Uranus' natural satellites

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Uranus has twenty-seven named moons. Five of them are massive enough to have achieved hydrostatic equilibrium and so would be considered dwarf planets if they were in orbit about the Sun. There are also thirteen inner moons that orbit within Uranus' ring system, and another nine outer irregular moons.

Major moons of Uranus compared, at their proper relative sizes.

The first two moons to be discovered, Titania and Oberon, were spotted by William Herschel on March 13, 1787. Two more, Ariel and Umbriel, were discovered by William Lassell in 1851. In 1852, Herschel's son John Herschel gave the four then-known moons their names. In 1948 Gerard Kuiper discovered the smallest moon out of the five, Miranda.

The flyby of the Voyager 2 space probe in January 1986 led to the discovery of a further 10 inner moons, and another satellite Perdita was later found after studying old Voyager photographs. Two more small inner moons were discovered by astronomers using the Hubble Space Telescope. Until 1997, Uranus was the only giant planet with no known irregular satellites. Since then, nine distant irregular moons have been identified using ground-based telescopes.

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. All the other moons together constitute only 0.1%, and are barely visible at this scale.
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. All the other moons together constitute only 0.1%, and are barely visible at this scale.

The region between the main rings and Miranda appears to be very crowded. The small moons there are constantly perturbed by each other. The system is chaotic and apparently unstable, and simulations show that the moons may perturb each other into crossing orbits which may result in collisions between the moons.[1][2] Desdemona may collide with either Cressida or Juliet within the next 100 million years.[3]

Unlike most planetary moons, which are named from antiquity, all the moons of Uranus are named after characters from the works of Shakespeare and Alexander Pope's work The Rape of the Lock.

Contents

The moons

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. Irregular (captured) moons with prograde orbits are shown in light grey, those with retrograde orbits in dark grey.

Notes: * Negative orbital periods indicate a retrograde orbit around Uranus (opposite to the planet's rotation).
Order Name (spheroidal moons in bold)

(Help:Pronunciation)

 Image Mean diameter (km) Mass (×1016 kg) Semi-major
axis (km)		 Orbital period (day) Inclination (°)
(to Uranus' equator)		 Discovery date
1 Uranus VI Cordelia kɔrˈdiːliə 42 ± 6 5.0? 49 751 0.335 034 0.084 79° 1986
2 Uranus VII Ophelia oʊˈfiːliə 46 ± 8 5.1? 53 764 0.376 400 0.103 6° 1986
3 Uranus VIII Bianca biːˈɑːŋkə 54 ± 4 9.2? 59 165 0.434 579 0.193° 1986
4 Uranus IX Cressida ˈkrɛsɨdə 82 ± 4 34? 61 766 0.463 570 0.006° 1986
5 Uranus X Desdemona ˌdɛzdɨˈmoʊnə 68 ± 8 23? 62 658 0.473 650 0.111 25° 1986
6 Uranus XI Juliet ˈdʒuːliət 106 ± 8 82? 64 360 0.493 065 0.065° 1986
7 Uranus XII Portia ˈpɔrʃiə 140 ± 8 170? 66 097 0.513 196 0.059° 1986
8 Uranus XIII Rosalind ˈrɒzəlɨnd 72 ± 12 25? 69 927 0.558 460 0.279° 1986
9 Uranus XXVII Cupid ˈkjuːpɨd ~ 18 0.38? 74 800 0.618 0.1° 2003
10 Uranus XIV Belinda bɨˈlɪndə
90 ± 16 49? 75 255 0.623 527 0.031° 1986
11 Uranus XXV Perdita ˈpɝdɨtə 30 ± 6 1.8? 76 420 0.638 0.0° 1986
12 Uranus XV Puck ˈpʌk
162 ± 4 290? 86 004 0.761 833 0.319 2° 1985
13 Uranus XXVI Mab ˈmæb ~ 25 1.0? 97 734 0.923 0.1335° 2003
14 Uranus V Miranda mɨˈrændə
471.6 ± 1.4 6 600 ± 700 129 390 1.413 479 4.232° 1948
15 Uranus I Ariel ˈɛəriəl
1157.8 ± 1.2 135 000 ± 12 000 191 020 2.520 379 0.260° 1851
16 Uranus II Umbriel ˈʌmbriəl
1169.4 ± 5.6 117 000 ± 13 000 266 300 4.144177 0.205° 1851
17 Uranus III Titania tɨˈtɑːnjə
1577.8 ± 3.6 353 000 ± 9 000 435 910 8.705 872 0.340° 1787
18 Uranus IV Oberon ˈoʊbərɒn
1522.8 ± 5.2 301 000 ± 7 000 583 520 13.463 239 0.058° 1787
19 Uranus XXII Francisco frænˈsɪskoʊ ~ 22 0.72? 4 276 000 -266.56* 147.459° 2001
20 Uranus XVI Caliban ˈkælɨbæn ~ 72 25? 7 231 000 -579.73* 139.885° 1997
21 Uranus XX Stephano ˈstɛfənoʊ ~ 32 2.2? 8 004 000 -677.37* 141.873° 1999
22 Uranus XXI Trinculo ˈtrɪŋkjʊloʊ ~ 18 0.39? 8 504 000 -749.24* 166.252° 2001
23 Uranus XVII Sycorax ˈsɪkəræks ~ 150 230? 12 179 000 -1288.28* 152.456° 1997
24 Uranus XXIII Margaret ˈmɑrgərɨt ~ 20 0.54? 14 345 000 +1687.01 51.455° 2003
25 Uranus XVIII Prospero ˈprɒspəroʊ ~ 50 8.5? 16 256 000 -1978.29* 146.017° 1999
26 Uranus XIX Setebos ˈsɛtɨbʌs ~ 48 7.5? 17 418 000 -2225.21* 145.883° 1999
27 Uranus XXIV Ferdinand ˈfɝdɨnænd ~ 20 0.54? 20 901 000 -2887.21* 167.346° 2001

Sources: NASA/NSSDC, University of Hawaii and Natural Satellites Ephemeris Service (for the outer satellites). These sources give no information on the masses for the small satellites.

Irregular moons

Irregular satellites of Uranus.
Irregular satellites of Uranus.

The diagram illustrates the orbits of the irregular moons of Uranus discovered so far. The eccentricity of the orbits is represented by the yellow segments (extending from the pericentre to the apocentre) with the inclination represented on Y axis. The satellites above the axis are prograde, the satellites beneath are retrograde. The X axis is labelled in Gm (million km) and the fraction of the Hill sphere's (gravitational influence) radius (approximately 70 million km for Uranus).

Unlike for Jupiter's irregulars, no correlation axis versus inclination can be found among the known population. Instead, the retrograde moons can be divided into two groups based on axis/eccentricity. The inner group includes satellites closer to Uranus (a < 0.15 rH) and moderately eccentric (~0.2), namely: Francisco, Caliban, Stephano and Trinculo. The outer group (a > 0.15 rH) includes satellites with high eccentricity (~0.5): Sycorax, Prospero, Setebos and Ferdinand.[4]

Naming notes

The sources of the names are the following works:

Some asteroids share the same names as moons of Uranus: 171 Ophelia, 218 Bianca, 593 Titania, 666 Desdemona, 763 Cupido and 2758 Cordelia. See also Name conflicts of solar system objects.

Spurious moons

Titania and Oberon were discovered by Herschel on January 11, 1787. Subsequently, Herschel observed, or believed that he observed, four other moons, two in 1790 (January 18 and February 9) and two more in 1794 (February 28 and March 26). 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. It was therefore concluded that Herschel's four satellites were spurious, probably arising from the misidentification of small stars in the vicinity of Uranus as satellites, and the credit for the discovery of Ariel and Umbriel was given to Lassell.[5] 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 and 107.69 days (exterior to Oberon).[6]

References

  1. ^ Showalter, Mark R.; Lissauer, Jack J. (2005-12-22). "The Second Ring-Moon System of Uranus: Discovery and Dynamics". Science Express 311: 973. doi:10.1126/science.1122882. PMID 16373533. 
  2. ^ Laura Layton (December 28, 2005). "Uranus' second ring-moon system". Astronomy Magazine. Retrieved on 2008-05-10.
  3. ^ Duncan, Martin J.; Jack J. Lissauer (1997). "Orbital Stability of the Uranian Satellite System". Icarus 125 (1): 1–12. doi:10.1006/icar.1996.5568. Retrieved on 2008-05-10. 
  4. ^ Scott S. Sheppard, David C. Jewitt, and Jan Kleyna An Ultradeep Survey for Irregular Satellites of Uranus: Limits to Completeness, The Astronomical Journal, 129 (2005), pages 518–525 (preprint)
  5. ^ Scientific American Supplement, No. 303, October 22, 1881 / Various
  6. ^ 1994QJRAS..35..331H Page 334

External links

Moons of Uranus
Generally listed in increasing distance from Uranus
Inner
Cordelia · Ophelia · Bianca · Cressida · Desdemona · Juliet · Portia · Rosalind · Cupid  · Belinda · Perdita · Puck · Mab
Major (spheroid)
Outer (irregular)
Characteristics
Rings of Uranus
Uranus
Major moons Photograph of Uranus taken by Voyager 2
Characteristics
Atmosphere · Climate · Rings · Moons
Discovery
Exploration
Other
Natural satellites of the Solar System
Planetary satellites
Terrestrial · Martian · Jovian · Saturnian · Uranian · Neptunian
 Rhea, Saturn's second-largest moon
Other satellite systems
Largest satellites
Ganymede · Titan · Callisto · Io · Moon · Europa · Triton
Titania · Rhea · Oberon · Iapetus · Charon · Umbriel · Ariel · Dione · Tethys  · Enceladus · Miranda · Proteus · Mimas
Inner satellites · Trojans · Irregulars · List · List by diameter · Timeline of discovery · Naming
The Solar System
The Sun Mercury Venus The Moon Earth Phobos and Deimos Mars Ceres The asteroid belt Jupiter Moons of Jupiter Saturn Moons of Saturn Uranus Moons of Uranus Moons of Neptune Neptune Moons of Pluto Pluto Moons of Haumea Haumea Makemake The Kuiper Belt Dysnomia Eris The Scattered Disc The Oort Cloud
See also astronomical objects, the Solar System's list of objects, sorted by radius or mass, and the Solar System Portal
Retrieved from "http://en.wikipedia.org/wiki/Moons_of_Uranus"

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