The Moons of Uranus

uranusmoonsThe astronomer William Herschel discovered Uranus, the 7th planet in the Solar System, and its first two moons, Oberon and Titania in 1787, just six years after discovering the planet itself. The planet Uranus has 27 known moons, most of which we didn’t discover until the space age. They range from Titania, 981 miles (1,579 kilometers) in diameter, to tiny Cupid, only 11 miles (18 km) in diameter. All satellites of Uranus are named for characters in William Shakespeare plays or characters from Alexander Pope’s “Rape of the Lock,” according to International Astronomical Union guidelines. Astronomers knew of five moons before the Voyager 2 spacecraft launched in 1977. The probe found an additional 10 when it swung by the system in 1986.

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Ariel_USGS
Ariel
miranda-uranus-moon-surface
Miranda

English astronomer William Lassell spotted Umbriel, the darkest of Uranus’ big moons, in 1851. In Voyager 2’s quick fly-by, scientists were unable to figure out how the surface got so dark, or why there is a bright ring on Umbriel’s surface that is 90 miles (140 kilometers) in diameter. Ariel, another find from Lassell in 1851, has the youngest and brightest known surface among the moons. Voyager 2 detected a silicate rock and water ice composition on this moon, with hints of carbon dioxide. The last find before the space age was perhaps the most bizarre moon of all — Miranda. Found by Gerard P. Kuiper at the McDonald Observatory in 1948, the moon appears to be a jumble of disconnected features. It’s unclear what made the mashed-up surface. Perhaps smaller meteorites melted the surface and caused slush to flow and freeze again.

Cordelia
Cordelia

When Voyager 2 skimmed closest to Uranus’ system in January 1986, its view turned up 10 new satellites within a month. Ophelia and Cordelia are sometimes called shepherd moons. They are close to Uranus’ Epsilon ring, with their gravitational influence essentially keeping the ring from falling apart. No one knows how big Cordelia is, or what its composition might be. Ophelia is believed to be 12 miles (20 kilometers) in diameter. Voyager 2 got a picture of Puck that showed a mottled, dark surface. Astronomers believe it is made of carbonaceous material, and assume that much of the rest of the moons are of the same material. A 2003 study of the moon suggested water ice is on its surface. Close-up pictures showed that Oberon is about half ice

Titania
Titania

and half rock, with craters peppering its surface. Titania has fault lines running across its surface, hinting at past or present seismic activity.

Most of the other moons were so small and far away from the spacecraft that little is known about their composition Uranus_Cressidaand in some cases, their sizes. Belinda and Cressida have low reflectivity, indicating they are probably carbonaceous moons as Puck is. The other moons found right away were Portia, Rosalind, Juliet, Desdemona and Bianca. A 2001 study using the Hubble Space Telescope suggested these satellites (called the “Portia group”) all have similar compositions and orbits.

800px-Uranian_system_schematic-en.svgThe University of Arizona’s Erich Karkoschka found the moon Perdita in 1999 using public Voyager 2 images and comparing them to some taken by the Hubble Space Telescope. Caliban, found by a team at the Palomar Observatory in 1997, moves in an inclined opposite orbit to the rotation of Uranus. The same team also found Sycorax, which appears red in telescopes and also has a retrograde orbit. Three more discoveries happened in 1999 using the Canada-France-Hawaii Telescope at the Mauna Kea Observatory: Setebos, Prospero and Stephano. In 2001, a team at the Cerro Tololo Inter-American Observatory in Chile found Trinculo,  Francisco and Ferdinand. The latest finds took place in 2003 when Hubble spotted Mab and Cupid, while Margaret was found using the Subaru 8.2-meter reflector at the Mauna Kea Observatory.

Credits: Space, Wikipedia.