Object Analysis

Ariel is the fourth-largest of the 28 known moons of Uranus. It was discovered in 1851 by William Lassell. Like most of the Uranian moons, Ariel is composed of roughly equal parts ice and rock. It is the brightest of the large Uranian moons and shows evidence of significant geological activity in its past.

The surface of Ariel is crisscrossed by an extensive network of "grabens"—deep, steep-walled valleys formed by the stretching of the moon's crust. Many of these valleys appear to have been partially filled by flows of "cryolava" (liquid water or ammonia ice), suggesting that the moon remained geologically active much longer than its neighbors.

Ariel has relatively few large impact craters compared to moons like Umbriel, indicating that its surface is younger and has been "wiped clean" by geological processes. The heat required for this activity likely came from tidal friction caused by past orbital resonances with other moons in the Uranian system.