{{Short description|Natural satellite with a surface mainly composed of ice}} [[File:PIA07763 Rhea full globe5.jpg|thumb|Rhea, the second-largest moon of Saturn and the ninth-largest in the Solar System, is around 3/4 ice by mass.<ref name="Anderson2007">{{cite journal |last1= Anderson|first1=J. D.|last2= Schubert|first2= G.|title= Saturn's satellite Rhea is a homogeneous mix of rock and ice|journal= Geophysical Research Letters |volume= 34|issue= 2|pages=L02202|year= 2007|doi= 10.1029/2006GL028100|bibcode= 2007GeoRL..34.2202A|doi-access= free}}</ref>]]
'''Icy moons''' are a class of natural satellites with surfaces composed mostly of ice. An icy moon may harbor an ocean underneath the surface, and possibly include a rocky core of silicate or metallic rocks.<ref>{{cite journal | title=The Physical Oceanography of Ice-Covered Moons | display-authors=1 | last1=Soderlund | first1=Krista M. | last2=Rovira-Navarro | first2=Marc | last3=Le Bars | first3=Michael | last4=Schmidt | first4=Britney E. | last5=Gerkema | first5=Theo | journal=Annual Review of Marine Science | volume=16 | pages=25–53 | date=January 2023 | doi=10.1146/annurev-marine-040323-101355 | pmid=37669566 | bibcode=2023ARMS...16...25S | doi-access=free }}</ref> It is thought that they may be composed of ice II or other polymorph of water ice.<ref name="Ice_II_structure">{{cite web |url=http://www.lsbu.ac.uk/water/ice_ii.html |title=Ice-two structure |accessdate=2008-01-02 |author=Chaplin, Martin |date=2007-10-26 |work=Water Structure and Science |archive-date=2012-04-27 |archive-url=https://web.archive.org/web/20120427030534/http://www.lsbu.ac.uk/water/ice_ii.html |url-status=dead }}</ref> The prime example of this class of object is Europa.
Icy moons warmed by tides may be the most common type of celestial body in the galaxy to have liquid water,<ref>{{Cite web |date=2024-10-12 |title=Can Life Exist on an Icy Moon? NASA's Europa Clipper Aims to Find Out – NASA |url=https://www.nasa.gov/missions/europa-clipper/can-life-exist-on-an-icy-moon-nasas-europa-clipper-aims-to-find-out/ |access-date=2024-11-18 |language=en-US}}</ref> and thus the most likely type of object to possibly have water-based life.
Some icy moons exhibit cryovolcanism, as well as geysers. The best studied example is Saturn's Enceladus.
==Orbits== Most known large icy moons belong to giant planets, whose orbits lie beyond the Solar System's frost line; the remainder (such as Charon and Dysnomia) formed around dwarf planets such as Pluto and {{dp|Eris}}, typically in large impacts not unlike the impact thought to have formed Earth's moon. In the case of icy gas giant satellites, an additional requirement is that a moon did not form in the inner region of a proto-satellite disk, which is too warm for ices to condense.
Europa is thought to contain 8% ice and water by mass with the remainder rock.<ref name="arxiv0812">{{cite book |arxiv= 0812.4995 |author1= Canup, Robin M. |author1-link=Robin Canup |author2= Ward, William R. |authorlink2=William Ward (astronomer) |title= Origin of Europa and the Galilean Satellites |year=2008 |bibcode= 2009euro.book...59C |page= (page needed) }}</ref> Jupiter's outer two Galilean moons Ganymede and Callisto contain more ice since they formed further from the hot proto-Jupiter.
Saturn's moon Titan looks and behaves more like Earth than any other body in the Solar System.<ref name="IAU0915">{{cite web |date=2009-08-06 |title=Surface features on Titan form like Earth's, but with a frigid twist |publisher=IAU |author1=Rosaly Lopes |author1-link=Rosaly Lopes |author2=Robert M. Nelson |url=http://www.iau.org/public_press/news/detail/iau0915/ |accessdate=2009-12-21 |archive-date=2009-09-26 |archive-url=https://web.archive.org/web/20090926080025/http://www.iau.org/public_press/news/detail/iau0915/ |url-status=dead }}</ref> Titan is known to have stable pools of liquid methane on the surface.<ref name="IAU0915"/>
==Images== <gallery> Image:PIA01130 Interior of Europa.jpg|Europa is thought to have a subsurface ocean. Image:Ganymede-moon.jpg|False-color image of Ganymede Image:Callisto VGR2 C2060635 OGB.png|Callisto showing frost deposits Image:Mimas moon.jpg|Mimas has a density of 1.1 g/cm<sup>3</sup>. Image:Successful Flight Through Enceladus Plume.jpg|Active plumes on Enceladus Image:Titan multi spectral overlay.jpg|False-color image of Titan showing surface and atmospheric details Miranda mosaic in color - Voyager 2.png|Miranda has a scarred surface. File:PIA00040 Umbrielx2.47.jpg|A potential frost deposit on Umbriel's pole Image:Tritoncloud.jpg|A cloud over the limb of Triton </gallery>
==See also== *Ocean planet *Ice planet *Tectonics on icy moons
== References == {{reflist}}
{{Solar System moons (compact)}}
{{DEFAULTSORT:Icy Moon}} Category:Moons Moon