Editing Charon (moon) (section)

=== Surface ===
{{See also|Kubrick Mons}}
[[File:CharonFeatureMap Annotated.png|thumb|A map of Charon with [[International Astronomical Union|IAU]] names|center|upright=3]]
[[File:Pluto & Charon - Mountains Craters and Plains.jpg|thumb|Comparison between Pluto's [[Sputnik Planitia]] and Charon's informally named [[Vulcan Planitia]]]]
Unlike Pluto's surface, which is composed of [[nitrogen]] and [[methane]] ices, Charon's surface appears to be dominated by the less [[Volatile (astrogeology)|volatile]] water ice.

In 2007, observations by the [[Gemini Observatory]] detected patches of ammonia hydrates and water crystals on the surface of Charon that suggested the presence of active [[Geyser#Cryogeysers|cryogeysers]] and [[cryovolcano]]es. The fact that the ice was still in crystalline form suggested it may have been deposited recently, as it was expected that solar radiation would have degraded it to an [[Amorphous ice|amorphous]] state after roughly thirty thousand years.<ref name="ice"/><ref name="cook2007" /> However, following new data from the ''New Horizons'' flyby, no active cryovolcanoes or geysers were detected. Later research has also called into question the cryovolcanic origin for the crystalline water ice and ammonia features, with some researchers instead proposing that ammonia may be replenished passively from underground material.<ref name="holler2017"/>

Photometric mapping of Charon's surface shows a latitudinal trend in [[albedo]], with a bright equatorial band and darker poles. The north polar region is dominated by a very large dark area informally dubbed "[[Mordor Macula|Mordor]]" by the ''New Horizons'' team.<ref name="theweekmordor"/><ref name="NBC1"/><ref name="NYTmountains"/> The favored explanation for this feature is that it is formed by condensation of gases that escaped from [[Atmosphere of Pluto|Pluto's atmosphere]]. In winter, the temperature is −258&nbsp;°C, and these gases, which include nitrogen, carbon monoxide, and methane, condense into their solid forms; when these ices are subjected to solar radiation, they chemically react to form various reddish [[tholin]]s. Later, when the area is again heated by the Sun as Charon's seasons change, the temperature at the pole rises to −213&nbsp;°C, resulting in the volatiles sublimating and escaping Charon, leaving only the tholins behind. Over millions of years, the residual tholin builds up thick layers, obscuring the icy crust.<ref name="physorgmordor"/> In addition to Mordor, ''New Horizons'' found evidence of extensive past geology that suggests that Charon is probably differentiated;<ref name="NBC1" /> in particular, the southern hemisphere has fewer craters than the northern and is considerably less rugged, suggesting that a massive resurfacing event—perhaps prompted by the partial or complete freezing of an internal ocean—occurred at some point in the past and removed many of the earlier craters.<ref name="skyandtelescope2015"/>

Charon has a system of extensive [[graben]]s and scarps, such as [[List of geological features on Charon|Serenity Chasma]], which extend as an equatorial belt for at least {{Cvt|1000|km||abbr=|-1}}. Argo Chasma potentially reaches as deep as {{Cvt|9|km||abbr=|0}}, with cliffs that may rival [[Verona Rupes]] on [[Miranda (moon)|Miranda]] for the title of the tallest cliff in the Solar System.<ref name="nasa2017"/>