Of Uranus's five major moons, Ariel is the second-closest to Uranus, orbiting about 191,020 km away once every 2.5 days or so, and the fourth in size, at around 1,157.8 km in diameter.  It probably comprises more or less equal parts ice and rock with a rocky core with a mantle of ice around it.  It is heavily cratered with many canyons and ridges. 

Like Uranus itself, Ariel orbits on its side so the north and south poles alternately point towards the sun.  Each receives continuous sunlight for half the year, where the Uranian year is more than 84 Earth years, resulting in extreme changes in climate! 

Uranus' Moon Ariel