Umbriel (moon)
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| Discovery | |||||||
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| Discovered by | William Lassell | ||||||
| Discovered in | October 24, 1851 | ||||||
| Orbital characteristics | |||||||
| Semi-major axis | 266,000 km | ||||||
| Eccentricity | 0.0039 | ||||||
| Periastron (Periuranion) | 265,000 km | ||||||
| Apastron (Apuranion) | 267,000 km | ||||||
| Orbital circumference | 1,671,000 km | ||||||
| Orbital period | 4.144 d | ||||||
| Mean orbital speed | 4.668 km/s | ||||||
| Minimum orbital speed | 4.650 km/s | ||||||
| Maximum orbital speed | 4.686 km/s | ||||||
| Inclination | 0.205° (to Uranus' equator) | ||||||
| Is a satellite of | Uranus | ||||||
| Physical characteristics[1] | |||||||
| Mean diameter | 1169.4 km (0.092 Earths) | ||||||
| Surface area | 4,296,000 km2 (0.008 Earths) | ||||||
| Volume | 837,300,000 km3 (0.0008 Earths) | ||||||
| Mass | 1.2±0.1×1021 kg (0.0002 Earths) | ||||||
| Mean density | 1.40±0.16 g/cm3 | ||||||
| Surface gravity | 0.23 m/s2 (0.023 g) | ||||||
| Escape velocity | 0.52 km/s | ||||||
| Rotation period | synchronous | ||||||
| Axial tilt | zero | ||||||
| Rotation velocity | 36.94 km/h (at the equator) | ||||||
| Albedo | 0.21 ± 0.02[1] | ||||||
| Apparent Magnitude | 14.81[2] | ||||||
| Angular Size | 0.093" (max) | ||||||
| Surface temp. |
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| Atmospheric pressure | 0 kPa | ||||||
Umbriel (pronounced /ˈʌmbriəl/ um'-bree-əl) is a moon of Uranus discovered on October 24, 1851 by William Lassell. It was discovered at the same time as Ariel.
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[edit] Name
The name "Umbriel" and the names of all four satellites of Uranus then known were suggested by John Herschel in 1852 at the request of Lassell.[3] Lassell had earlier endorsed Herschel's 1847 naming scheme for the seven then-known satellites of Saturn and had named his newly-discovered eighth satellite Hyperion in accordance with Herschel's naming scheme in 1848. Umbriel is the 'dusky melancholy sprite' in Alexander Pope's The Rape of the Lock, and the name suggests the Latin umbra, shadow. The adjectival form of the name is Umbrielian.
It is also designated Uranus II.
[edit] Physical characteristics
So far the only close-up images of Umbriel are from the Voyager 2 probe, which made observations of the moon during its Uranus flyby in January, 1986. During the flyby the southern hemisphere of the moon was pointed towards the Sun so only it was studied.
Umbriel's surface is the darkest of the Uranian moons, and reflects only about half as much light as Ariel, Uranus' brightest satellite. Umbriel's heavily cratered surface has probably been stable since the Late Heavy Bombardment. It has far more and larger craters than do Ariel and Titania and is also the least geologically active.[4] It is mostly composed of water ice, with the balance made up of silicate rock, and other ices such as methane. Methane can break down and form reddish-black organic compounds such as tholins when bombarded by high-energy particles.[5] Near-IR spectra of Ariel and Umbriel clearly show that water ice dominates the spectra of these objects.[6]
Umbriel's most prominent feature is Wunda, a large ring of bright material near Umbriel's equator (see picture; the viewpoint is nearly polar). Wunda is presumably some kind of crater, but its exact nature is mysterious. Nearby, seen along the terminator, is the crater Skynd, which lacks a bright rim but possesses a bright central peak.
[edit] See also
[edit] External links
- Umbriel Profile by NASA's Solar System Exploration
- William Lassell, Astronomical Journal 2 (1851) 70
- AN, 33 (1852) 257/258
- AN, 34 (1852) 325/326
- Uranus and moons as seen by the VLT in August 2007
[edit] References
- ^ a b Yeomans, Donald K. (2006-Jul-13). Planetary Satellite Physical Parameters. JPL Solar System Dynamics. Retrieved on 2005-06-12.
- ^ Classic Satellites of the Solar System. Observatorio ARVAL. Retrieved on 2007-09-28.
- ^ http://adsabs.harvard.edu//full/seri/AN.../0034//0000169.000.html Adsabs.harvard.edu Retrieved on 06-01-07
- ^ Arnett, William A. (2006 Aug 25). Umbriel. The Nine Planets. Retrieved on 2007-11-09.
- ^ Overbye, Roger (April 1986). Voyager was on target again; in the latest unmanned triumph, Voyager 2 surveyed Uranus and sent back a real bull's-eye. Discover. Retrieved on 2007-11-09.
- ^ Dumas, Christophe; Bradford A. Smith, and Richard J. Terrile (2003). "Hubble Space Telescope NICMOS Multiband Photometry of Proteus and Puck". The Astronomical Journal 126 (2003): 1080–1085. doi:.
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