Oberon was discovered by Herschel in 1787.

Oberon and Umbriel appear quite similar though Oberon is 35% larger. All of Uranus' large moons are a mixture of about 40-50% water ice with the rest rock.

Oberon's heavily cratered surface has probably been stable since its formation. It has far more and larger craters than do Ariel and Titania. 
   Some of the crater floors are dark, perhaps covered with darker material 
(dirty water?) that upwelled into the crater.

   Large faults are also seen across the entire southern hemisphere of Oberon. This indicates some geologic activity early in Oberon's history.