moons of Uranus

Uranus has 27 known moons, placing it third, by this reckoning, behind Jupiter (63) and Saturn (33). The first two were discovered by William Herschel in 1787, and named, by his son, after characters from Shakespeare’s A Midsummer Nights Dream, Titania and Oberon. Two more moons were found by William Lassell in 1851 and named Ariel and Umbriel; G. Kuiper discovered Miranda in 1948. All the moons of Uranus are named after characters from Shakespeare or Alexander Pope. Voyager 2’s flyby in January 1986 led to the discovery of another 10. Twelve additional moons have since been discovered by telescope.

In an unusual move, in late 2001, the International Astronomical Union stripped the title of “moon” from a small body seen in images taken by Voyager and previously reported to be orbiting Uranus. The IAU concluded that there wasn't yet enough data to confirm that the object, designated S/1986 U10, is a satellite. It appeared to be in nearly the same orbit as another moon, Belinda, about 75,000 km from Uranus, and, based on its brightness in the Voyager images, to have a diameter of about 40 km. S/1986 U 10 has not been seen since the Voyager 2 discovery, despite observing efforts that have discovered several other small moons orbiting the planet.

Two of the most recently discovered satellites, Cupid (S/2003 U1) and Mab (S/2003 U2), belong to the inner collection of satellites, each orbiting Uranus in less than a day. Indeed, it's hard to understand how the inner swarm of 13 Uranian moons, which are so close together that they must be gravitationally unstable, can coexist. All the moons from S2001/U3 out move in retrograde orbits. Click on each of the satellite names that appear in orange in the table below for further information.

moon	semimajor axis (km)	orbital period (days)	orbital eccentricity	orbital inclination (^o)	diameter (km)
Cordelia	49,750	0.335	0.0003	0.085	50 × 36
Ophelia	53,760	0.376	0.0099	0.104	54 × 38
Bianca	59,170	0.435	0.0009	0.193	64 × 46
Cressida	61,770	0.464	0.0004	0.006	92 × 74
Desdemona	62,660	0.474	0.0001	0.113	90 × 54
Juliet	64,360	0.493	0.0007	0.065	150 × 74
Portia	66,100	0.513	0.0001	0.060	156 × 126
Rosalind	69,930	0.558	0.0001	0.279	72 × 72
Cupid	74,800	0.618	0.0013	0.1?	~18
Belinda	75,260	0.624	0.0001	0.031	81 ± 16
Perdita	76,420	0.638	0.0012	0.0	30 × 30
Puck	86,000	0.762	0.0001	0.319	162 ± 4
Mab	97,730	0.923	0.0025	0.134	~25
Miranda	129,390	1.413	0.0013	4.232	472
Ariel	191,020	2.520	0.0012	0.260	1,158
Umbriel	266,300	4.144	0.0039	0.205	1,169
Titania	435,910	8.706	0.0011	0.340	1,578
Oberon	583,520	13.46	0.0014	0.058	1,523
Francisco	4,275,900	267.12 (r)	0.1369	147.460	~22
Caliban	7,164,900	579.39 (r)	0.0790	139.885	~72
Stephano	7,952,200	677.48 (r)	0.1444	141.874	~32
Trinculo	8,501,300	748.83 (r)	0.2177	166.25	~18
Sycorax	12,189,100	1285.62 (r)	0.5137	152.447	~150
Margaret	14,420,400	1654.32 (r)	0.7979	51.456	~20
Prospero	16,162,200	1962.95 (r)	0.3296	146.17	~25
Setebos	17,419,300	2196.35 (r)	0.5722	145.884	~24
Ferdinand	20,507,100	2805.51 (r)	0.4312	167.346	~20

Features in the Uranus system.
Credit: NASA, ESA, and A. Feild (STScI)

Archived news

Moongazing reveals the chaotic world of Uranus (Dec 28, 2005)

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• PLANETS AND MOONS

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