Changes

Miranda has the most striking landscape of any spheroidal celestial body other than the earth. Its largest surface features are extremely striking in their bizarre variety and stark relief, almost as if Miranda were an object that someone pieced together out of scrap metal.<ref name=planetsoc>"[http://www.planetary.org/explore/topics/uranus/miranda.html Uranus' Moon Miranda]." The Planetary Society. Accessed April 28, 2008.</ref> Twenty-kilometer canyons<ref name=nasa1/><ref name=Arnett/> give way to cratered regions<ref name=planetsoc/> and other regions nearly devoid of craters. The mixture of geologically "old" and "young" regions is quite puzzling.<ref name=nasa1/>

Miranda has the most striking landscape of any spheroidal celestial body other than the earth. Its largest surface features are extremely striking in their bizarre variety and stark relief, almost as if Miranda were an object that someone pieced together out of scrap metal.<ref name=planetsoc>"[http://www.planetary.org/explore/topics/uranus/miranda.html Uranus' Moon Miranda]." The Planetary Society. Accessed April 28, 2008.</ref> Twenty-kilometer canyons<ref name=nasa1/><ref name=Arnett/> give way to cratered regions<ref name=planetsoc/> and other regions nearly devoid of craters. The mixture of geologically "old" and "young" regions is quite puzzling.<ref name=nasa1/>

==Difficulties for uniformitarian theories==

==Difficulties for uniformitarian theories==

The current favored theory is that Miranda was once in a 1:3 orbital resonance with [[Umbriel]], and then escaped that resonance. While Miranda was resonating with Umbriel, its orbit gained in eccentricity and thus subjected it to [[tidal heating]]. To support that theory, astronomers point out that Miranda's orbit, inclined 4.22° from Uranus' equator, is more severely inclined than that of any other satellite in the Uranian system.<ref>Tittemore, William C., and Wisdom, Jack. "Tidal evolution of the Uranian satellites II. An explanation of the anomalously high orbital inclination of Miranda." ''Icarus'' 78(1):63-89, March 1989. Accessed April 28, 2008. <doi:10.1016/0019-1035(89)90070-5></ref><ref>Tittemore, William C., and Wisdom, Jack. "Tidal evolution of the Uranian satellites III. Evolution through the Miranda-Umbriel 3:1, Miranda-Ariel 5:3, and Ariel-Umbriel 2:1 mean-motion commensurabilities." ''Icarus'' 85(2):394-443, June 1990. Accessed April 28, 2003. <doi:10.1016/0019-1035(90)90125-S></ref><ref>Malhotra, Renu, and Dermott, Stanley F. "The role of secondary resonances in the orbital history of Miranda." ''Icarus'' 85(2):444-480, June 1990. <doi:10.1016/0019-1035(90)90126-T></ref> Some believe that this tidal heating caused an upwelling of subsurface ice that produced some of the most pronounced surface features.<ref>Pappalardo, R. T., S. J. Reynolds, and R. Greeley (1997), [http://www.agu.org/pubs/crossref/1997/97JE00802.shtml Extensional tilt blocks on Miranda: Evidence for an upwelling origin of Arden Corona], ''J. Geophys. Res''., 102(E6), 13,369–13,379.</ref>

The current favored theory is that Miranda was once in a 1:3 orbital resonance with [[Umbriel]], and then escaped that resonance. While Miranda was resonating with Umbriel, its orbit gained in eccentricity and thus subjected it to [[tidal heating]]. To support that theory, astronomers point out that Miranda's orbit, inclined 4.22° from Uranus' equator, is more severely inclined than that of any other satellite in the Uranian system.<ref>Tittemore, William C., and Wisdom, Jack. "Tidal evolution of the Uranian satellites II. An explanation of the anomalously high orbital inclination of Miranda." ''Icarus'' 78(1):63-89, March 1989. Accessed April 28, 2008. <doi:10.1016/0019-1035(89)90070-5></ref><ref>Tittemore, William C., and Wisdom, Jack. "Tidal evolution of the Uranian satellites III. Evolution through the Miranda-Umbriel 3:1, Miranda-Ariel 5:3, and Ariel-Umbriel 2:1 mean-motion commensurabilities." ''Icarus'' 85(2):394-443, June 1990. Accessed April 28, 2003. <doi:10.1016/0019-1035(90)90125-S></ref><ref>Malhotra, Renu, and Dermott, Stanley F. "The role of secondary resonances in the orbital history of Miranda." ''Icarus'' 85(2):444-480, June 1990. <doi:10.1016/0019-1035(90)90126-T></ref> Some believe that this tidal heating caused an upwelling of subsurface ice that produced some of the most pronounced surface features.<ref>Pappalardo, R. T., S. J. Reynolds, and R. Greeley (1997), [http://www.agu.org/pubs/crossref/1997/97JE00802.shtml Extensional tilt blocks on Miranda: Evidence for an upwelling origin of Arden Corona], ''J. Geophys. Res''., 102(E6), 13,369–13,379.</ref>

But this begs the question of how orbital resonances form, or how a satellite, once in such a resonance, would escape it. More to the point, however, is that the orbit of Miranda is not the most strikingly eccentric orbit in the Uranian system. Even among the major moons, that distinction belongs to Umbriel, not Miranda.

Image:MirandaSouth.jpg|South pole region showing some of Miranda's most striking features

Image:MirandaFault.jpg|High-resolution image of a fault line

== References ==

== References ==