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| Miranda (moon) | |
|---|---|
| Name | Miranda |
| Discoverer | Gordon Cooper? |
| Discovered | 1948 |
| Named after | Miranda (character) |
| Mean radius | 235.8 km |
| Mass | 6.59×10^19 kg |
| Orbital period | 1.413 days |
| Semimajor axis | 129,900 km |
| Eccentricity | 0.0013 |
| Inclination | 4.338° (to Uranus's equator) |
| Satellites | none |
Miranda (moon) is a small, irregularly shaped natural satellite of Uranus notable for extreme surface heterogeneity, including giant canyons, terraced formations, and the distinctive coronae. Discovered in the mid-20th century and imaged in detail by Voyager 2, Miranda presents a mosaic of ancient cratered terrains and relatively young, tectonically reworked regions that have challenged models of satellite geophysics and planetary science.
Miranda was discovered during photographic surveys of Uranus undertaken by astronomers at Yerkes Observatory and confirmed by observations associated with the U.S. Naval Observatory and the Royal Greenwich Observatory. The name Miranda was proposed using characters from William Shakespeare's play The Tempest in keeping with the naming convention for Uranian satellites established by John Herschel and adopted by the International Astronomical Union. Miranda's naming parallels other Uranian moons such as Titania, Oberon, Ariel, and Umbriel.
Miranda orbits Uranus at a mean distance of approximately 129,900 kilometers with a sidereal period of about 1.413 days, lying well within Uranus's gravitational influence and interior to the orbit of Ariel. Its orbit exhibits low eccentricity and modest inclination relative to Uranus's equator, resulting from long-term interactions with Uranus's oblateness and perturbations by neighboring satellites such as Umbriel and Titania. Miranda is in no known mean-motion resonance today, though past resonant crossings with Umbriel and Ariel have been proposed to explain its internal heating and orbital evolution modeled alongside theories developed in celestial mechanics and studies by researchers at institutions like Caltech and NASA.
Miranda has a mean radius of about 235.8 km and a mass near 6.59×10^19 kg, giving it a low mean density (~1.2–1.3 g/cm^3) consistent with a mixture of water ice and rocky material inferred from gravimetry and radiometric analyses used by teams at Jet Propulsion Laboratory and Brown University. Miranda's surface gravity is only a few percent of Earth's, comparable to other small icy satellites like Mimas and Enceladus, and its escape velocity is correspondingly low. Miranda's low albedo variations, as measured by instruments on Voyager 2 and later ground-based facilities such as Palomar Observatory and Keck Observatory, reflect both bright water-ice and dark carbonaceous components seen on bodies like Dione and Rhea.
Miranda's surface is renowned for unique features including large coronae—Elis, Arden, and Inverness—characterized by concentric ridges, fault scarps, and deep canyons comparable in scale to features on Ganymede and Callisto. Terraced regions and fault-bounded blocks, reminiscent of those on Iapetus and Europa, suggest extensive tectonic disruption. Crater counts indicate regions of vastly different ages: heavily cratered terrain similar to Lunar highlands contrasts with geologically young plains and resurfaced areas analogous to processes inferred on Triton and Io. Surface spectroscopic mapping by Voyager 2 revealed water-ice absorption bands and possible organics similar to those detected on Charon and Phoebe.
Models for Miranda's interior, informed by its bulk density and moment-of-inertia estimates developed by groups at Cornell University and University College London, favor a differentiated or partially differentiated body with an icy mantle and a rock-rich core, consistent with compositions inferred for mid-sized satellites such as Ganymede (in part) and Callisto (partial differentiation). Thermal evolution scenarios incorporate radiogenic heating from isotopes like uranium-238 and tidal dissipation during putative past resonances with Umbriel or Ariel, paralleling heating mechanisms considered for Enceladus and Io. Laboratory measurements at institutions including MIT and University of Arizona on ice rheology inform models of Miranda's lithospheric strength and convective potential.
Miranda likely formed in the circumplanetary disk surrounding Uranus during the later stages of planetary accretion, similar to formation pathways proposed for other regular satellites such as Titania and Oberon. Its subsequent evolution reflects a combination of radiogenic heating, orbital migration, and episodic tidal heating possibly driven by resonant interactions with Umbriel and Ariel, as explored in dynamical studies at Princeton University and Stanford University. These processes could produce the localized upheaval and corona-forming events analogous to plume-driven resurfacing proposed for Enceladus and rift-driven resurfacing proposed for Europa.
Miranda's detailed imaging and spectroscopic datasets derive primarily from the Voyager 2 flyby on January 24, 1986, supplemented by Earth-based observations from facilities including Hubble Space Telescope, Keck Observatory, Very Large Telescope, and radio science experiments by Arecibo Observatory. Proposals for future missions, championed by teams at NASA centers and academic consortia such as the Planetary Society, include orbiters or Uranus flagship missions aimed at returning high-resolution mapping, gravity, and compositional measurements comparable to those obtained for Jupiter and Saturn systems by missions like Galileo and Cassini–Huygens.
Category:Moons of Uranus