Despite its small size (only 470 kilometers across), Uranus' small icy satellite Miranda has had a surprisingly diverse and complex geologic history, concentrated in three dark oval- to square-shaped regions called coronae. This image shows portions of two coronae, Arden Corona at lower left and Inverness Corona at right. Coronae are 100-300 kilometers across and consist of a central zone of chaotic ridges surrounded by a zone of concentric ridges and fractures. Ridges appear to be extensional fault blocks in some areas and volcanic extrusions in other areas. The extruded ridges are up to 2 kilometers high and may be composed of ammonia-water lavas.
The concentric pattern of volcanism and tectonism within coronae suggests that they formed over plumes of material rising from the core of Miranda. These plumes spread out as they neared the surface, fracturing the crust and triggering local volcanism. The geologic complexity of Miranda is puzzling because it should have been cold and inactive since shortly after its formation. The heat required to melt large parts of the interior may have been provided by tidal interactions with neighboring satellites and Uranus itself. Similar tidal heating powers the volcanism on Jupiter's moon Io. (Voyager 2 images 26846.11, 26846.14, 26846.26.)