The largest Uranian satellites are also icy, but are much darker and also denser than Saturn's satellites, presumably due to having dirtier surfaces and rockier interiors. Nonetheless, they probably have differentiated to the point that they have distinctly icy crusts and mantles and rocky cores. The ices, in addition to that of water, may be more exotic, including ammonia hydrate, methane-water mixtures, and others. These other chemicals, when they occur with water, could allow for thick, ice-lava flows, even at the extremely cold temperatures (-200 oC) in that part of the Solar System. The carbonaceous nature of these ice-mixtures would cause them to darken on exposure to solar radiation and cosmic rays. Darkening also probably occurs from accumulation of meteoritic material. All of the large Uranian satellites now seem to be geologically inactive, but most still show signs of past activity.Miranda perhaps contradicts the tenet that larger bodies are more active, as this diminutive satellite exhibits a bizarre surface. Ovoid terrain's, or coronae, which possess crude concentric color bands and exhibit concentric fault systems as well, may have been formed by an as-yet-to-be-understood process of outflow of material from the interior. Two of Miranda's coronae show indications of cryovolcanic flows associated with them. Another possible origin is that the coronae are simple upwellings due to thermal convection of the interior, possibly driven by tidal forces. A large canyon with a nearly 20-km vertical offset (Verona Rupes) suggests titanic forces at work. Such anomalously large features on such a small satellite also suggest an unusual origin, perhaps being caused by the total disruption of Miranda by an impact, leaving the body in a state of disequilibrium-the coronae and faults being the result of the re-establishment of equilibrium.