Moons of Uranus
From Wikipedia, the free encyclopedia
The seventh planet of the Solar System Uranus has twenty-seven moons.[1] The first two of them—Titania and Oberon were discovered in 1787 by William Herschel, while the last two were spotted in 2005 by the Hubble Space Telescope.[2] The moons of Uranus are named after the various characters from from the works of William Shakespeare and Alexander Pope.[3]
Uranian moons are divided into three groups: 13 inner moons, five major moons and nine irregular moons. The inner moons are dark small bodies that share common properties and the origin with the rings of Uranus. The five major moons are massive enough to have achieved hydrostatic equilibrium. Four of them show signs of endogenic resurfacing and tectonics.[4] The irregular moons orbit at the large distance from Uranus. All of them have elliptic and strongly inclined (even retrograde) orbits.[1]
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[edit] Discovery
The first two moons to be discovered, Titania and Oberon, were spotted by William Herschel on March 13, 1787. Two more moons, Ariel and Umbriel, were discovered by William Lassell in 1851.[5] In 1852, Herschel's son John Herschel gave the four then-known moons their names.[6] In 1948 Gerard Kuiper discovered the smallest one out of the five largest moons, Miranda.[6]
The flyby of the Voyager 2 space probe in January 1986 led to the discovery of a further 10 inner moons,[4] and another satellite Perdita was in 2001 found after studying old Voyager photographs.[7] Two more small inner moons (Cupid and Mab) were discovered by astronomers using the Hubble Space Telescope in 2005.[2] 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.[1]
[edit] Names
- See also: Name conflicts of solar system objects
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:[3]
- The Rape of the Lock, poem by Alexander Pope — Ariel, Umbriel, Belinda
- Plays by William Shakespeare:
- A Midsummer Night's Dream: Titania, Oberon, Puck
- The Tempest: (Ariel), Miranda, Caliban, Sycorax, Prospero, Setebos, Stephano, Trinculo, Francisco, Ferdinand
- King Lear: Cordelia
- Hamlet: Ophelia
- The Taming of the Shrew: Bianca
- Troilus and Cressida: Cressida
- Othello: Desdemona
- Romeo and Juliet: Juliet, Mab
- The Merchant of Venice: Portia
- As You Like It: Rosalind
- Much Ado About Nothing: Margaret
- The Winter's Tale: Perdita
- Timon of Athens: Cupid
Some asteroids share the same names as moons of Uranus: 171 Ophelia, 218 Bianca, 593 Titania, 666 Desdemona, 763 Cupido and 2758 Cordelia.
[edit] Characteristics and groups
[edit] Inner moons
- See also: Rings of Uranus
As of 2008 13 inner moons of Uranus are known.[2] Their orbits lie inside that of Miranda. All inner moons are intimately connected to the Rings of Uranus, which are probably resulted from fragmentation of one or several small inner moons. Two innermost moons (Cordelia and Ophelia) serve as shepherds of the ε ring of Uranus, while small moon Mab is a source of the outermost Uranian μ ring.[2] Puck circles the planet between the orbits of Mab and Perdita and appears to be a transition object between inner moons and the large Uranian satellites. All inner moons are dark objects with geometrical albedo not exceeding 10%.[8] They are made of water ice contaminated with some dark material—probably radiation processed organics.
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.[2][9] Desdemona may collide with either Cressida or Juliet within the next 100 million years.[10]
[edit] Major moons
Uranus has five major moons: Miranda, Ariel, Umbriel, Titania and Oberon. The range in diameter from around 500 km for Miranda to about 1600 km for Titania.[11] All large moons are relatively dark objects: their geometrical albedo varies in the range 30–50%, while bond albedo varies in the range 10–23%.[8] Umbriel is the darkest moon and Ariel is the brightest one. The masses of the moons are from 6 × 1019 kg (Miranda) to 3.5 × 1021 kg (Titania).[11] All these moons (except Miranda, which is made primarily from ice) are made from approximately equal amounts of rocks and ice.[12] Their surfaces are heavily cratered, though all of them except Umbriel show signs of endogenic resurfacing in the form of lineaments (canyons) and ovoid structures (corona) in the case of Miranda.[4] Uranian moons (except Miranda) may be differentiated with rocky core in the center surrounded by ice mantle.[12] Titania and Oberon may harbor a layer of liquid water (ocean) at the core/mantle boundary.[12]
[edit] Irregular moons
As of 2005 Uranus has nine known irregular moons, which circle the planet at the distance much greater than that of Oberon—the furthest of the large moons. 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).[1]
Irregular moons of Uranus range in size from about 150 km (Sycorax) to 20 km (Margaret).[1] 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.[1] The outer group (a > 0.15 rH) includes satellites with high eccentricity (~0.5): Sycorax, Prospero, Setebos and Ferdinand.[1]
[edit] 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.[13] 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).[14]
[edit] Table
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.
| Order | Name (spheroidal moons in bold) |
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 | 40.2 ± 6 | 4.4? | 49 751 | 0.335 034 | 0.084 79° | 1986 | |
| 2 | Uranus VII | Ophelia | oʊˈfiːliə | 42.8 ± 8 | 5.3? | 53 764 | 0.376 400 | 0.103 6° | 1986 | |
| 3 | Uranus VIII | Bianca | biːˈɑːŋkə | 51.4 ± 4 | 9.2? | 59 165 | 0.434 579 | 0.193° | 1986 | |
| 4 | Uranus IX | Cressida | ˈkrɛsɨdə | 79.6 ± 4 | 34? | 61 766 | 0.463 570 | 0.006° | 1986 | |
| 5 | Uranus X | Desdemona | ˌdɛzdɨˈmoʊnə | 64.0 ± 8 | 18? | 62 658 | 0.473 650 | 0.111 25° | 1986 | |
| 6 | Uranus XI | Juliet | ˈdʒuːliət | 93.6 ± 8 | 56? | 64 360 | 0.493 065 | 0.065° | 1986 | |
| 7 | Uranus XII | Portia | ˈpɔrʃiə | 135.2 ± 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 | ± 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 |
.jpg) |
1157.8 ± 1.2 | 135 000 ± 12 000 | 191 020 | 2.520 379 | 0.260° | 1851 |
| 16 | Uranus II | Umbriel | ˈʌmbriəl |
.jpg) |
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, Scott Sheppard and Natural Satellites Ephemeris Service (for the outer satellites). These sources give no information on the masses for the small satellites.
[edit] References
- ^ a b c d e f g h Sheppard, Scott S.; Jewitt, David and Kleyna, Jan (2005). "An ultradeep survey for irregular satellites of uranus: Limits to completeness". The Astronomical Journal 129: 518–525. doi:. http://adsabs.harvard.edu/abs/2005AJ....129..518S.
- ^ a b c d e f Showalter, Mark R.; Lissauer, Jack J. (2006). "The Second Ring-Moon System of Uranus: Discovery and Dynamics". Science 311: 973–977. doi:. PMID 16373533. http://adsabs.harvard.edu/abs/2006Sci...311..973S.
- ^ a b c "Planet and Satellite Names and Discoverers". Gazetteer of Planetary Nomenclature. USGS Astrogeology (July 21 2006). Retrieved on 2006-08-06.
- ^ a b c d Smith, B.A.; Soderblom, L.A.; Beebe, A. et al. (1986). "Voyager 2 in the Uranian System: Imaging Science Results". Science 233: 97–102. doi:. PMID 17812889. http://adsabs.harvard.edu/abs/1986Sci...233...43S.
- ^ a b Lassell, W. (1851). "On the interior satellites of Uranus". Monthly Notices of the Royal Astronomical Society 12: 15–17. http://adsabs.harvard.edu/abs/1851MNRAS..12...15L.
- ^ a b c Kuiper, Gerard P. (1949). "The Fifth Satellite of Uranus". Publications of the Astronomical Society of the Pacific 61 (360): 129. doi:. http://adsabs.harvard.edu/abs/1949PASP...61..129K.
- ^ a b Karkoschka, Erich (2001). "Voyager's Eleventh Discovery of a Satellite of Uranus and Photometry and the First Size Measurements of Nine Satellites". Icarus 151: 69–77. doi:. http://adsabs.harvard.edu/abs/2001Icar..151...69K.
- ^ a b c Karkoschka, Erich (2001). "Comprehensive Photometry of the Rings and 16 Satellites of Uranus with the Hubble Space Telescope". Icarus 151: 51–68. doi:. http://adsabs.harvard.edu/abs/2001Icar..151...51K.
- ^ Laura Layton (December 28, 2005). "Uranus' second ring-moon system". Astronomy Magazine. Retrieved on 2008-05-10.
- ^ Duncan, Martin J.; Jack J. Lissauer (1997). "Orbital Stability of the Uranian Satellite System". Icarus 125 (1): 1–12. doi:.
- ^ a b c Jacobson, R.A.; Campbell, J.K.; Taylor, A.H. and Synnott, S.P. (1992). "The masses of Uranus and its major satellites from Voyager tracking data and Earth based Uranian satellite data". The Astronomical Journal 103 (6): 2068–78. doi:. http://adsabs.harvard.edu/abs/1992AJ....103.2068J.
- ^ a b c d Hussmann, Hauke; Sohl, Frank; Spohn, Tilman (2006). "Subsurface oceans and deep interiors of medium-sized outer planet satellites and large trans-neptunian objects". Icarus 185: 258–273. doi:. http://adsabs.harvard.edu/abs/2006Icar..185..258H.
- ^ Scientific American Supplement, No. 303, October 22, 1881 / Various
- ^ 1994QJRAS..35..331H Page 334
[edit] External links
- Uranus' Moons by NASA's Solar System Exploration
- NASA's Hubble Discovers New Rings and Moons Around Uranus (STScI-2005-33, December 22, 2005)
- Ring diagram (Courtesy of Astronomy Magazine 2005)
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