Umbriel and Ariel
Umbriel and Ariel are roughly three-fourths the size of Oberon and Titania. Umbriel is the darkest of the large moons, with huge craters peppering its surface. Umbriel has a paucity of what are known as bright ray craters, which are formed on an older, darker surface when bright, submerged ice is excavated and sprayed by meteoroid impacts.
In contrast, the surface of Ariel, the brightest of the Uranian moons, is relatively free of pockmarks due to volcanism that periodically erases the damage done by foreign projectiles. However, there are several extremely deep cuts on Ariel's surface.
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