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.