Miranda (moon) - Physical Characteristics

Physical Characteristics

The surface area of Miranda is approximately equal to the land area of Texas. Miranda's surface may be mostly water ice, with the low-density body also probably containing silicate rock and organic compounds in its interior.

Miranda's surface has patchwork regions of broken terrain indicating intense geological activity in the moon's past, and is criss-crossed by huge canyons. Large 'racetrack'-like grooved structures, called coronae, may have formed via extensional processes at the tops of diapirs, or upwellings of warm ice. The ridges probably represent extensional tilt blocks. The canyons probably represent graben formed by extensional faulting. Other features may be due to cryovolcanic eruptions of icy magma. The diapirs may have changed the density distribution within the moon, which could have caused Miranda to reorient itself, similar to a process believed to have occurred at Saturn's geologically active moon Enceladus.

Miranda's past geological activity is believed to have been driven by tidal heating at a time when its orbit was more eccentric than currently. Early in its history, Miranda was apparently captured into a 3:1 orbital resonance with Umbriel, from which it subsequently escaped. The resonance would have increased orbital eccentricity; resulting tidal friction due to time-varying tidal forces from Uranus would have caused warming of the moon's interior. In the Uranian system, due to the planet's lesser degree of oblateness, and the larger relative size of its satellites, escape from a mean motion resonance is much easier than for satellites of Jupiter or Saturn. Miranda's orbital inclination (4.34°) is unusually high for a body so close to the planet. Miranda probably escaped from its resonance with Umbriel via a secondary resonance, and the mechanism of this escape is believed to explain why its orbital inclination is more than 10 times those of the other large Uranian moons (see moons of Uranus).

Miranda may have also once been in a 5:3 resonance with Ariel, which would have also contributed to its internal heating. However, the maximum heating attributable to the resonance with Umbriel was likely about three times greater.

An earlier theory, proposed shortly after the Voyager 2 flyby, was that a previous incarnation of Miranda was shattered by a massive impact, with the fragments reassembling and denser ones subsequently sinking to produce the current strange pattern.

Scientists recognize the following geological features on Miranda:

• Craters
• Coronae (large ovoid features)
• Regiones (geological regions)
• Rupes (scarps)
• Sulci (parallel grooves)