Name Size (km) Orbit (km) Period (hh:mm:ss)
Cordelia 50 x 36 x 36 49,751 08:02:26
Ophelia 54 x 38 x 38 53,764 09:02:01
Bianca 64 x 46 x 46 59,165 10:25:48 Portia Group
Cressida 92 x 74 x 74 61,766 11:07:32 Portia Group
Desdemona 90 x 54 x 54 62,658 11:22:03 Portia Group
Juliet 150 x 74 x 74 64,360 11:50:01 Portia Group
Portia 156 x 126 66,097 12:19:00 Portia Group
Rosalind 72 69,927 13:24:11 Portia Group
Cupid 18 74,800 14:49:55 Portia Group
Belinda 128 x 64 x 64 75,255 14:57:52 Portia Group
Perdita 30 76,420 15:18:43 Portia Group
Puck 162 86,004 18:17:02
Mab 10 (or poss. 25) 97,734 22:09:07
Miranda 471.6 129,390 33:55:25
WILLIAM & DEBORAH HILLYARD
A collage of Voyager 2 photographs showing the major moons of Uranus in correct relative sizes.  From left to right: Puck, Miranda, Ariel, Umbriel, Titania and Oberon. 

Solar System -

Uranus

Uranus' Moons

A schematic (to-scale) of the ring & moon system of Uranus
Uranus has 27 identified moons to date, three of which (Ariel, Umbriel & Belinda) are named from a poem by Alexander Pope, while the remainder are named after characters from Shakespeare.  The table to the right lists the moons in order from Cordelia, closest to Uranus, outwards with their diameters in kilometers.  The smaller moons are, as usual, far from spherical, but the measurement indicates a nominal diameter.  Where available, I have linked to photographs of the moon. 

The thirteen moons out to the newly-discovered (in 2003) Mab are considered "inner moons".  They are all orbiting within the ring system, and some, Cordelia & Ophelia, for example, act as "shepherd moons" keeping the rings in place.  The orbits of these moons are fairly chaotic and, over millions of years, the orbits cross each other, leading to the risk of collisions.  This may well be how the rings originated.  These moons formed from an accretion disk that was either present when Uranus formed, or resulted from the possible collision event Uranus suffered which tilted it so far on its axis. 

The next five moons are the largest.  Miranda is made primarily of ice, probably including ammonia and carbon dioxide.  The other four are roughly half ice and half rock, with rocky cores covered with an ice mantle.  While all five are cratered, all but Umbriel show signs of geological activity that has resurfaced the planet in the past. 

The nine outer moons are all small and irregular, and are almost certainly captured objects.  Unlike all the other moons, the outer moons, except Margaret, have retrograde orbits.  Margaret's orbit, while prograde, has a large eccentricity. 

The four largest moons make up 99.2% of the mass of Uranus' moons system.  Miranda is a further 0.7% while the remaining 22 moons make up barely 0.1%.  Oberon, the furthest of the large moons from Uranus, orbits about 583,500 km (365,000 miles) from Uranus.  There is then a huge gap until we reach Francisco which orbits some 4,276,000 km (2,672,000 miles) from Uranus, with Ferdinand out at 20,900,000 plus km (13,060,000 miles). 
This montage shows Uranus and its five major moons.  The images are from the Voyager 2 spacecraft.  As shown here, the moons, from largest to smallest, are Ariel, Miranda, Titania, Oberon and Umbriel.
Links


Wikipedia has an excellent table with information about all of Uranus' Moons.  NASA also has more information on Uranus' Moons
Credit: NASA/JPL

Credit: NASA/Vzb83


Name Size (km) Orbit (km) Period (days)
Ariel 1,157.8 191,020 2.5204
Umbriel 1,169.4 266,300 4.1442
Titania 1,576.8 435,910 8.7059
Oberon 1,522.8 583,520 13.4632
Francisco 22 4,276,000 -266.5600
Caliban 72 7,231,000 -579.7300
Stephano 32 8,004,000 -677.3700
Trinculo 18 8,504,000 -749.2400
Sycorax 150 12,179,000 -1,288.2800
Margaret 20 14,345,000 1,687.0100
Prospero 50 16,256,000 -1,978.2900
Setebos 48 17,418,000 -2,225.2100
Ferdinand 20 20,901,000 -2,805.5100

Uranus' Moons - Characteristics
All sizes are approximate.  Orbits are the average distance to Uranus; the semi-major axis.  Negative periods, shown in italics, represent those satellites having retrograde orbits.  All the irregular moons from Francisco outwards have retrograde orbits except the tiny moon Margaret.  Most of the inner orbits, Cordelia to Oberon, have low eccentricity (less than 0.0025).  Francisco to Trinculo are somewhat more eccentric, while the outer four are highly eccentric in the range of about 0.37 to 0.66. 

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