Ariel is the brightest of Uranus’ major moons, its surface cut by broad rift valleys whose floors look smooth and freshly paved. It has fewer large craters than its siblings - the mark of the youngest surface among the five, resurfaced long after the moon formed.
Its name fits both naming traditions: Ariel is a sprite in Shakespeare’s The Tempest and in Pope’s The Rape of the Lock - all Uranian moons are named for characters from those authors.
It reflects about 39% of incoming sunlight - the most of any Uranian moon.
William Lassell discovered Ariel and Umbriel on the very same night in 1851.
How an old moon gets a young face
Ariel formed with the rest of the Uranian system over four billion years ago, yet much of its surface is far younger. Ancient orbital resonances with neighbouring moons likely flexed and heated its interior, letting slushy, viscous ice flood the floors of its rift valleys and bury old craters. A young surface never means a young world - it means the world found the energy to repave itself.
Physical characteristics
Diameter
1,158 km
Mass
1.350e+21 kg
Surface gravity
0.27 m/s²
Density
1.67 g/cm³
Tidally locked
Yes
Mean temperature
-200 °C
Geometric albedo
0.39
Atmosphere and composition
Atmosphere
None detected.
Composition
Roughly half water ice and half rock; carbon-dioxide ice has been detected on its surface.
Discovery
Discovered by
William Lassell
Year
1851
How
24-inch reflector at his private observatory
Missions
Voyager 2NASA · Flyby probe · 1977 · active
Launched 16 days before its twin, Voyager 2 is the only spacecraft ever to visit all four giant planets - Jupiter, Saturn, Uranus and Neptune. It entered interstellar space in 2018 and is still returning data.