Orbit and geology of Uranus's moon Miranda, illustration. One of the theories explaining the surface features of Miranda, one of the moons of the planet Uranus, is that its orbit varied in the past. It may have been locked into an orbital resonance with another moon Umbriel. This resonance is shown at upper left, with Umbriel the outer of the two moons. The orbit (red ellipse) of Miranda is shown changing to a more eccentric one (more elliptical). This increased the tidal effects as shown at upper right (yellow arrows). This heated the interior of Miranda (lower left), leading to tectonic plate-like movements to form the rifts and canyons shown at lower right (yellow arrows showing surface movements).