FANDOM


Uranus moons

Uranus and its six largest moons compared at their proper relative sizes and relative positions. From left to right: Puck, Miranda, Ariel, Umbriel, Titania, and Oberon

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.[1] Uranus's 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 Uranus's rings. The five major moons are massive enough to have reached hydrostatic equilibrium, and four of them show signs of internally driven processes such as canyon formation and volcanism on their surfaces.[2] The largest of these five, Titania, is 1,578 km in diameter and the eighth-largest moon in the Solar System, and about one-twentieth the mass of the Moon. The orbits of the regular moons are nearly coplanar with Uranus's equator, which is tilted 97.77° to its orbit. Uranus's irregular moons have elliptical and strongly inclined (mostly retrograde) orbits at large distances from the planet.[3]

William Herschel discovered the first two moons, Titania and Oberon, in 1787, and the other three ellipsoidal moons were discovered in 1851 by William Lassell (Ariel and Umbriel) and in 1948 by Gerard Kuiper (Miranda).[1] These five have planetary mass, and so would be considered (dwarf) planets if they were in direct orbit about the Sun. The remaining moons were discovered after 1985, either during the Voyager 2 flyby mission or with the aid of advanced Earth-based telescopes.[2][3]

DiscoveryEdit

The first two moons to be discovered were Titania and Oberon, which were spotted by Sir William Herschel on January 11, 1787, six years after he had discovered the planet itself. Later, Herschel thought he had discovered up to six moons (see below) and perhaps even a ring. For nearly 50 years, Herschel's instrument was the only one with which the moons had been seen.[4] In the 1840s, better instruments and a more favorable position of Uranus in the sky led to sporadic indications of satellites additional to Titania and Oberon. Eventually, the next two moons, Ariel and Umbriel, were discovered by William Lassell in 1851.[5] The Roman numbering scheme of Uranus's moons was in a state of flux for a considerable time, and publications hesitated between Herschel's designations (where Titania and Oberon are Uranus II and IV) and William Lassell's (where they are sometimes I and II).[6] With the confirmation of Ariel and Umbriel, Lassell numbered the moons I through IV from Uranus outward, and this finally stuck.[7] In 1852, Herschel's son John Herschel gave the four then-known moons their names.[8]

No other discoveries were made for almost another century. In 1948, Gerard Kuiper at the McDonald Observatory discovered the smallest and the last of the five large, spherical moons, Miranda.[8][9] Decades later, the flyby of the Voyager 2 space probe in January 1986 led to the discovery of ten further inner moons.[2] Another satellite, Perdita, was retroactively discovered in 1999[10] after studying old Voyager photographs.[11]

Uranus was the last giant planet without any known irregular moons, but since 1997 nine distant irregular moons have been identified using ground-based telescopes.[3] Two more small inner moons, Cupid and Mab, were discovered using the Hubble Space Telescope in 2003.[12] As of 2015, the moon Margaret was the last Uranian moon discovered, and its characteristics were published in October 2003.[13]

Spurious moonsEdit

After Herschel discovered Titania and Oberon on January 11, 1787, he subsequently believed that he had observed four other moons: two on January 18 and February 9, 1790, and two more on February 28 and March 26, 1794. It was thus believed for many decades thereafter that Uranus had a system of six satellites, though the four latter moons were never confirmed by any other astronomer. Lassell's observations of 1851, in which he discovered Ariel and Umbriel, however, failed to support Herschel's observations; Ariel and Umbriel, which Herschel certainly ought to have seen if he had seen any satellites beside Titania and Oberon, did not correspond to any of Herschel's four additional satellites in orbital characteristics. Herschel's four spurious satellites were thought to have sidereal periods of 5.89 days (interior to Titania), 10.96 days (between Titania and Oberon), 38.08 days, and 107.69 days (exterior to Oberon).[14] It was therefore concluded that Herschel's four satellites were spurious, probably arising from the misidentification of faint stars in the vicinity of Uranus as satellites, and the credit for the discovery of Ariel and Umbriel was given to Lassell.[15]

NamesEdit

Main article: Naming of moons

Although the first two Uranian moons were discovered in 1787, they were not named until 1852, a year after two more moons had been discovered. The responsibility for naming was taken by John Herschel, son of the discoverer of Uranus. Herschel, instead of assigning names from Greek mythology, named the moons after magical spirits in English literature: the fairies Oberon and Titania from William Shakespeare's A Midsummer Night's Dream, and the sylphs Ariel and Umbriel from Alexander Pope's The Rape of the Lock (Ariel is also a sprite in Shakespeare's The Tempest). The reasoning was presumably that Uranus, as god of the sky and air, would be attended by spirits of the air.[16]

Subsequent names, rather than continuing the airy spirits theme (only Puck and Mab continued the trend), have focused on Herschel's source material. In 1949, the fifth moon, Miranda, was named by its discoverer Gerard Kuiper after a thoroughly mortal character in Shakespeare's The Tempest. The current IAU practice is to name moons after characters from Shakespeare's plays and The Rape of the Lock (although at present only Ariel, Umbriel, and Belinda have names drawn from the latter; all the rest are from Shakespeare). At first, the outermost moons were all named after characters from one play, The Tempest; but with Margaret being named from Much Ado About Nothing that trend has ended.[8]

Masses of Uranian moons-en

The relative masses of the Uranian moons. The five rounded moons vary from Miranda at 0.7% to Titania at almost 40% of the total mass. The other moons collectively constitute 0.1%, and are barely visible at this scale.

Some asteroids share names with moons of Uranus: 171 Ophelia, 218 Bianca, 593 Titania, 666 Desdemona, 763 Cupido, and 2758 Cordelia.

Characteristics and groupsEdit

Uranian system schematic-en

Schematic of the Uranian moon–ring system

The Uranian satellite system is the least massive among those of the giant planets. Indeed, the combined mass of the five major satellites is less than half that of Triton (the seventh-largest moon in the Solar System) alone.Template:Efn The largest of the satellites, Titania, has a radius of 788.9 km,[17] or less than half that of the Moon, but slightly more than that of Rhea, the second-largest moon of Saturn, making Titania the eighth-largest moon in the Solar System. Uranus is about 10,000 times more massive than its moons.Template:Efn

Inner moonsEdit

As of 2015, Uranus is known to have 13 inner moons.[12] Their orbits lie inside that of Miranda. All inner moons are intimately connected to the rings of Uranus, which probably resulted from the fragmentation of one or several small inner moons.[18] The two innermost moons (Cordelia and Ophelia) are as shepherds of Uranus's ε ring, whereas the small moon Mab is a source of Uranus's outermost μ ring.[12]

At 162 km, Puck is the largest of the inner moons of Uranus and the only one imaged by Voyager 2 in any detail. Puck and Mab are the two outermost inner satellites of Uranus. All inner moons are dark objects; their geometrical albedo is less than 10%.[19] They are composed of water ice contaminated with a dark material—probably radiation-processed organics.[20]

The small inner moons constantly perturb each other. The system is chaotic and apparently unstable. Simulations show that the moons may perturb each other into crossing orbits, which may eventually result in collisions between the moons.[12] Desdemona may collide with either Cressida or Juliet within the next 100 million years.[21]

Uranian moon montage

The five largest moons of Uranus compared at their proper relative sizes and brightnesses. From left to right (in order of increasing distance from Uranus): Miranda, Ariel, Umbriel, Titania, and Oberon.

Large moonsEdit

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.[17] All these moons are relatively dark objects: their geometrical albedo varies between 30 and 50%, whereas their Bond albedo is between 10 and 23%.[19] Umbriel is the darkest moon and Ariel the brightest. The masses of the moons range from 6.7Template:E-sp kg (Miranda) to 3.5Template:E-sp kg (Titania). For comparison, the Moon has a mass of 7.5Template:E-sp kg.[22] The major moons of Uranus are thought to have formed in the accretion disc, which existed around Uranus for some time after its formation or resulted from a large impact suffered by Uranus early in its history.[23][24]

Uranusmoonsummer

Artist's conception of the Sun's path in the summer sky of a major moon of Uranus (which shares Uranus's axial tilt)

All major moons comprise approximately equal amounts rock and ice, except Miranda, which is made primarily of ice.[25] The ice component may include ammonia and carbon dioxide.[26] 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.[2] Extensional processes associated with upwelling diapirs are likely responsible for the origin of the coronae.[27] Ariel appears to have the youngest surface with the fewest impact craters, while Umbriel's appears oldest.[2] 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.[28][29] One piece of evidence for such a past resonance is Miranda's unusually high orbital inclination (4.34°) for a body so close to the planet.[30][31] The largest Uranian moons may be internally differentiated, with rocky cores at their centers surrounded by ice mantles.[25] Titania and Oberon may harbor liquid water oceans at the core/mantle boundary.[25] The major moons of Uranus are airless bodies. For instance, Titania was shown to possess no atmosphere at a pressure larger than 10–20 nanobar.[32]

The path of the Sun in the local sky over the course of a local day during Uranus's and its major moons' summer solstice is quite different from that seen on most other Solar System worlds. The major moons have almost exactly the same rotational axial tilt as Uranus's (their axes are parallel to that of Uranus).[2] The Sun would appear to follow a circular path around Uranus's celestial pole in the sky, at the closest about 7 degrees from it.Template:Efn Near the equator, it would be seen nearly due north or due south (depending on the season). At latitudes higher than 7°, the Sun would trace a circular path about 15 degrees diameter in the sky, and never set.

TheIrregulars URANUS

Irregular moons of Uranus. The X axis is labeled in Gm (million km) and in the fraction of the Hill sphere's radius. The eccentricity is represented by the yellow segments (extending from the pericentre to the apocentre) with the inclination represented on the Y axis.

Irregular moonsEdit

As of 2005 Uranus is known to have nine irregular moons, which orbit it at a distance much greater than that of Oberon, the furthest of the large moons. All the irregular moons are probably captured objects that were trapped by Uranus soon after its formation.[3] The diagram illustrates the orbits of those irregular moons discovered so far. The moons above the X axis are prograde, those beneath are retrograde. The radius of the Uranus's Hill sphere is approximately 73 million km.[3]

Uranus's irregular moons range in size from 120–200 km (Sycorax) to about 20 km (Trinculo).[3] Unlike Jupiter's irregulars, Uranus's show no correlation of axis with inclination. Instead, the retrograde moons can be divided into two groups based on axis/orbital eccentricity. The inner group includes those satellites closer to Uranus (a < 0.15 rH) and moderately eccentric (~0.2), namely Francisco, Caliban, Stephano, and Trinculo.[3] The outer group (a > 0.15 rH) includes satellites with high eccentricity (~0.5): Sycorax, Prospero, Setebos, and Ferdinand.[3]

The intermediate inclinations 60° < i < 140° are devoid of known moons due to the Kozai instability.[3] In this instability region, solar perturbations at apoapse cause the moons to acquire large eccentricities that lead to collisions with inner satellites or ejection. The lifetime of moons in the instability region is from 10 million to a billion years.[3]

Margaret is the only known irregular prograde moon of Uranus, and it currently has the most eccentric orbit of any moon in the Solar System, though Neptune's moon Nereid has a higher mean eccentricity. As of 2008, Margaret's eccentricity is 0.7979.[33]

ListEdit

Key

Inner moons
 

Major moons
 

Irregular moons (retrograde)
°
Irregular moon (prograde)

The Uranian moons are listed here by orbital period, from shortest to longest. Moons massive enough for their surfaces to have collapsed into a spheroid are highlighted in light blue and bolded. Irregular moons with retrograde orbits are shown in dark grey. Margaret, the only known irregular moon of Uranus with a prograde orbit, is shown in light grey.

Uranian moons
Order
Template:Efn
Label
Template:Efn
Name Pronunciation
(key)
Image Diameter
(km)Template:Efn
Mass
(Template:E kg)Template:Efn
Semi-major axis
(km)[34]
Orbital period
(d)[34]Template:Efn
Inclination
(°)[34]Template:Efn
Eccentricity
[35]
Discovery
year
[1]
Discoverer
[1]
1 Template:Sort Template:Hid Cordelia Template:IPAc-en Uranus rings and two moons Template:Sort Template:Sort Template:Sort Template:Sort Template:Sort Template:Val 1986 Terrile
(Voyager 2)
2 Template:Sort Template:Hid Ophelia Template:IPAc-en Uranus rings and two moons Template:Sort Template:Sort Template:Sort Template:Sort Template:Sort Template:Val 1986 Terrile
(Voyager 2)
3 Template:Sort Bianca Template:IPAc-en Bianca-luna-urano Template:Sort Template:Sort Template:Sort Template:Sort Template:Sort Template:Val 1986 Smith
(Voyager 2)
4 Template:Sort Template:Hid Cressida Template:IPAc-en Uranus-Portia-Cressida-Ophelia-NASA Template:Sort Template:Sort Template:Sort Template:Sort Template:Sort Template:Val 1986 Synnott
(Voyager 2)
5 Template:Sort Template:Hid Desdemona Template:IPAc-en Uranus-Desdemona-NASA Template:Sort Template:Sort Template:Sort Template:Sort Template:Sort Template:Val 1986 Synnott
(Voyager 2)
6 Template:Sort Template:Hid Juliet Template:IPAc-en Uranus-Juliet-NASA Template:Sort Template:Sort Template:Sort Template:Sort Template:Sort Template:Val 1986 Synnott
(Voyager 2)
7 Template:Sort Template:Hid Portia Template:IPAc-en Uranus-Portia-Cressida-Ophelia-NASA Template:Sort Template:Sort Template:Sort Template:Sort Template:Sort Template:Val 1986 Synnott
(Voyager 2)
8 Template:Sort Template:Hid Rosalind Template:IPAc-en Rosalind1 Template:Sort Template:Sort Template:Sort Template:Sort Template:Sort Template:Val 1986 Synnott
(Voyager 2)
9 Template:Sort Template:Hid Cupid Template:IPAc-en Cupid moon Template:Sort Template:Sort Template:Sort Template:Sort Template:Sort Template:Val 2003 Showalter and
Lissauer
10 Template:Sort Template:Hid Belinda Template:IPAc-en
Belinda
Template:Sort Template:Sort Template:Sort Template:Sort Template:Sort Template:Val 1986 Synnott
(Voyager 2)
11 Template:Sort Template:Hid Perdita Template:IPAc-en Perdita feat Template:Sort Template:Sort Template:Sort Template:Sort Template:Sort Template:Val 1999 Karkoschka
(Voyager 2)
12 Template:Sort Template:Hid Puck Template:IPAc-en
Puck
Template:Sort Template:Sort Template:Sort Template:Sort Template:Sort Template:Val 1985 Synnott
(Voyager 2)
13 Template:Sort Template:Hid Mab Template:IPAc-en
Mab moon
Template:Sort Template:Sort Template:Sort Template:Sort Template:Sort Template:Val 2003 Showalter and
Lissauer
14 Template:Sort Template:Hid Miranda Template:IPAc-en
PIA18185 Miranda&#039;s Icy Face
Template:Sort Template:Sort Template:Sort Template:Sort Template:Sort Template:Val 1948 Kuiper
15 Template:Sort Template:Hid Ariel Template:IPAc-en
Ariel (moon)
Template:Sort Template:Sort Template:Sort Template:Sort Template:Sort Template:Val 1851 Lassell
16 Template:Sort Template:Hid Umbriel Template:IPAc-en
PIA00040 Umbrielx2.47
Template:Sort Template:Sort Template:Sort Template:Sort Template:Sort Template:Val 1851 Lassell
17 Template:Sort Template:Hid Titania Template:IPAc-en
Titania (moon) color, edited
Template:Sort Template:Sort Template:Sort Template:Sort Template:Sort Template:Val 1787 Herschel
18 Template:Sort Template:Hid Oberon Template:IPAc-en
Voyager 2 picture of Oberon
Template:Sort Template:Sort Template:Sort Template:Sort Template:Sort Template:Val 1787 Herschel
19 Template:Sort Template:Hid Francisco Template:IPAc-en Uranus moon 021002 02 Template:Sort Template:Sort Template:Sort Template:Sort 147.459° Template:Val 2003Template:Efn Holman et al.
20 Template:Sort Template:Hid Caliban Template:IPAc-en Caliban feat Template:Sort Template:Sort Template:Sort Template:Sort 139.885° Template:Val 1997 Gladman et al.
21 Template:Sort Template:Hid Stephano Template:IPAc-en Stephano - Uranus moon Template:Sort Template:Sort Template:Sort Template:Sort 141.873° Template:Val 1999 Gladman et al.
22 Template:Sort Template:Hid Trinculo Template:IPAc-en Template:Sort Template:Sort Template:Sort Template:Sort 166.252° Template:Val 2001 Holman et al.
23 Template:Sort Template:HidSycorax Template:IPAc-en Sycorax Template:Sort Template:Sort Template:Sort Template:Sort 152.456° Template:Val 1997 Nicholson et al.
24 Template:Sort °Template:Hid Margaret Template:IPAc-en Template:Sort Template:Sort Template:Sort Template:Sort Template:Sort Template:Val 2003 Sheppard and
Jewitt
25 Template:Sort Template:Hid Prospero Template:IPAc-en Prospero discovery image Template:Sort Template:Sort Template:Sort Template:Sort 146.017° Template:Val 1999 Holman et al.
26 Template:Sort Template:Hid Setebos Template:IPAc-en Uranus - Setebos image Template:Sort Template:Sort Template:Sort Template:Sort 145.883° Template:Val 1999 Kavelaars et al.
27 Template:Sort Template:Hid Ferdinand Template:IPAc-en Ferdinand - Uranus moon Template:Sort Template:Sort Template:Sort Template:Sort 167.346° Template:Val 2003Template:Efn Holman et al.

Sources: NASA/NSSDC,[34] Sheppard, et al. 2005.[3] For the recently discovered outer irregular moons (Francisco through Ferdinand) the most accurate orbital data can be generated with the Natural Satellites Ephemeris Service.[33] The irregulars are significantly perturbed by the Sun.[3]

NotesEdit

Template:Notes

ReferencesEdit

  1. Cite error: Invalid <ref> tag; no text was provided for refs named Gazetteer
  2. Cite error: Invalid <ref> tag; no text was provided for refs named Smith_Soderblom_et_al._1986
  3. Cite error: Invalid <ref> tag; no text was provided for refs named Sheppard2005
  4. Template:Cite journal
  5. Cite error: Invalid <ref> tag; no text was provided for refs named Lassell1851
  6. Template:Cite journal
  7. Cite error: Invalid <ref> tag; no text was provided for refs named Lassell1851b
  8. Cite error: Invalid <ref> tag; no text was provided for refs named Kuiper_1949
  9. Template:Cite news
  10. Cite error: Invalid <ref> tag; no text was provided for refs named IAUC_7171
  11. Cite error: Invalid <ref> tag; no text was provided for refs named Karkoschka2001.2C_Voyager
  12. Cite error: Invalid <ref> tag; no text was provided for refs named Showalter_Lissauer_2006
  13. Cite error: Invalid <ref> tag; no text was provided for refs named IAUC_8217
  14. Cite error: Invalid <ref> tag; no text was provided for refs named Hughes1994
  15. Cite error: Invalid <ref> tag; no text was provided for refs named Denning1881
  16. Template:Cite journal
  17. Cite error: Invalid <ref> tag; no text was provided for refs named Thomas_1988
  18. Cite error: Invalid <ref> tag; no text was provided for refs named Esposito2002
  19. Cite error: Invalid <ref> tag; no text was provided for refs named Karkoschka2001.2C_Hubble
  20. Cite error: Invalid <ref> tag; no text was provided for refs named DumasSmithTerrile2003
  21. Cite error: Invalid <ref> tag; no text was provided for refs named Duncan_Lissauer_1997
  22. Cite error: Invalid <ref> tag; no text was provided for refs named Jacobson_Campbell_et_al._1992
  23. Cite error: Invalid <ref> tag; no text was provided for refs named Mousis_2004
  24. Template:Cite book
  25. Cite error: Invalid <ref> tag; no text was provided for refs named Hussmann_Sohl_et_al._2006
  26. Cite error: Invalid <ref> tag; no text was provided for refs named Grundy_Young_et_al._2006
  27. Cite error: Invalid <ref> tag; no text was provided for refs named Pappalardo1997
  28. Cite error: Invalid <ref> tag; no text was provided for refs named Tittemore_Wisdom_1990
  29. Cite error: Invalid <ref> tag; no text was provided for refs named Tittemore_1990
  30. Template:Cite journal
  31. Template:Cite journal
  32. Cite error: Invalid <ref> tag; no text was provided for refs named Widemann_Sicardy_et_al._2009
  33. Cite error: Invalid <ref> tag; no text was provided for refs named NSES
  34. Cite error: Invalid <ref> tag; no text was provided for refs named nssdc
  35. Cite error: Invalid <ref> tag; no text was provided for refs named Jacobson1998

External linksEdit

Template:Moons of Uranus

Template:Solar System moons (compact)

This page uses Creative Commons Licensed content from Wikipedia (view authors). Smallwikipedialogo.png
Community content is available under CC-BY-SA unless otherwise noted.