Ariel was discovered by Lassel in 1851.

Ariel and Titania appear quite similar though Titania is 35% larger. All of Uranus' large moons are a mixture of about 40-50% water ice with the rest rock, a somewhat larger fraction of rock than Saturn's large moons such as Rhea.

Ariel's surface is a mixture of cratered terrain and systems of interconnected valleys hundreds of kilometers long  and more than 10 km deep. This is similar to, but much larger and more extensive than the situation on Titania. Some of the craters appear to be half-submerged. Ariel's surface is clearly relatively young. Some ridges in the middle of the valleys are interpreted as upwellings of ice.

   Ariel may have been hot inside long ago, but it's cold now. Perhaps the valleys are cracks which formed when Ariel froze.