Editing Neptune (section)

=== Mass and composition ===
Neptune's mass is between that of the [[Earth]] and the largest gas giants.<ref>At 102.413{{e|24}}[[kilogram|kg]],{{Cite web|title=Neptune Fact Sheet|url=https://nssdc.gsfc.nasa.gov/planetary/factsheet/neptunefact.html|access-date=June 14, 2021|website=nssdc.gsfc.nasa.gov|archive-date=January 3, 2023|archive-url=https://web.archive.org/web/20230103004627/https://nssdc.gsfc.nasa.gov/planetary/factsheet/neptunefact.html|url-status=dead}}</ref> Neptune is the fourth largest planet in the [[Solar System]] and the third most massive.<ref name=":13" /> Neptune is 17 times the mass of Earth, but just {{frac|1|18}} the mass of [[Jupiter]].<ref>Bradford A. Smith, «Neptune », 'World Book Online Reference Center', 2004, <abbr>p.</abbr> 5</ref> Neptune is a little bit more [[mass]]ive than [[Uranus]], though Neptune is denser and smaller in size than Uranus.<ref name=":13" /> Neptune and Uranus are often considered a part of "ice giants" (a sub-class of gas giants).<ref name=":13" /><ref name="doi.org">{{Cite journal|last1=Helled|first1=Ravit|last2=Nettelmann|first2=Nadine|last3=Guillot|first3=Tristan|date=March 25, 2020|title=Uranus and Neptune: Origin, Evolution and Internal Structure|url=https://doi.org/10.1007/s11214-020-00660-3|journal=Space Science Reviews|language=en|volume=216|issue=3|pages=38|doi=10.1007/s11214-020-00660-3|arxiv=1909.04891|bibcode=2020SSRv..216...38H|s2cid=202558606|issn=1572-9672}}</ref> They are smaller in size than Jupiter and [[Saturn]], and have different compositions. To search [[extrasolar planets]], Neptune has been used as a reference to compare the size and structure of other discovered planets. Some discovered planets that have similar masses like Neptune are often called "Neptunes".<ref>{{cite news|date=May 21, 2006|title=Trio of Neptunes|work=Astrobiology Magazine|url=https://www.eso.org/public/news/eso0618/|access-date=June 9, 2021}}</ref>

The atmosphere of Neptune is made up mostly of [[hydrogen]], with a smaller amount of [[helium]]. A tiny amount of [[methane]] was also detected in the atmosphere. The methane gives Neptune its blue color.<ref>{{Cite web|title=All About Neptune {{!}} NASA Space Place – NASA Science for Kids|url=https://spaceplace.nasa.gov/all-about-neptune/en/|access-date=June 12, 2021|website=spaceplace.nasa.gov}}</ref><ref name="Neptune">{{cite web|title=Neptune|url=http://solarsystem.nasa.gov/planets/profile.cfm?Object=Neptune|url-status=dead|archive-url=https://web.archive.org/web/20061213204351/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Neptune|archive-date=December 13, 2006|publisher=NASA|accessdate=November 11, 2010}}</ref> The color of Neptune is similar, but slightly darker, than the color of Uranus.<ref name="Neptune"/>

Because of Neptune's far distance from the [[Sun]], it gets very little heat. The average surface temperature on Neptune is about −201°[[Celsius|C]] (−331 °[[Fahrenheit|F]]; 72 [[Kelvin|K]]).<ref>{{Cite web|title=Solar System Temperatures|url=https://solarsystem.nasa.gov/resources/681/solar-system-temperatures|access-date=June 12, 2021|website=NASA Solar System Exploration}}</ref> Therefore, at its surface Neptune is the coldest planet in the Solar System. 

But in the depths of the planet, the temperature rises. The source of this heating is unclear.<ref>Broadfoot A.L.; Atreya S.K.; Bertaux J.L.; et al. 1999. Ultraviolet Spectrometer Observations of Neptune and Triton. ''Science''. '''246''' (4936): 1459–66. Bibcode:1989Sci...246.1459B. doi:10.1126/science.246.4936.1459. PMID 17756000. S2CID 21809358. Archived (PDF) from the original on May 28, 2008. Retrieved March 12, 2008.</ref><ref>Herbert, Floyd; Sandel, Bill R. August/September 1999. Ultraviolet observations of Uranus and Neptune. ''Planetary and Space Science'' '''47''' (8–9): 1, 119–139. Bibcode:1999P&SS...47.1119H. doi:10.1016/S0032-0633(98)00142-1</ref><ref>{{Cite book|url=https://books.google.com/books?id=bJoYlBWbCAYC&dq=the+source+of+heating+on+neptune+is+unknown&pg=PA75|title=Uranus, Neptune, Pluto, and the Outer Solar System|last=Elkins-Tanton|first=Linda T.|date=2006|publisher=Infobase Publishing|isbn=978-1-4381-0729-5|pages=75|language=en}}</ref> Neptune is the farthest planet from the Sun,<ref name=":13">{{Cite web|title=In Depth {{!}} Neptune|url=https://solarsystem.nasa.gov/planets/neptune/in-depth|access-date=June 14, 2021|website=NASA Solar System Exploration |date=10 November 2017 }}</ref> yet its internal energy is strong enough to create the fastest winds seen in the Solar System, at {{Convert|1,300|mph|km/h}}.<ref name="Suomi1991">{{cite journal|last1=Suomi|first1=V. E.|last2=Limaye|first2=S. S.|last3=Johnson|first3=D. R.|year=1991|title=High winds of Neptune - A possible mechanism|url=http://adsabs.harvard.edu/abs/1991Sci...251..929S|journal=Science|volume=251|issue=4996|pages=929–932|bibcode=1991Sci...251..929S|doi=10.1126/science.251.4996.929|pmid=17847386|s2cid=46419483}}</ref><ref name=":5">{{Cite web|last=Cain|first=Fraser|date=December 9, 2008|title=What is the Weather Like on Neptune?|url=https://www.universetoday.com/22067/weather-on-neptune/|access-date=June 12, 2021|website=Universe Today|language=en-US}}</ref> Several possible explanations have been suggested. Firstly, [[radiogenic]] heating from the planet's core. Among the explanations is the continued radiation into space of leftover heat made by [[Accretion theory|infalling matter]] during the planet's birth. Another explanation is [[gravity wave]]s breaking above the [[tropopause]]. It has also been suggested that the [[friction]] and [[ram pressure]] of the diamond [[hail]] heats up the planet.<ref>McHugh J.P. [http://www.aas.org/publications/baas/v31n4/dps99/572.htm Computation of gravity waves near the tropopause] {{Webarchive|url=https://web.archive.org/web/20071027135535/http://www.aas.org/publications/baas/v31n4/dps99/572.htm |date=October 27, 2007 }}, ''AAS/Division for Planetary Sciences Meeting Abstracts'', p. 53.07, September 1999</ref><ref>McHugh J.P. and Friedson A.J. 1996. Neptune's energy crisis: gravity wave heating of the stratosphere of Neptune. ''Bulletin of the American Astronomical Society'', p1078.</ref>

The structure inside Neptune is thought to be similar to the structure inside Uranus.<ref name=":8">Hubbard, W.B. 1997. Neptune's deep chemistry. ''Science''. '''275''' (5304): 1279–80.</ref> There is likely to be a [[planetary core|core]], thought to be about 1.5 Earth masses.<ref name="Hamilton">{{cite web | first=Calvin J. | last=Hamilton | date=August 4, 2001 | url=http://www.solarviews.com/eng/neptune.htm | title=Neptune |publisher=Views of the Solar System | accessdate=August 13, 2007}}</ref> It is made up of molten rock and metal surrounded by rock, water, ammonia, and methane.<ref name=Hamilton/> This mixture is referred to as icy. It is called a water-ammonia ocean.<ref>Atreya, S.; Egeler, P.; Baines, K. 2006. [https://www.cosis.net/abstracts/EGU06/05179/EGU06-J-05179-1.pdf Water-ammonia ionic ocean on Uranus and Neptune?] {{Webarchive|url=https://web.archive.org/web/20190918194516/https://www.cosis.net/abstracts/EGU06/05179/EGU06-J-05179-1.pdf |date=September 18, 2019 }} (PDF). ''Geophysical Research Abstracts''. '''8''', 05179.</ref> More mixtures of methane, ammonia, and water are found in the lower areas of the atmosphere.'''<ref name=":8" />''' At a depth of 7,000&nbsp;km of Neptune, the methane may decomposes into diamond crystals. These diamond crystals look like [[hailstone]]s.<ref>Kerr, Richard A. 1999. Neptune may crush methane into diamonds. ''Science''. '''286''' (5437): 25a–25.</ref><ref>{{Cite news|last=Kaplan|first=Sarah|date= 2017|title=It rains solid diamonds on Uranus and Neptune|language=en-US|newspaper=The Washington Post|url=https://www.washingtonpost.com/news/speaking-of-science/wp/2017/08/25/it-rains-solid-diamonds-on-uranus-and-neptune/|access-date=June 12, 2021|issn=0190-8286}}</ref>

{{multiple image
| align             = center
| direction         = horizontal
| header_align      = center
| header            = Neptune
| image1            = Neptune, Earth size comparison true color.jpg
| width1            = 268
| caption1          = Comparison of the size of Neptune and [[Earth]]
| image2            = Neptune-Int-color-corrected.jpg
| width2            = 270
| caption2          = Internal structure of Neptune
| image3            = Neptune_darkspot.jpg
| width3            = 153
| caption3          = The Great Dark Spot as seen from ''Voyager 2''
}}