Distance*: 97,700 km
Width: 17,000 km

* The distance is measured from the planet center to the start of the ring.
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Last Updated: 2 Apr 2014