Ariel
What is Ariel?
Moons· Diameter 1,158 km. The brightest moon of Uranus and the one with the youngest surface, crossed by canyons and smoothed by plains of flowed ice — signs of an active past.
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Orbit and size
| Diameter | 1,158 km |
|---|---|
| Distance from Uranus | 190,900 km |
| Orbit | 2.52 d |
| Note | youngest, brightest surface; canyons and ice plains |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Parent planet and sibling moons
The lost resonance that once warmed Ariel
Ariel's canyons and ice plains are the youngest ground on any moon of Uranus, yet today Ariel has no heat source to drive such activity. It is small, so the heat it had at birth escaped quickly, and it is not now moving in step with any neighbouring moon. Where the heat that softened its ice came from is therefore a puzzle.
Scientists look for the answer in the past. Ariel may once have orbited in step with a neighbouring moon. When that happens, the moons' gravity regularly stretches each other's orbits out of round. On a stretched orbit, Uranus's pull squeezes and relaxes Ariel over and over, and the friction heats its interior. Because Uranus is less flattened than Jupiter or Saturn, its moons are thought to have slipped into and out of such orbits fairly easily.
In July 2006 the Hubble Space Telescope caught a rare sight: Ariel passing in front of Uranus and casting its shadow on the cloud tops. Because Uranus is tipped on its side, such events cannot be seen at just any time. They happen only in the few years around each equinox, which comes about every 42 years, when the moons' orbits are seen edge-on from Earth.
The moon in depth
Ariel was discovered in 1851 by the English astronomer William Lassell, along with Umbriel. It is named after the spirit of the air in The Tempest. It is 1,158 km across and orbits 190,900 km from Uranus, going around once every 2.52 days. It reflects sunlight better than any other moon of Uranus, so it is the brightest. With a density about 1.5 times that of water, it seems to be roughly half ice and half rock.
The surface photographed by Voyager 2 has few large craters, which means it was reshaped fairly recently. Instead, canyons tens of kilometres wide form a network across it. Their floors were filled and smoothed by thick, slow-moving ice that flowed in. This shows that Ariel was once warm enough inside for ice to move.
Follow Uranus in the orbit view to find Ariel just outside Miranda and inside Umbriel. Recently the James Webb Space Telescope found more carbon dioxide ice on Ariel's surface than expected. Some scientists think it may have come up from an ocean beneath the ice. This idea has not yet been confirmed.
Frequently asked
- How big is Ariel?
- The diameter of Ariel is 1,158 km.
- How far is Ariel from Earth?
- The distance from uranus of Ariel is 190,900 km.
- What is notable about Ariel?
- The note of Ariel is youngest, brightest surface; canyons and ice plains.
- Which planet does Ariel orbit?
- Ariel orbits Uranus.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.