|Discovered by||William Lassell|
|Discovered in||October 24, 1851|
|Semi-major axis||266,000 km|
|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 moon of||Uranus|
|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 velocity||36.94 km/h (at the equator)|
|Albedo||0.21 ± 0.02|
|Angular size||0.093" (max)|
|Atmospheric pressure||0 kPa|
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]
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.
Other websites [change]
- 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
- Yeomans, Donald K. (2006-Jul-13). "Planetary Satellite Physical Parameters". JPL Solar System Dynamics. http://ssd.jpl.nasa.gov/?sat_phys_par. Retrieved 2005-06-12.
- "Classic Satellites of the Solar System". Observatorio ARVAL. http://www.oarval.org/ClasSaten.htm. Retrieved 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. 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.