Ariel
What is Ariel?
Moons· Diameter 1,158 km. The brightest of Uranus's moons and the one with the youngest surface — crisscrossed by canyons and smoothed by plains of flowed ice, evidence of a geologically active past. Find it orbiting outside Miranda in the orbit view.
📍 Visible from where you are right now — computed in your browser
bearing · altitude · rise time · best time tonight
The orbit of Ariel at this moment: https://nowsky.org/solar/orbit?fw=moon:uranus:ariel&sp=0.004 — replayed live, no login.
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
Frequently asked
- How big is Ariel?
- 1,158 km.
- How far is Ariel from Earth?
- 190,900 km.
- What is notable about Ariel?
- youngest, brightest surface; canyons and ice plains.
- Which planet does Ariel orbit?
- Uranus.
The vanished resonance that heated Ariel
Ariel's canyons and plains of flowed ice are the youngest surface among the Uranian moons, yet today's Ariel has no heat source for such activity — a moon this small loses its radioactive heat quickly, and it is in no orbital resonance with a neighbour. The favoured explanation is a resonance in the past: Ariel once shared a resonant orbit with Umbriel or Titania, and the tides of that time warmed the interior enough for ice to flow.
The Uranian moons have probably entered and left resonances repeatedly, because Uranus is not oblate enough to hold their orbits steady. Combining Webb's 2023 observations with ground-based spectra, carbon-dioxide and carbon-monoxide ices have been confirmed on Ariel, and an ocean beneath the ice has been proposed. Which moons hold oceans would be the first question for a Uranus orbiter.
The moon in depth
Ariel was discovered by William Lassell in 1851 along with Umbriel, and takes its name from the airy spirit in The Tempest. It is 1,158 km across, orbits 190,900 km from Uranus every 2.52 days, and reflects more light than any other Uranian moon. Its density, 1.66 times that of water, points to a roughly even mix of rock and ice.
The southern hemisphere Voyager 2 photographed shows few large craters and a comparatively young face. Canyons tens of kilometers wide form a network across it, their floors filled and smoothed by viscous ice that once flowed like glaciers. The likely cause was tidal heating during a past orbital resonance with Umbriel or Titania. In 2023 the James Webb telescope detected unexpectedly abundant carbon dioxide ice on the surface, strengthening the case for an ocean inside.
Follow Uranus in the orbit view to find Ariel just outside Miranda and inside Umbriel. If a Uranus orbiter mission flies, Ariel is among the first places it would check for an ocean beneath the ice.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.