Editing Triton (moon) (section)

== Physical characteristics ==
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 |caption1=Triton dominates the Neptunian moon system, with over 99.5% of its total mass. This imbalance may reflect the elimination of many of Neptune's original satellites following Triton's capture.<ref name="JPL-SSD-Neptune"/><ref name="Jacobson2009-AJ"/>
 |caption2=Triton (''lower left'') compared to the Moon (''upper left'') and Earth (''right''), to scale
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Triton is the seventh-largest moon and [[List of Solar System objects by size|sixteenth-largest object]] in the Solar System and is modestly larger than the [[dwarf planet]]s [[Pluto]] and [[Eris (dwarf planet)|Eris]]. It is also the largest retrograde moon in the Solar System. It accounts for more than 99.5% of all the mass known to orbit Neptune, including the planet's rings and fifteen other known moons,<ref name="nMassTriton" group="lower-alpha"/> and is also more massive than all known moons in the Solar System smaller than itself combined.<ref name="nMassOthers" group="lower-alpha"/> Also, with a diameter 5.5% that of Neptune, it is the largest moon of a gas giant relative to its planet in terms of diameter, although Titan is bigger relative to Saturn in terms of mass (the ratio of Triton's mass to that of Neptune is approximately 1:4788). It has a radius, density (2.061 g/cm<sup>3</sup>), temperature, and chemical composition similar to that of [[Pluto]].<ref name="voyager"/>

Triton's surface is covered with a transparent layer of [[annealing (metallurgy)|annealed]] [[solid nitrogen|frozen nitrogen]]. Only 40% of Triton's surface has been observed and studied, but it may be entirely covered in such a thin sheet of nitrogen ice. Triton's surface consists of 55% nitrogen ice with other ices mixed in. [[Water]] ice comprises 15–35% and frozen [[carbon dioxide]] ([[dry ice]]) the remaining 10–20%. Trace ices include 0.1% [[methane]] and 0.05% [[carbon monoxide]].<ref name="EncycSolSys-Triton"/>{{rp|868}} There could also be [[ammonia]] ice on the surface, as there are indications of ammonia [[dihydrate]] in the [[lithosphere]].<ref name="ammonia"/> Triton's mean density implies that it probably consists of about 30–45% [[ice|water ice]] (including relatively small amounts of volatile ices), with the remainder being rocky material.<ref name="EncycSolSys-Triton"/> Triton's surface area is 23&nbsp;million&nbsp;km<sup>2</sup>, which is 4.5% of [[Earth]], or 15.5% of Earth's land area. Triton has an unusually high [[albedo]], reflecting 60–95% of the sunlight that reaches it, and it has changed only slightly since the first observations. By comparison, the Moon reflects only 11%.<ref name="Medkeff2002-LunarAlbedo"/> This high albedo causes Triton to reflect a lot of whatever little sunlight there is instead of absorbing it,<ref>{{cite web | url=https://phys.libretexts.org/Bookshelves/Astronomy__Cosmology/Astronomy_1e_(OpenStax)/12%3A_Rings_Moons_and_Pluto/12.03%3A_Titan_and_Triton | title=12.3: Titan and Triton | date=October 7, 2016 }}</ref><ref>{{cite web | url=https://sos.noaa.gov/catalog/datasets/triton-neptunes-moon/ | title=Triton: Neptune's Moon | date=January 2010 }}</ref> causing it to have the coldest recorded temperature in the Solar System at {{cvt|38|K|C|0}}.<ref>{{cite web | url=https://science.nasa.gov/neptune/moons/triton/#hds-sidebar-nav-1 | title=Triton – NASA Science | access-date=January 7, 2024 | archive-date=January 7, 2024 | archive-url=https://web.archive.org/web/20240107182347/https://science.nasa.gov/neptune/moons/triton/#hds-sidebar-nav-1 | url-status=dead }}</ref><ref>{{cite journal |author=Nelson, R.M. |display-authors=4 |author2=Smythe, W.D. |author3=Wallis, B.D. |author4=Horn, L.J. |author5=Lane, A.L. |author6=Mayo, M.J. |title=Temperature and Thermal Emissivity of the Surface of Neptune's Satellite Triton |journal=Science |date=1990 |volume=250 |issue=4979 |pages=429–431 |doi=10.1126/science.250.4979.429 |pmid=17793020 |bibcode=1990Sci...250..429N|s2cid=20022185 }}</ref> Triton's reddish color is thought to be the result of methane ice, which is converted to [[tholin]]s under exposure to [[ultraviolet]] radiation.<ref name="EncycSolSys-Triton"/><ref name="Grundy"/>

Because Triton's surface indicates a long history of melting, models of its interior posit that Triton is differentiated, like [[Earth]], into a solid [[core (geology)|core]], a [[mantle (geology)|mantle]] and a [[crust (geology)|crust]]. [[Water]], the most abundant [[Volatile (astrogeology)|volatile]] in the Solar System, comprises Triton's mantle, enveloping a core of rock and metal. There is enough rock in Triton's interior for [[radioactive decay]] to maintain a liquid [[subsurface ocean]] to this day, similar to what is thought to exist beneath the surface of [[Europa (moon)|Europa]] and several other icy outer Solar System worlds.<ref name="EncycSolSys-Triton"/><ref name="Hussman2006"/><ref name='Sci Am 2017'>{{cite web |url=https://www.scientificamerican.com/article/overlooked-ocean-worlds-fill-the-outer-solar-system/ |title=Overlooked Ocean Worlds Fill the Outer Solar System |first=John |last=Wenz |work=Scientific American |date=October 4, 2017}}</ref><ref name="Nimmo2015">{{cite journal |last1=Nimmo |first1=Francis |title=Powering Triton's recent geological activity by obliquity tides: Implications for Pluto geology |journal=Icarus |date=January 15, 2015 |volume=246 |pages=2–10 |doi= 10.1016/j.icarus.2014.01.044 |bibcode=2015Icar..246....2N |s2cid=40342189 |url=https://escholarship.org/content/qt99s8t6zm/qt99s8t6zm.pdf?t=nnm476 }}</ref> This is not thought to be adequate to power convection in Triton's icy crust. However, the strong [[obliquity]] [[Tidal Heating|tides]] are believed to generate enough additional heat to accomplish this and produce the observed signs of recent surface geological activity.<ref name="Nimmo2015"/> The black material ejected is suspected to contain [[organic compound]]s,<ref name="Sci Am 2017"/> and if liquid water is present on Triton, it has been speculated that this could make it [[Planetary habitability|habitable]] for some form of life.<ref name='Sci Am 2017'/><ref name="Irwin2001-Plausibility"/><ref name="space.com">{{cite web | url=http://www.space.com/17470-neptune-moon-triton-subsurface-ocean.html | title=Does Neptune's moon Triton have a subsurface ocean? | work=Space.com | date=September 6, 2012 | access-date=September 18, 2015 | author=Doyle, Amanda}}</ref>