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Uranus' Moons


Uranus has 27 known moons. Titania, the largest, is about half the size of our own moon. The moons are all made of ice and rock. Most of the moons, including Titania, Oberon, and Umbriel, seem to be "normal" moons without anything interesting; however, Miranda and Ariel seem to have had violent pasts (see below). Most of the moons appear to be captured asteroids due to their size and orbits.


The two innermost moons of Uranus, Cordelia and Ophelia, act as shepherd moons. They have orbits on either side of the last ring, epsilon, which keeps it narrow. Scientists believe that each of the other rings have shepherds, too, but they must have been too small for the Voyagers' cameras to detect.

The next eight moons are Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Belinda, and Puck, all named for Shakespearian characters. Inside of Belinda's orbit is a moon designated as S/1986 U10. It has not been named because there is controversy over whether or not it really exists; the International Astronomical Union (IAU), the only official naming body has yet to designate it as a real moon.

Next out is Miranda. It is the smallest of Uranus' moons that is visible from the Earth. It has some of the most interesting surface features in the solar system. First, it has a cliff that is about 19 km (12 miles) high. If this were scaled to be on Earth, it would reach into the orbit of spacecraft. It also has three long, rectangular shapes, called "coronae." Scientists think that at one time the pull of the other moons warmed the interior and caused the ice in Miranda to start to rise. The coronae mark where it froze before coming to the surface.Ariel

Ariel (right), next, is covered with complex fractures and grooves. Probably they are the result of ice seeping to the surface, then freezing and expanding. Ariel also has lava-filled valleys. The lava is made of a mixture of water and liquid ammonia

TitaniaNext comes Umbriel, equal in size to Ariel, but with a bland, nondescript surface.

OberonNext out is Titania (left) and Oberon (right). Titania is the biggest moon of Uranus. It looks like a larger version of Ariel. Oberon is only a little smaller than Titania. Oberon has a crater-peppered surface of little interest. However, it does posses a mountain that is twice the height of Mt. Everest.

The next moons, Caliban, Stephano, Sycorax, Prospero, and Setebos were discovered in just the past few years by re-examining Voyager 2 images. Very little is known about them, except that they all have retrograde - they orbit in the opposite direction of the planet's spin - orbits, leading to the conclusion that they are captured asteroids rather than native to the Uranian system. Inside of Sycorax's orbit is a moon designated as Trinculo, which also has retrograde motion.

Data for Uranus' Moons


Discovery Date
Distance from Uranus (103 km)
Orbital Period (days)
Mass (1020 kg)
Radius (km)
Miranda (UV) 1948 G. Kuiper 129.39 1.413479 0.66 240 x 234.2 x 232.9
Ariel (UI) 1851 W. Lassel 191.02 2.520379 13.5 581.1 x 577.9 x 577.7
Umbriel (UII) 1851 W. Lassel 266.30 4.144177 11.7 584.7
Titania (UIII) 1787 W. Herschel 435.91 8.705872 35.2 788.9
Oberon (UIV) 1787 W. Herschel 583.52 13.463239 30.1 761.4
Cordelia (UVI, S/1986 U7) 1986 Voyager 2 49.77 0.335034   20
Ophelia (UVII, S/1986 U8) 1986 Voyager 2 53.79 0.376400   21
Bianca (UVIII, S/1986 U9) 1986 Voyager 2 59.17 0.434579   27
Cressida (UIX, S/1986 U3) 1986 Voyager 2 61.78 0.463570   40
Desdemona (UX, S/1986 U6) 1986 Voyager 2 62.68 0.473650   32
Juliet (UXI, S/1986 U2) 1986 Voyager 2 64.35 0.493065   47
Portia (UXII, S/1986 U1) 1986 Voyager 2 66.09 0.513196   68
Rosalind (UXIII, S/1986 U4) 1986 Voyager 2 69.94 0.558460   36
Cupid (S/2003 U2) 2003   74.8 0.618   12
Belinda (UXIV, S/1986 U5) 1986 Voyager 2 75.26 0.623527   40
Puck (UXV, S/1985 U1) 1985 Voyager 2 86.01 0.761833   81
Mab (S/2003 U1) 2003   97.7 0.923   16
Caliban (UXVI, S/1997 U1) 1997 Kavelaars, Gladman, Holman, et. Al 7230 579.5*   48
Stephano (UXX, S/1999 U2) 1999 Kavelaars, Gladman, Holman, et. Al 8002 676.5*   10
Sycorax (UXVII, S/1997 U2) 1997 Kavelaars, Gladman, Holman, et. Al 12,179 1283.4*   95
Margaret (UXXIII, S/2003 U3) 2003   14,345 1694.8   6
Prospero (UXVIII, S/1999 U3) 1999 Kavelaars, Gladman, Holman, et. Al 16,418 1992.8*   15
Setebos (UXIX, S/2001) 1999 Kavelaars, Gladman, Holman, et. Al 17,459 2202.3*   15
Trinculo (UXXI, S/2001 U1) 2001   8571 758.1*   5
S/1986 U10 1986   76.4 0.638   40
S/2001 U2 2001   21,000 2823.4*   6
S/2001 U3 2001   4280 266.6*   6

* This indicates that the moon orbits in a retrograde - the opposite direction to the planet's spin - motion.

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