Uranus: Moons and Rings

Moons

Uranus’s moons have had a long and tangled history. The first two moons, Titania and Oberon, were discovered in 1787 by the man who had discovered Uranus six years earlier, William Herschel. He named them after the king and queen of fairies in Shakespeare’s A Midsummer Night’s Dream, provoking a protest from the German ambassador (among others) who felt that the satellites should be given a more international and classical name. The name stuck, however, and now all of the moons of Uranus have been given the names of characters drawn from the works of either Shakespeare or Pope.

Naming the moons of Uranus, however, proved less troublesome than keeping track of them. Most are so small that they cannot be detected from Earth. Scientists were tracking the small satellites until the Hubble Space Telescope could be launched. But by the time Hubble sighted Uranus, Ophelia and Cordelia were lost. Due to the influence these moons exerted on the rings, however, they were eventually found again. A decade later, scientists going over the pictures taken by Voyager 2 discovered another moon. Several years later another was found. Now Uranus boasts 21 moons—five more than the leading contender, Saturn, which has fifteen. It is likely that at least one more small satellite is still hiding somewhere in the complicated web of moons and rings that encircle Uranus. In order from the planet, the satellites are 1999U3 (still unnamed), Cordelia, Ophelia, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Belinda, 1986U10 (still unnamed), Puck, Miranda, Ariel, Umbriel, Titania, Oberon, Caliban, and 1999U2 (still unnamed).

Name	Distance (km)	Radius (km)	Mass (kg)	Discoverer (Year)
1986U10	75,000	20	Unknown	Karkoschka (1999)
1999U1	10,000,000	20	Unknown	Kavelaars
1999U2	25,000,000	15	Unknown	Gladman (1999)
1999U3	20,000	Unknown	Unknown	Holman (1999)
Ariel	191,000	579	1.27 x 10²¹	Lassell (1985)
Belinda	75,000	34	Unknown	Voyager (1986)
Bianca	59,000	22	Unknown	Voyager (1986)
Caliban	7,100,000	30	Unknown	Gladman (1997)
Cordelia	50,000	13	Unknown	Voyager (1986)
Cressida	62,000	33	Unknown	Voyager (1986)
Desdemona	63,000	29	Unknown	Voyager (1986)
Juliet	64,000	42	Unknown	Voyager (1986)
Miranda	130,000	236	6.30 x 10¹⁹	Kuiper (1948)
Oberon	583,000	761	3.03 x 10²¹	Herschel (1787)
Ophelia	54,000	16	Unknown	Voyager (1986)
Portia	66,000	55	Unknown	Voyager (1986)
Puck	86,000	77	Unknown	Voyager (1986)
Rosalind	70,000	27	Unknown	Voyager (1986)
Sycorax	12,200,000	60	Unknown	Nicholson (1997)
Titania	436,000	789	3.49 x 10²¹	Herschel (1787)
Umbriel	266,000	585	1.27 x 10²¹	Lassell (1851)

Rings

Voyager 2 discovered Uranus’s faint rings. Interestingly enough, two of the moons that the probe discovered, Cordelia and Ophelia, have some part in maintaining them. They are “shepherd” moons that keep the constituent particles of the ring in tight order. Cordelia and Ophelia maintain the epsilon ring.

Copyright © 2000 by Gary Chan and Matthew McDermott. All rights reserved.