Ariel (moon)

Ariel (moon)

Infobox Planet
name = Ariel
alt_names = Uranus I
adjectives = Arielian

caption = Click image for description
bgcolour = #a0ffa0
discovery = yes
discoverer = William Lassell
discovered = October 24, 1851
semimajor = 191,020 km
mean_orbit_radius = 190,900 km
eccentricity = 0.0012
period = 2.520 d
inclination = 0.260° (to Uranus' equator)
satellite_of = Uranus
physical_characteristics = yes
mean_radius = 578.9 km (0.0908 Earths)
dimensions = 1162.2 × 1155.8 × 1155.4 km
surface_area = 4,211,300 km²
volume = 812,600,000 km³
mass = 1.35e|21 kg (2.26e|-4 Earths)
density = 1.67 g/cm³
surface_grav = 0.27 m/s2
escape_velocity = 0.56 km/s
rotation = synchronous
albedo = 0.39
magnitude = 14.16 cite web|title=Classic Satellites of the Solar System|url=|publisher=Observatorio ARVAL|accessdate=2007-09-28]
single_temperature = ~58 K

Ariel (pronEng|ˈɛəriəl respell|AIR|ee-əl) is a moon of Uranus discovered on 24 October 1851 by William Lassell. It was discovered at the same time as Umbriel.


Ariel is named after the leading sylph in Alexander Pope's poem "The Rape of the Lock". It is also the name of the spirit who serves Prospero in Shakespeare's "The Tempest".

The name "Ariel" and the names of all four satellites of Uranus then known were suggested by John Herschel in 1852 at the request of Lassell. [ [] "" Retrieved on 06-01-07 ] 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. The adjectival form of the name is "Arielian".

It is also designated Uranus I.

Physical characteristics

The first and so far only close-up observations of Ariel were made by the "Voyager 2" probe during its 1986 Uranus fly-by. "Voyager 2" made its closest approach of Ariel on January 24, 1986 and passed within 127 000 km of the moon. [ Voyager Mission Description] . Accessed May 29, 2006] Because the moon's south pole was pointed towards the Sun, only the southern hemisphere was photographed.

Ariel's composition is roughly 70% ices (water ice, carbon dioxide ice, and possibly methane ices) and 30% silicate rock, and it appears to have regions of fresh frost in places, particularly in the ejecta radiating from young impact craters. The oldest and most extensive geologic unit observed on Ariel by "Voyager 2" was a vast area of cratered plains centered near Ariel's south pole. Analysis of craters seen on Ariel's cratered plains suggest most are younger than many of those seen on Titania, Oberon, and Umbriel.B. A. Smith et al. (1982). " [ Voyager 2 in the Uranian system - Imaging science results] ". "Science" 233: 43-64.] The largest crater observed on Ariel is Yangoor, at only 78 km across, and shows signs of deformation since its formation. "Voyager 2" also observed a network of faults, canyons, and icy outflows running along Ariel's mid-southern latitudes, breaking up the cratered plains region. The canyons probably represent grabens formed by extensional faulting. Smooth material and grooves are often seen running down length of Ariel's valley networks, suggested that some canyon floors have been covered in warm ice extruded from Ariel's interior.

Ariel's past geologic activity is believed to have been driven by tidal heating at a time when its orbit was more eccentric than currently. Early in its history, Ariel was apparently captured in a 4:1 orbital resonance with Titania, from which it subsequently escaped. [cite journal
title= Tidal Heating of Ariel
author= W. C. Tittemore
journal= Icarus
volume= 87
pages= 110–139
year= 1990
doi= 10.1016/0019-1035(90)90024-4
] The resonance would have increased orbital eccentricity; resulting tidal friction due to time-varying tidal forces from Uranus would have caused warming of the moon's interior. In the Uranus system, due to the planet's lesser degree of oblateness, and the larger relative size of its satellites, escape from a mean motion resonance is much easier than for satellites of Jupiter or Saturn.

Official names have been given to the following geological feature types on Ariel:
* Craters
* Chasmata (chasms)
* Valles (valleys)

Ariel may be like Saturn's Dione. They are very similar in size, density and mass with Ariel only having slightly higher numbers. Both appear to have had past geological activity.


* On July 26, 2006, the Hubble Space Telescope captured a rare transit made by Ariel across the face of Uranus, during which the satellite cast a shadow that could be seen on the Uranian cloudtops. Such events are rare and only occur around equinoxes, as the moon's orbital plane about Uranus is tilted 98° to Uranus's orbital plane about the Sun.cite web
title=Uranus and Ariel
publisher=Hubblesite (News Release 72 of 674)
* During Uranus' equinox (December 2007) Ariel was producing eclipses across the center of Uranus. [cite web
date = 2007-December-10 01:48 UT
title = Eclipse of the Sun by Ariel from the center of Uranus during equinox
publisher = [ JPL Solar System Simulator]
url =
accessdate = 2008-06-07

ee also

* List of geological features on Ariel

Notes and references

External links

* [ Ariel Profile] by [ NASA's Solar System Exploration]
* [ William Lassell, "Astronomical Journal" 2 (1851) 70]
* [ AN, 33 (1852) 257/258]
* [ AN, 34 (1852) 325/326]
* [ Ariel basemap derived from Voyager images]
* [ NASA Archive of publically released Ariel images]


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