Miranda and Ariel are the innermost of Uranus's five largest moons, about one seventh and one third of the size of Earth's moon, respectively. Both appear to be roughly half ice and half rock. Titania and Oberon, Uranus's two largest moons, are the farthest large moons from Uranus and also seem to be composed of about half ice and half rock. None of the five largest moons of Uranus have any detectable atmosphere or magnetic field. This contrasts sharply with the moons of Jupiter, the compositional and atmospheric characteristics of which differ based on the moon's distance from the planet.
Despite their compositional similarities, the geographies of the moons of Uranus differ greatly. Miranda, the smallest of the five major moons, has huge canyons, some of which are 12 miles deep, a characteristic that is especially notable given that the moon itself has a diameter of only 290 miles. Miranda's entire surface is marked by massive faults, steep cliffs, smooth plains, and curiously shaped rifts; these features indicate a significant amount of recent geological activity. Ariel, on the other hand, has a few larger craters on the surface, but most are small. Many of Ariel's craters seem to be submerged to some degree. This indicates that the surface is relatively young, having been reshaped by geological movement. On Titania, a number of rift valleys, similar to those on Ariel but less extensive, crisscross the moon's surface. Titania's surface also reveals several faults; these indicate that the most recent geological activity on the moon was a very long time ago. Similarly, Oberon, the outermost of the five major moons, hasn't changed much recently. Its impact craters are more common and much bigger than the craters on Ariel and Titania, but its faults are limited to the southern hemisphere and are old enough to indicate a lack of geological activity anytime in recent history.