Ariel is one of the major moons of Uranus and is considered the brightest and most geologically active-looking of the planet’s large satellites. Discovered in 1851 by William Lassell, Ariel is about 1,160 kilometers in diameter and is composed of a mixture of ice and rock, similar to Uranus’s other large moons. Its surface is marked by a striking combination of smooth plains, long canyons, fault scarps, and bright fractures that suggest relatively recent geological resurfacing compared to its neighbors. Many of Ariel’s canyons appear to have been shaped by flowing icy material or cryovolcanism—volcanic activity involving water or other frozen substances instead of molten rock. Its surface is brighter than most Uranian moons, reflecting more sunlight and giving scientists clues that fresh ice has been exposed or deposited within the last few hundred million years. Ariel orbits Uranus at about 191,000 kilometers and is tidally locked, keeping the same side facing the planet at all times. Like the other Uranian moons, it was photographed only once by Voyager 2 in 1986, meaning much of its far side remains unmapped and mysterious. The moon is named after the airy spirit Ariel from Shakespeare’s The Tempest, fitting its bright, clean appearance among the darker moons of Uranus.