Ariel is similar in size and mass to Umbriel, but whereas Umbriel is the darkest of Uranus' five largest
satellites, Ariel is the brightest, with a 0.40 average albedo. Ariel's surface seems to have evolved more like Titania's surface than that of Umbriel; it shows global-scale faulting (canyons, scarps, and lineaments) and resurfacing by cryovolcanism, but on a more extensive scale than occurred on Titania. Ariel's most heavily cratered plains show less cratering than the most cratered units on Titania and Oberon. Evidence has been found for the extrusion of ice into Ariel's surface, filling part of a valley and partially burying an impact crater.