MOONS of URANUSUranus has presently twenty-seven (27) known moons (2006), which can be roughly divided into three groups; the five ‘classical’ main moons, the inner moons associated with the dark rings surrounding the planet, and those well quite some distance from the planet. Our knowledge about these satellites are limited by the single spacecraft visit by Voyager 2 in January 1986. On of the biggest problems is the slow changing tilt of the satellite orbital plane, which causes each little change in the aspects of the sun-lit portions visible to us. Many of the images obtained by Voyager 2 mean we only have knowledge of half the surface features. For us to see the opposing sides will require a future expedition to Uranus around 2016. However, no missions are planned at the moment. The Five Main Uranian MoonsThese five main moons are all smaller, at least when compared to largest moons of the other outer planets, but they are all in a similar range around 1 000 km. apiece. Each have classical names derived from the ancient world, while the other moons have names that have broken from the normal tradition, each adopted from characters in either the writings of Alexander Pope or the Shakespearian plays. Oberon is the outermost and brightest satellite that was discovered by Sir William Herschel in 11th January 1787, only six years after Uranus itself. He found the slightly fainter Titania on the same night. Oberon and Titania are very similar in size, being about 1 500 km. in diameter, with Titania being some 50 km larger. Although appearing quite similar, Oberon contains more slightly more ice, as seen in the 1.6 g.cm-3. density versus 1.72g.cm-3. Both are mixtures of ice and silicates, though about one-fifth the volume is likely made of methane or similar organic compounds frozen in the cold depths of the outer Solar System. Titania is generally darker but is scored by powdery white scratches from either meteor impacts or geological ice flows. Titania also has a deep canyon feature along its equator being similar to what is seen on Tethys — one of Saturn’s moons. Both Oberon and Titania, like the Earth’s are locked in to a synchronous orbit and always facing the same direction towards Uranus. Oberon and Titania remained for some years until William Lassell discovered the two closer moons of Umbriel and Ariel on 24 October 1851. Both of these moons are also similar in size. Umbriel is likely one of the dimmest and darkest place in the Solar System. The last of the traditional five moons was the smallest and closest to Uranus, Miranda, which was discovered by Gerard Kuiper in 1948. A 20cm telescope can see both Oberon and Titania when they are at maximum elongation from Uranus, whose magnitude at opposition can reach 13.7v and 13.9v magnitude, respectively. Both Umbriel and Ariel and are little more problematic, as they are closer to the planet and slightly fainter at 14.8v and 14.1v, respectively. These latter two moon can be seen with 30cm with care. Closest of all is Miranda, which is far too difficult for most amateur telescopes. The most interesting moon from the Voyager 2 flyby was Miranda with its very odd terrain. Twenty-seven satellites are now known to orbit the planet since 2006. URANUS SATELLITE TABLE**************************************************************** Distance Period Size No. Satellite (km) (days) (km) Discoverer Date **************************************************************** V Miranda 129 800 1.413 240x234x233 Kuiper 1948 I Ariel 191 000 2.520 581x578x579 Lassell 1851 II Umbriel 266 200 4.144 585 Lassell 1851 III Titania 435 800 8.706 789 Herschel 1787 VI Oberon 583 600 13.463 761 Herschel 1787 **************************************************************** VI Cordelia 49 752 0.335 13 Voyager 2 1986 VII Ophelia 53 764 0.376 16 Voyager 2 1986 VIII Bianca 59 165 0.435 27 Voyager 2 1986 IX Cressida 61 767 0.464 41 Voyager 2 1986 X Desdemona 62 659 0.474 35 Voyager 2 1986 XI Juliet 64 358 0.494 83 Voyager 2 1986 XII Portia 66 097 0.511 70 Voyager 2 1986 XIII Rosalind 69 927 0.558 36 Voyager 2 1986 XXVII Cupid 74 392 0.613 8.9 Showalter 2003 XIV Belinda 75 256 0.624 45 Voyager 2 1986 XXV Perdita 76 417 0.638 13 Karkoschka 1999 XV Puck 86 004 0.762 77 Voyager 2 1985 XXVI Mab 97 736 0.923 12.4 Showalter 2003 **************************************************************** XXII Francisco 4 276 000 266.6 6 Kavelaars 2003 XVI Caliban 7 231 000 579.7 40 Gladman 1997 XX Stephano 7 948 000 677.3 15 Gladman 1999 XXI Trinculo 8 578 000 759.0 5 Holman 2001 XVII Sycorax 12 213 000 1288d 95 Nicholson 1997 XXIII Margaret 14 345 000 1687d 5.5 Sheppard 2003 XVIII Prospero 16 243 000 1977d 15 Petit 1999 XIX Setebos 17 501 000 2235d 15 Kavelaars 1999 XXIV Ferdinand 20 901 000 2887d 6 Kavelaars 2001 **************************************************************** The Uranian RingsMany of the ring were first discovered in 1977 during an star occultation of the planet. Another was discovered by Voyager 2, followed by two outer rings in 2003. Presently there are twelve rings in total. There is strong evidence of interactions with the other moons, causing peaks or clumps, and even the so-called λ ring does not fully encircle the planet and appears in smaller clumps of orbiting material. Several are asociateed with so-called shepherd moons as seen with Sauturn. I.e. The ε ring seems to be shepherded by Cordelia and Ophelia. In 2003, based on the HST images the R2003 U2 ring was revealed to be controlled by the moons Portia and Rosalind. The newest, Mab, influences the R2003 U1 ring showing wave-like oscillations. Rings of Uranus************************** Distance Width Ring (km) (km) ************************** 1986U2R 38 000 2 500 6 41 840 1.5 5 42 230 c.2 4 42 580 c.2 α 44 720 4-10 β 45 670 5-11 η 47 190 1.6 γ 47 627 1-4 δ 48 290 3-8 λ 50 024 c.2 ε 51 140 20-96 R2003 U2 67 300 3 800 R2003 U1 97 700 17 000 ************************** Last Update : 23rd April 2018 Southern Astronomical Delights © (2018) For any problems with this Website or Document please e-mail me. |