Changes

The geological activity required to produce Miranda's striking mix of surface features defies explanation.<ref name=Chaikin>Chaikin, Andrew. "[http://www.space.com/scienceastronomy/solarsystem/miranda_creation_011016-1.html Birth of Uranus' Provocative Moon Still Puzzles Scientists]." <http://www.space.com/> October 16, 2001. Accessed April 28, 2008.</ref>

The geological activity required to produce Miranda's striking mix of surface features defies explanation.<ref name=Chaikin>Chaikin, Andrew. "[http://www.space.com/scienceastronomy/solarsystem/miranda_creation_011016-1.html Birth of Uranus' Provocative Moon Still Puzzles Scientists]." <http://www.space.com/> October 16, 2001. Accessed April 28, 2008.</ref>

Shortly after the Voyager 2 flyby, [[Astronomy|astronomers]] proposed that Miranda was shattered five times by collisions and then reassembled by mutual gravitational attraction.<ref name=Chaikin/><ref name=Arnett/><ref name=planetsoc/><ref name=nasa1/> But such a small moon would not be likely to survive even one collision, much less five. This theory is now out of favor.

Shortly after the Voyager 2 flyby, [[Astronomy|astronomers]] proposed that Miranda was shattered five times by collisions and then reassembled by mutual gravitational attraction.<ref name=nasa1/><ref name=Arnett/><ref name=planetsoc/><ref name=Chaikin/> But such a small moon would not be likely to survive even one collision, much less five. This theory is now out of favor.

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>