Umbriel as seen by Voyager 2 in 1986
|Discovered by||William Lassell|
|Discovery date||October 24, 1851|
|Alternative names||Uranus II|
|Semi-major axis||266 000 km|
|Orbital period||4.144 d|
|Inclination||0.128° (to Uranus's equator)|
|Mean radius||584.7 ± 2.8 km (0.092 Earths)|
|Surface area||4 296 000 km2 (0.008 Earths)[a]|
|Volume||837 300 000 km3 (0.0008 Earths)[b]|
|Mass||1.172 ± 0.135 × 1021 kg (2 × 10−4 Earths)|
|Mean density||1.39 ± 0.16 g/cm3|
|Equatorial surface gravity||0.2 m/s2 (~ 0.023 g)[c]|
|Escape velocity||0.52 km/s[d]|
|Rotation period||presumed synchronous|
|Apparent magnitude||14.5 (V-band, opposition)|
Name[change | edit source]
The name "Umbriel" and the names of all four moons of Uranus then known were suggested by John Herschel in 1852 at the request of Lassell. Lassell had earlier supported Herschel's 1847 naming scheme for the seven then-known moons of Saturn and had named his newly-found eighth moon 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.
Physical characteristics[change | edit source]
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 moon. It has far more and bigger craters than do Ariel and Titania and is also the least geologically active. It is mostly made 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. Near-IR spectra of Ariel and Umbriel clearly show that water ice dominates the spectra of these objects.
Craters[change | edit source]
Craters on Umbriel are named after many different demons from various mythologies.
|Malingee||Malingee (Australian Aboriginal mythology)|
|Minepa||Minepa (Makua people of Mozambique)|
|Wokolo||Wokolo (Bambara people of West Africa)|
|Wunda||Wunda (Australian Aboriginal mythology)|
Other websites[change | edit source]
- 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
Notes[change | edit source]
References[change | edit source]
- "Umbriel". Dictionary.com. http://dictionary.reference.com/browse/Umbriel. Retrieved 2010-01-14.
- "Planetary Satellite Mean Orbital Parameters". Jet Propulsion Laboratory, California Institute of Technology. http://ssd.jpl.nasa.gov/?sat_elem.
- Thomas, P. C. (1988). "Radii, shapes, and topography of the satellites of Uranus from limb coordinates". Icarus 73 (3): 427–441. doi:10.1016/0019-1035(88)90054-1. http://adsabs.harvard.edu/abs/1988Icar...73..427T.
- Jacobson, R. A.; Campbell, J. K.; Taylor, A. H.; Synnott, S. P. (June 1992). "The masses of Uranus and its major satellites from Voyager tracking data and earth-based Uranian satellite data". The Astronomical Journal 103 (6): 2068–2078. doi:10.1086/116211. http://adsabs.harvard.edu/abs/1992AJ....103.2068J.
- Smith, B. A.; Soderblom, L. A.; Beebe, A.; Bliss, D.; Boyce, J. M.; Brahic, A.; Briggs, G. A.; Brown, R. H. et al. (4 July 1986). "Voyager 2 in the Uranian System: Imaging Science Results". Science 233 (4759): 43–64. doi:10.1126/science.233.4759.43. PMID 17812889. http://adsabs.harvard.edu/abs/1986Sci...233...43S.
- Karkoschka, Erich (2001). "Comprehensive Photometry of the Rings and 16 Satellites of Uranus with the Hubble Space Telescope". Icarus 151 (1): 51–68. doi:10.1006/icar.2001.6596. http://adsabs.harvard.edu/abs/2001Icar..151...51K.
- "Planetary Satellite Physical Parameters". NASA/JPL. http://ssd.jpl.nasa.gov/?sat_phys_par. Retrieved June 6, 2010.
- Grundy, W. M.; Young, L. A.; Spencer, J. R.; Johnson, R. E.; Young, E. F.; Buie, M. W. (October 2006). "Distributions of H2O and CO2 ices on Ariel, Umbriel, Titania, and Oberon from IRTF/SpeX observations". Icarus 184 (2): 543–555. doi:10.1016/j.icarus.2006.04.016. http://adsabs.harvard.edu/abs/2006Icar..184..543G.
- (German) Beobachtungen der Uranus-Satelliten Adsabs.harvard.edu Retrieved on 06-01-07
- Arnett, William A. (2006 Aug 25). "Umbriel". The Nine Planets. http://www.nineplanets.org/umbriel.html. Retrieved 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. http://findarticles.com/p/articles/mi_m1511/is_v7/ai_5083814/pg_7. Retrieved 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:10.1086/375909. http://www.journals.uchicago.edu/cgi-bin/resolve?id=doi:10.1086/375909.