Ariel (moon)
South polar region of Ariel in greyscale as imaged by Voyager 2 in January 1986. | |||||||||
| Discovery | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Discovered by | William Lassell | ||||||||
| Discovery date | 24 October 1851 | ||||||||
| Designations | |||||||||
Designation | Uranus I | ||||||||
| Pronunciation | /ˈɛəriəl/ or /ˈæriəl/ | ||||||||
| Adjectives | Arielian /æriˈiːliən/ | ||||||||
| Orbital characteristics | |||||||||
| Periapsis | 190670 km | ||||||||
| Apoapsis | 191129 km | ||||||||
| 190900 km | |||||||||
| Eccentricity | 0.0012 | ||||||||
| 2.520 d | |||||||||
Average orbital speed | 5.51 km/s | ||||||||
| Inclination | 0.260° (to Uranus's equator) | ||||||||
| Satellite of | Uranus | ||||||||
| Physical characteristics | |||||||||
| Dimensions | 1162.2 × 1155.8 × 1155.4 km | ||||||||
| 578.9±0.6 km (0.0908 Earths) | |||||||||
| 4211300 km2 | |||||||||
| Volume | 812600000 km3 | ||||||||
| Mass | (1.2331±0.0180)×1021 kg | ||||||||
Mean density | 1.517 g/cm3 (calculated) | ||||||||
| 0.246 m/s2 | |||||||||
| 0.533 km/s | |||||||||
| synchronous | |||||||||
| Albedo |
| ||||||||
| |||||||||
| 14.8 (R-band) | |||||||||
| 1.45 | |||||||||
Ariel is the fourth-largest moon of Uranus. Ariel orbits and rotates in Uranus's equatorial plane, which is almost perpendicular to the planet's orbit, giving the moon an extreme seasonal cycle.
It was discovered on 24 October 1851 by William Lassell and named for a character in two different pieces of literature. As of 2019, much of the detailed knowledge of Ariel derives from a single flyby of Uranus performed by the space probe Voyager 2 in 1986, which managed to image around 35% of the moon's surface. There are no active plans at present to return to study the moon in more detail, although various concepts such as a Uranus Orbiter and Probe have been proposed.
After Miranda, Ariel is the second-closest of Uranus's five major rounded satellites. Among the smallest of the Solar System's 19 known spherical moons (it ranks 14th among them in diameter), it is believed to be composed of roughly equal parts ice and rocky material. Its mass is approximately equal in magnitude to Earth's hydrosphere.
Like all of Uranus's moons, Ariel probably formed from an accretion disc that surrounded the planet shortly after its formation, and, like other large moons, it is likely differentiated, with an inner core of rock surrounded by a mantle of ice. Ariel has a complex surface consisting of extensive cratered terrain cross-cut by a system of scarps, canyons, grabens and ridges. The surface shows signs of more recent geological activity than other Uranian moons, most likely due to tidal heating.