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Uranus Moons
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Uploaded on Feb 1, 2010
Uranus, the seventh planet of the Solar System, has 27 known moons, all of which are named after characters from the works of William Shakespeare and Alexander Pope. William Herschel discovered the first two moons, Titania and Oberon, in 1787, and the other spherical moons were discovered in 1851 by William Lassell (Ariel and Umbriel) and in 1948 by Gerard Kuiper (Miranda).The remaining moons were discovered after 1985, either during the Voyager 2 flyby mission or with the aid of advanced Earth-based telescopes. Uranian moons are divided into three groups: thirteen inner moons, five major moons, and nine irregular moons. The inner moons are small dark bodies that share common properties and origins with the planet's rings. The five major moons are massive enough to have achieved hydrostatic equilibrium, and four of them show signs of internally driven processes such as canyon formation and volcanism on their surfaces. The largest of these five, Titania, is 1,578 km in diameter and the eighth-largest moon in the Solar System, and about 20 times less massive than Earth's Moon. Uranus's irregular moons have elliptical and strongly inclined (mostly retrograde) orbits at great distances from the planet.
Uranus has five major moons: Miranda, Ariel, Umbriel, Titania and Oberon. They range in diameter from 472 km for Miranda to 1578 km for Titania. All large moons are relatively dark objects: their geometrical albedo varies in the range of 3050%, while bond albedo is within the range of 1023%. Umbriel is the darkest moon and Ariel is the brightest. The masses of the moons range from 6.7 × 1019 kg (Miranda) to 3.5 × 1021 kg (Titania)—for comparison, Earth's Moon has mass of 7.5 × 1022 kg.The major moons of Uranus are believed to have formed in the accretion disc, which existed around Uranus for some time after its formation or resulted from the large impact suffered by Uranus early in its history.
All major moons comprise approximately equal amounts rock and ice, except Miranda, which is made primarily of ice. The ice component may include ammonia and carbon dioxide.Their surfaces are heavily cratered, though all of them (except Umbriel) show signs of endogenic resurfacing in the form of lineaments (canyons) and, in the case of Miranda, ovoid race-track like structures called coronae. Extensional processes associated with upwelling diapirs are likely responsible for the origin of the coronae. Ariel appears to have the youngest surface with the fewest impact craters, while Umbriel's appears oldest. A past 3:1 orbital resonance between Miranda and Umbriel and a past 4:1 resonance between Ariel and Titania are thought to be responsible for the heating that caused substantial endogenic activity on Miranda and Ariel. One of the reasons believed to prove such past resonance is Miranda's unusually high orbital inclination (4.34°) for a body so close to the planet. The largest Uranian moons may be internally differentiated, with rocky cores at their centers surrounded by ice mantles. Titania and Oberon may harbor liquid water oceans at the core/mantle boundary. The major moons of Uranus are airless bodies. For instance, Titania was shown to possess no atmosphere at a pressure larger than 1020 nanobar.
The path of the Sun in the local sky over a local day during Uranus' and its major moons' Summer solstice is quite different than that seen on most other Solar System planets. The major moons have almost exactly the same rotational axial tilt as Uranus', and thus these axises are parallel to Uranus' axis.The Sun would look to be tracing out a circular path around Uranus' celestial pole in the sky, at the closest about 7 degrees away from it. And would be seen nearly due north or due south, depending on which hemisphere you are standing in, near the equator. At mid latitudes you'd see the Sun trace a circular path about 15 degrees diameter in the sky, and never set, over the course of the local day.
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