Editing Miranda (moon) (section)

== Composition and internal structure ==
[[File:ModestMiranda.jpg|thumb|Miranda compared to [[1 Ceres]] and the [[Moon]]]]
At 1.15&nbsp;g/cm<sup>3</sup>, Miranda is the least dense of Uranus's round satellites. That density suggests a composition of more than 60% water ice.{{sfn|Smith|1986}} Miranda's surface may be mostly water ice, though it is far rockier than its corresponding satellites in the Saturn system, indicating that heat from [[radioactive decay]] may have led to [[internal differentiation]], allowing [[silicate]] rock and [[organic compound]]s to settle in its interior.<ref name=Burgess/><ref name=blom>{{cite book|title=Uranus|editor=Jay T. Bergstralh |editor2=Ellis D. Miner |editor3=Mildred Shapley Matthews|year=1991|publisher=University of Arizona Press|chapter=Geology of the Uranian Satellites|author=S.K. Croft |author2=L. A. Brown|pages=309–319|isbn=978-0816512089}}</ref> Miranda is too small for any internal heat to have been retained over the age of the Solar System.<ref name=tanton/> Miranda is the least spherical of Uranus's satellites, with an equatorial diameter 3% wider than its polar diameter. Only water has been detected so far on Miranda's surface, though it has been speculated that [[methane]], [[ammonia]], [[carbon monoxide]] or nitrogen may also exist at 3% concentrations.<ref name=blom/><ref name=miner/> These bulk properties are similar to Saturn's moon [[Mimas (moon)|Mimas]], though Mimas is smaller, less dense, and more oblate.<ref name=miner/> A study published in 2024 suggests that Miranda might have had a liquid ocean of about 100 km thickness beneath the surface within the last 100-500 million years.<ref>{{cite journal |last1=Strom |first1=Caleb |last2=Nordheim |first2=Tom A. |last3=Patthoff |first3=D. Alex |last4=Fieber-Beyer |first4=Sherry K. |title=Constraining Ocean and Ice Shell Thickness on Miranda from Surface Geological Structures and Stress Modeling |journal=The Planetary Science Journal |date=1 October 2024 |volume=5 |issue=10 |pages=226 |doi=10.3847/PSJ/ad77d7|doi-access=free |bibcode=2024PSJ.....5..226S }}</ref> Some studies argue that Miranda may still possess a subsurface ocean.<ref>https://phys.org/news/2024-10-uranus-moon-miranda-ocean-beneath.html</ref><ref>https://www.newsweek.com/uranus-moon-miranda-subsurface-ocean-extraterrestrial-life-1977283</ref>

Precisely how a body as small as Miranda could have enough internal energy to produce the myriad geological features seen on its surface has not been established with certainty,<ref name=tanton>{{cite book|title=Uranus, Neptune, Pluto and the Outer Solar System|author=Lindy Elkins-Tanton|year=2006|isbn=978-0816051977|publisher=Facts On File|author-link=Lindy Elkins-Tanton|url-access=registration|url=https://archive.org/details/uranusneptuneplu00elki}}</ref> though the currently favoured hypothesis is that it was driven by [[tidal heating]] during a past time when it was in 3:1 orbital resonance with Umbriel.{{sfn|Tittemore|Wisdom|1990}} The resonance would have increased Miranda's [[orbital eccentricity]] to 0.1, and generated tidal friction due to the varying [[tidal force]]s from Uranus.{{sfn|Croft|Greenberg|1991}} As Miranda approached Uranus, tidal force increased; as it retreated, tidal force decreased, causing flexing that would have warmed Miranda's interior by 20 K, enough to trigger melting.{{sfn|Tittemore|Wisdom|1989}}{{sfn|Malhotra|Dermott|1990}}{{sfn|Croft|Greenberg|1991}} The period of tidal flexing could have lasted for up to 100 million years.{{sfn|Croft|Greenberg|1991}} Also, if [[clathrate]] existed within Miranda, as has been hypothesised for the satellites of Uranus, it may have acted as an insulator, since it has a lower conductivity than water, increasing Miranda's temperature still further.{{sfn|Croft|Greenberg|1991}} Miranda may have also once been in a 5:3 orbital 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.{{sfn|Tittemore|Wisdom|1990}}