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Uranus V

The ice giant Uranus has numerous moons, with nearly thirty being presently known, but only five of these are large enough to hold a spherical shape. Miranda is by far the smallest of these five (indeed, with a diameter of just 472km, it is probably close to the mass limit for forming a spherical moon). It is also the innermost of Uranus' major moons, although the space between Miranda and the planet is occupied by a swarm of tiny inner moons and fine rings.

By convention, Uranian moons are named for Shakespearean characters, and Miranda follows this pattern. In The Tempest, Miranda is the daughter of the sorceror Prospero (and Prospero also has a moon of Uranus named for him, though it is much smaller and more distant from the planet than Miranda).

Along with the other major moons, Miranda orbits Uranus near its equatorial plane, but in Uranus' case this has unusual consequences. Probably due to an immense ancient collision, Uranus' axis of rotation is tilted over at nearly 90° to the plane of the Solar System, and the orbits of its regular moons follow this tilted orientation. Thus Miranda and its fellow moons pursue orbits perpendicular to the plane of the rest of the Solar System - in other words, their orbits carry them back and forth across the Ecliptic plane. To an observer on Miranda, the Sun would not rise and set on opposite horizons, but rather it would appear to follow a tight looping path in one part of the sky.

Miranda has a rocky core, but its mantle and outer surface consist of a deep layer of water ice, probably represnting the majority of the moon's mass. The surface ice has been twisted and buckled to a remarkable degree, probably due to the effect of tidal heating in the past (though this is no longer considered to be a significant factor).

Among its surface features, Miranda is one of the few known bodies to possess coronae, ring-like geological forms thought to form as columns of material well up from below onto the surface. Several similar structures are known on the surface of Venus, for example, but Miranda also has three known examples. Following the Shakespearean tradition these are named Arden, Elsinore and Inverness, and it is thought that there may be more coronae on Miranda waiting to be discovered.


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