Editing Solar System (section)

== Outer Solar System ==
The outer region of the Solar System is home to the [[giant planet]]s and their large moons. The [[Centaur (minor planet)|centaurs]] and many [[short-period comet]]s orbit in this region. Due to their greater distance from the Sun, the solid objects in the outer Solar System contain a higher proportion of volatiles such as water, ammonia, and methane, than planets of the inner Solar System because their lower temperatures allow these compounds to remain solid, without significant [[Sublimation (phase transition)|sublimation]].<ref name="bennett_8.2"/>

=== Outer planets ===
{{Main|Giant planet}}
[[File:Planet collage to scale (captioned).jpg|right|thumb|alt=Jupiter and Saturn is about 2 times bigger than Uranus and Neptune, 10 times bigger than Venus and Earth, 20 times bigger than Mars and 25 times bigger than Mercury|The outer planets [[Jupiter]], [[Saturn]], [[Uranus]] and [[Neptune]], compared to the inner planets Earth, Venus, Mars, and Mercury at the bottom right]]
The four outer planets, called giant planets or Jovian planets, collectively make up 99% of the mass orbiting the Sun.<ref group="lower-alpha" name="footnoteD" /> All four giant planets have multiple moons and a ring system, although only Saturn's rings are easily observed from Earth.<ref name="Ryden" /> Jupiter and Saturn are composed mainly of gases with extremely low melting points, such as hydrogen, helium, and [[neon]],<ref name="Podolak Podolak et al. 2000">{{Cite journal |last1=Podolak |first1=M. |last2=Podolak |first2=J. I. |last3=Marley |first3=M. S. |date=February 2000 |title=Further investigations of random models of Uranus and Neptune |url=https://zenodo.org/record/998024 |url-status=live |journal=Planetary and Space Science |volume=48 |issue=2–3 |pages=143–151 |bibcode=2000P&SS...48..143P |doi=10.1016/S0032-0633(99)00088-4 |archive-url=https://web.archive.org/web/20191221231229/https://zenodo.org/record/998024 |archive-date=21 December 2019 |access-date=25 August 2019 |ref={{SfnRef|Podolak Podolak et al.|2000}}}}</ref> hence their designation as [[gas giant]]s.<ref>{{Cite web |title=Gas Giant {{!}} Planet Types |url=https://exoplanets.nasa.gov/what-is-an-exoplanet/planet-types/gas-giant |url-status=live |archive-url=https://web.archive.org/web/20201128232046/https://exoplanets.nasa.gov/what-is-an-exoplanet/planet-types/gas-giant |archive-date=28 November 2020 |access-date=22 December 2020 |website=Exoplanet Exploration: Planets Beyond our Solar System|date=22 October 2020 }}</ref> Uranus and Neptune are [[ice giants]],<ref>{{Cite web |last1=Lissauer |first1=Jack J. |last2=Stevenson |first2=David J. |date=2006 |title=Formation of Giant Planets |url=http://www.gps.caltech.edu/uploads/File/People/djs/lissauer&stevenson(PPV).pdf |url-status=dead |archive-url=https://web.archive.org/web/20090326060004/http://www.gps.caltech.edu/uploads/File/People/djs/lissauer%26stevenson%28PPV%29.pdf |archive-date=26 March 2009 |access-date=16 January 2006 |website=NASA Ames Research Center; California Institute of Technology}}</ref> meaning they are largely composed of [[Volatile (astrogeology)|'ice' in the astronomical sense]] (chemical compounds with melting points of up to a few hundred [[kelvin]]s<ref name="Podolak Podolak et al. 2000" /> such as water, methane, ammonia, [[hydrogen sulfide]], and [[carbon dioxide]].<ref name="Podolak Weizman et al. 1995">{{Cite journal |last1=Podolak |first1=M. |last2=Weizman |first2=A. |last3=Marley |first3=M. |date=December 1995 |title=Comparative models of Uranus and Neptune |journal=Planetary and Space Science |volume=43 |issue=12 |pages=1517–1522 |bibcode=1995P&SS...43.1517P |doi=10.1016/0032-0633(95)00061-5 |ref={{SfnRef|Podolak Weizman et al.|1995}}}}</ref>) Icy substances comprise the majority of the satellites of the giant planets and small objects that lie beyond Neptune's orbit.<ref name="Podolak Weizman et al. 1995" /><ref name="zeilik">{{Cite book |last=Zellik |first=Michael |title=Astronomy: The Evolving Universe |date=2002 |publisher=[[Cambridge University Press]] |isbn=978-0-521-80090-7 |edition=9th |page=240 |oclc=223304585}}</ref>
* {{Visible anchor|Jupiter|text=[[Jupiter]]}} (4.95–5.46&nbsp;AU)<ref name="nasa-factsheet" group="D" /> is the biggest and most massive planet in the Solar System. On its surface, there are orange-brown and white cloud bands moving via the principles of [[atmospheric circulation]], with giant storms swirling on the surface such as the [[Great Red Spot]] and [[Oval BA|white 'ovals']]. [[Magnetosphere of Jupiter|Jupiter possesses a strong enough magnetosphere]] to redirect [[ionizing radiation]] and cause [[aurora]]s on its poles.<ref>{{Cite book |last=Rogers |first=John H. |url=https://books.google.com/books?id=SO48AAAAIAAJ&pg=PA293 |title=The giant planet Jupiter |date=1995 |publisher=Cambridge University Press |isbn=978-0521410083 |page=293 |access-date=13 April 2022 |archive-url=https://web.archive.org/web/20220420161219/https://www.google.com/books/edition/The_Giant_Planet_Jupiter/SO48AAAAIAAJ?gbpv=1&pg=PA293 |archive-date=20 April 2022 |url-status=live}}</ref> As of 2025, Jupiter has [[Moons of Jupiter|97 confirmed satellites]], which can roughly be sorted into three groups:
** The Amalthea group, consisting of [[Metis (moon)|Metis]], [[Adrastea (moon)|Adrastea]], [[Amalthea (moon)|Amalthea]], and [[Thebe (moon)|Thebe]]. They orbit substantially closer to Jupiter than other satellites.<ref>{{cite journal |last=Anderson |first=J.D. |author2=Johnson, T.V. |author3=Shubert, G. |display-authors=etal |date=2005 |title=Amalthea's Density Is Less Than That of Water |journal=Science |volume=308 |issue=5726 |pages=1291–1293 |bibcode=2005Sci...308.1291A |doi=10.1126/science.1110422 |pmid=15919987 |s2cid=924257}}</ref> Materials from these natural satellites are the source of Jupiter's faint ring.<ref>{{cite journal |author=Burns, J. A. |author2=Showalter, M. R. |author3=Hamilton, D. P. |display-authors=etal |date=1999 |title=The Formation of Jupiter's Faint Rings |journal=Science |volume=284 |issue=5417 |pages=1146–1150 |bibcode=1999Sci...284.1146B |doi=10.1126/science.284.5417.1146 |pmid=10325220 |s2cid=21272762}}</ref>
** The [[Galilean moons]], consisting of [[Ganymede (moon)|Ganymede]], [[Callisto (moon)|Callisto]], [[Io (moon)|Io]], and [[Europa (moon)|Europa]]. They are the largest moons of Jupiter and exhibit planetary properties.<ref>{{Cite web |last=Pappalardo |first=R. T. |date=1999 |title=Geology of the Icy Galilean Satellites: A Framework for Compositional Studies |url=http://www.agu.org/cgi-bin/SFgate/SFgate?&listenv=table&multiple=1&range=1&directget=1&application=fm99&database=%2Fdata%2Fepubs%2Fwais%2Findexes%2Ffm99%2Ffm99&maxhits=200&=%22P11C-10%22 |url-status=dead |archive-url=https://web.archive.org/web/20070930165551/http://www.agu.org/cgi-bin/SFgate/SFgate?&listenv=table&multiple=1&range=1&directget=1&application=fm99&database=%2Fdata%2Fepubs%2Fwais%2Findexes%2Ffm99%2Ffm99&maxhits=200&=%22P11C-10%22 |archive-date=30 September 2007 |access-date=16 January 2006 |website=Brown University}}</ref>
** Irregular satellites, consisting of substantially smaller natural satellites. They have more distant orbits than the other objects.<ref name="list">{{cite book |author=Sheppard, Scott S. |title=Jupiter. The planet, satellites and magnetosphere |author2=Jewitt, David C. |author3=Porco, Carolyn |date=2004 |publisher=Cambridge University Press |isbn=0-521-81808-7 |editor=Fran Bagenal |volume=1 |location=Cambridge, UK |pages=263–280 |chapter=Jupiter's outer satellites and Trojans |editor2=Timothy E. Dowling |editor3=William B. McKinnon |chapter-url=http://www.ifa.hawaii.edu/~jewitt/papers/JUPITER/JSP.2003.pdf |archive-url=https://web.archive.org/web/20090326065151/http://www.ifa.hawaii.edu/~jewitt/papers/JUPITER/JSP.2003.pdf |archive-date=26 March 2009 |url-status=dead}}</ref>
* {{Visible anchor|Saturn|text=[[Saturn]]}} (9.08–10.12&nbsp;AU)<ref name="nasa-factsheet" group="D" /> has a distinctive visible [[Rings of Saturn|ring system]] orbiting around its equator composed of small ice and rock particles. Like Jupiter, it is mostly made of hydrogen and helium.<ref>{{Cite web |date=18 August 2021 |title=In Depth: Saturn |url=https://solarsystem.nasa.gov/planets/saturn/in-depth |url-status=live |archive-url=https://web.archive.org/web/20180224210031/https://solarsystem.nasa.gov/planets/saturn/in-depth |archive-date=24 February 2018 |access-date=31 March 2022 |website=NASA Science: Solar System Exploration}}</ref> At its north and south poles, Saturn has peculiar [[Saturn's hexagon|hexagon-shaped storms]] larger than the diameter of Earth. [[Magnetosphere of Saturn|Saturn has a magnetosphere]] capable of producing weak auroras. As of 2025, Saturn has [[Moons of Saturn|274 confirmed satellites]], grouped into:
** Ring [[moonlet]]s and [[Shepherd moon|shepherds]], which orbit inside or close to Saturn's rings. A moonlet can only partially clear out dust in its orbit,<ref name="Sremcevic2007">{{cite journal |last1=Sremčević |first1=Miodrag |last2=Schmidt |first2=Jürgen |last3=Salo |first3=Heikki |last4=Seiß |first4=Martin |last5=Spahn |first5=Frank |last6=Albers |first6=Nicole |date=2007 |title=A belt of moonlets in Saturn's A ring |journal=[[Nature (journal)|Nature]] |volume=449 |issue=7165 |pages=1019–21 |bibcode=2007Natur.449.1019S |doi=10.1038/nature06224 |pmid=17960236 |s2cid=4330204}}</ref> while the ring shepherds are able to completely clear out dust, forming visible gaps in the rings.<ref name="Porco2005">{{cite journal |last1=Porco |first1=C. C. |last2=Baker |first2=E. |last3=Barbara |first3=J. |display-authors=etal |date=2005 |title=Cassini Imaging Science: Initial Results on Saturn's Rings and Small Satellites |url=http://ciclops.org/sci/docs/RingsSatsPaper.pdf |journal=Science |volume=307 |issue=5713 |pages=1234 |bibcode=2005Sci...307.1226P |doi=10.1126/science.1108056 |pmid=15731439 |s2cid=1058405 |access-date=21 April 2024 |archive-date=25 July 2011 |archive-url=https://web.archive.org/web/20110725171940/http://ciclops.org/sci/docs/RingsSatsPaper.pdf |url-status=live }}</ref>
** Inner large satellites [[Mimas]], [[Enceladus]], [[Tethys (moon)|Tethys]], and [[Dione (moon)|Dione]]. These satellites orbit within [[Rings of Saturn#E Ring|Saturn's E ring]]. They are composed mostly of water ice and are believed to have differentiated internal structures.<ref name=":2">{{Cite web |last=Williams |first=Matt |date=7 August 2015 |title=The moons of Saturn |url=https://phys.org/news/2015-08-moons-saturn.html |access-date=21 April 2024 |website=phys.org |language=en |archive-date=21 April 2024 |archive-url=https://web.archive.org/web/20240421075712/https://phys.org/news/2015-08-moons-saturn.html |url-status=live }}</ref>
** Trojan moons [[Calypso (moon)|Calypso]] and [[Telesto (moon)|Telesto]] (trojans of Tethys), and [[Helene (moon)|Helene]] and [[Polydeuces (moon)|Polydeuces]] (trojans of Dione). These small moons share their orbits with Tethys and Dione, leading or trailing either.<ref name="Calypso">{{cite web |publisher=NASA |url=https://science.nasa.gov/saturn/moons/calypso/ |title=Calypso |date=January 2024 |access-date=16 May 2024 |archive-date=17 May 2024 |archive-url=https://web.archive.org/web/20240517022857/https://science.nasa.gov/saturn/moons/calypso/ |url-status=live }}</ref><ref name="Polydeuces">{{cite web |publisher=NASA |url=https://science.nasa.gov/saturn/moons/polydeuces/ |title=Polydeuces |date=January 2024 |access-date=16 May 2024 }}</ref>
** Outer large satellites [[Rhea (moon)|Rhea]], [[Titan (moon)|Titan]], [[Hyperion (moon)|Hyperion]], and [[Iapetus (moon)|Iapetus]].<ref name=":2" /> Titan is the only satellite in the Solar System to have a substantial atmosphere.<ref name="Forget2017">{{cite journal |last1=Forget |first1=F. |last2=Bertrand |first2=T. |last3=Vangvichith |first3=M. |last4=Leconte |first4=J. |last5=Millour |first5=E. |last6=Lellouch |first6=E. |title=A post-New Horizons Global climate model of Pluto including the N 2, CH 4 and CO cycles |date=May 2017 |journal=Icarus |volume=287 |pages=54–71 |doi=10.1016/j.icarus.2016.11.038 |bibcode=2017Icar..287...54F|url=https://hal.sorbonne-universite.fr/hal-01427123/file/Forget_A_post-New_Horizons.pdf }}</ref>
** Irregular satellites, consisting of substantially smaller natural satellites. They have more distant orbits than the other objects. [[Phoebe (moon)|Phoebe]] is the largest irregular satellite of Saturn.<ref name="Jewitt2007"/>
* {{Visible anchor|Uranus|text=[[Uranus]]}} (18.3–20.1&nbsp;AU),<ref name="nasa-factsheet" group="D" /> uniquely among the planets, orbits the Sun on its side with an [[axial tilt]] >90°. This gives the planet extreme seasonal variation as each pole points alternately toward and then away from the Sun.<ref>{{Cite web |last=Devitt |first=Terry |date=14 October 2008 |title=New images yield clues to seasons of Uranus |publisher=University of Wisconsin–Madison |url=https://news.wisc.edu/new-images-yield-clues-to-seasons-of-uranus/ |access-date=6 April 2024 |archive-date=6 April 2024 |archive-url=https://web.archive.org/web/20240406210615/https://news.wisc.edu/new-images-yield-clues-to-seasons-of-uranus/ |url-status=live }}</ref> Uranus's outer layer has a muted [[cyan]] color, but underneath these clouds are [[Climate of Uranus|many mysteries about its climate]], such as unusually low [[internal heat]] and erratic cloud formation. As of 2025, Uranus has [[Moons of Uranus|28 confirmed satellites]], divided into three groups:
** Inner satellites, which orbit inside Uranus's ring system.<ref name="Esposito2002">{{cite journal |last=Esposito |first=L. W. |author-link=Larry W. Esposito |year=2002 |title=Planetary rings |journal=Reports on Progress in Physics |volume=65 |issue=12 |pages=1741–1783 |bibcode=2002RPPh...65.1741E |doi=10.1088/0034-4885/65/12/201 |s2cid=250909885}}</ref> They are very close to each other, which suggests that their orbits are [[Chaotic system|chaotic]].<ref name="Duncan Lissauer 1997">{{cite journal |last1=Duncan |first1=Martin J. |last2=Lissauer |first2=Jack J. |year=1997 |title=Orbital Stability of the Uranian Satellite System |journal=Icarus |volume=125 |issue=1 |pages=1–12 |bibcode=1997Icar..125....1D |doi=10.1006/icar.1996.5568}}</ref>
** Large satellites, consisting of [[Titania (moon)|Titania]], [[Oberon (moon)|Oberon]], [[Umbriel]], [[Ariel (moon)|Ariel]], and [[Miranda (moon)|Miranda]].<ref>{{Cite journal |last1=Sheppard |first1=S. S. |last2=Jewitt |first2=D. |last3=Kleyna |first3=J. |year=2005 |title=An Ultradeep Survey for Irregular Satellites of Uranus: Limits to Completeness |journal=The Astronomical Journal |volume=129 |issue=1 |page=518 |arxiv=astro-ph/0410059 |bibcode=2005AJ....129..518S |doi=10.1086/426329 |s2cid=18688556}}</ref> Most of them have roughly equal amounts of rock and ice, except Miranda, which is made primarily of ice.<ref name="Hussmann Sohl et al. 2006">{{cite journal |last1=Hussmann |first1=Hauke |last2=Sohl |first2=Frank |last3=Spohn |first3=Tilman |date=November 2006 |title=Subsurface oceans and deep interiors of medium-sized outer planet satellites and large trans-neptunian objects |journal=[[Icarus (journal)|Icarus]] |volume=185 |issue=1 |pages=258–273 |bibcode=2006Icar..185..258H |doi=10.1016/j.icarus.2006.06.005 |ref={{sfnRef|Hussmann Sohl et al.|2006}}}}</ref>
** Irregular satellites, having more distant and eccentric orbits than the other objects.<ref name="Sheppardmoons2024">{{cite web |date=23 February 2024 |title=New Uranus and Neptune Moons |url=https://sites.google.com/carnegiescience.edu/sheppard/home/newuranusneptunemoons |accessdate=23 February 2024 |work=Earth & Planetary Laboratory |publisher=Carnegie Institution for Science |archive-date=23 February 2024 |archive-url=https://web.archive.org/web/20240223160326/https://sites.google.com/carnegiescience.edu/sheppard/home/newuranusneptunemoons |url-status=live }}</ref>
* {{Visible anchor|Neptune|text=[[Neptune]]}} (29.9–30.5&nbsp;AU)<ref name="nasa-factsheet" group="D" /> is the furthest planet known in the Solar System. Its outer atmosphere has a slightly muted cyan color, with occasional storms on the surface that look like dark spots. Like Uranus, many atmospheric phenomena of Neptune are unexplained, such as the [[thermosphere]]'s abnormally high temperature or the strong tilt (47°) of its magnetosphere. As of 2025,  Neptune has [[Moons of Neptune|16 confirmed satellites]], divided into two groups:
** Regular satellites, which have circular orbits that lie near Neptune's equator.<ref name="Jewitt2007">{{cite journal |last=Jewitt |first=David |author2=Haghighipour, Nader |date=2007 |title=Irregular Satellites of the Planets: Products of Capture in the Early Solar System |url=http://www2.ess.ucla.edu/~jewitt/papers/2007/JH07.pdf |journal=Annual Review of Astronomy and Astrophysics |volume=45 |issue=1 |pages=261–95 |arxiv=astro-ph/0703059 |bibcode=2007ARA&A..45..261J |doi=10.1146/annurev.astro.44.051905.092459 |s2cid=13282788 |access-date=21 April 2024 |archive-date=25 February 2014 |archive-url=https://web.archive.org/web/20140225204338/http://www2.ess.ucla.edu/~jewitt/papers/2007/JH07.pdf |url-status=live }}</ref>
** Irregular satellites, which as the name implies, have less regular orbits. One of them, [[Triton (moon)|Triton]], is Neptune's largest moon. It is geologically active, with erupting [[geyser]]s of nitrogen gas, and possesses a thin, cloudy nitrogen atmosphere.<ref name="Soderblom2">{{Cite journal |last1=Soderblom |first1=L. A. |last2=Kieffer |first2=S. W. |last3=Becker |first3=T. L. |last4=Brown |first4=R. H. |last5=Cook |first5=A. F. II |last6=Hansen |first6=C. J. |last7=Johnson |first7=T. V. |last8=Kirk |first8=R. L. |last9=Shoemaker |first9=E. M. |author-link9=Eugene Merle Shoemaker |date=19 October 1990 |title=Triton's Geyser-Like Plumes: Discovery and Basic Characterization |url=https://www.geology.illinois.edu/~skieffer/papers/Truiton_Science_1990.pdf |url-status=live |journal=[[Science (journal)|Science]] |volume=250 |issue=4979 |pages=410–415 |bibcode=1990Sci...250..410S |doi=10.1126/science.250.4979.410 |pmid=17793016 |s2cid=1948948 |archive-url=https://web.archive.org/web/20210831121844/https://geology.illinois.edu/~skieffer/papers/Truiton_Science_1990.pdf |archive-date=31 August 2021 |access-date=31 March 2022}}</ref><ref name="Forget2017"/>

=== {{Anchor|Centaurs}}Centaurs ===
{{Main|Centaur (small Solar System body)|l1 = Centaur}}

The centaurs are icy, comet-like bodies whose [[Semi-major and semi-minor axes|semi-major axes]] are longer than Jupiter's and shorter than Neptune's (between 5.5 and 30&nbsp;AU). These are former Kuiper belt and [[Scattered disc|scattered disc objects]] (SDOs) that were gravitationally [[perturbation (astronomy)|perturbed]] closer to the Sun by the outer planets, and are expected to become comets or be ejected out of the Solar System.<ref name="Delsanti-Beyond_The_Planets" /> While most centaurs are inactive and asteroid-like, some exhibit cometary activity, such as the first centaur discovered, [[2060 Chiron]], which has been classified as a comet (95P) because it develops a coma just as comets do when they approach the Sun.<ref>{{Cite web |last=Vanouplines |first=Patrick |date=1995 |title=Chiron biography |url=http://www.vub.ac.be/STER/www.astro/chibio.htm |url-status=dead |archive-url=https://web.archive.org/web/20090502122306/http://www.vub.ac.be/STER/www.astro/chibio.htm |archive-date=2 May 2009 |access-date=23 June 2006 |website=Vrije Universitiet Brussel}}</ref> The largest known centaur, [[10199 Chariklo]], has a diameter of about {{Convert|250|km|abbr=on}} and is one of the few minor planets possessing a ring system.<ref name="spitzer">{{Cite conference |last1=Stansberry |first1=John |last2=Grundy |first2=Will |last3=Brown |first3=Mike |last4=Cruikshank |first4=Dale |last5=Spencer |first5=John |last6=Trilling |first6=David |last7=Margot |first7=Jean-Luc |date=2007 |title=Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope |page=161 |arxiv=astro-ph/0702538 |bibcode=2008ssbn.book..161S |book-title=The Solar System Beyond Neptune}}</ref><ref name="Braga-Ribas-2014">{{Cite journal |last=Braga-Ribas |first=F. |display-authors=etal |date=April 2014 |title=A ring system detected around the Centaur (10199) Chariklo |journal=[[Nature (journal)|Nature]] |volume=508 |issue=7494 |pages=72–75 |arxiv=1409.7259 |bibcode=2014Natur.508...72B |doi=10.1038/nature13155 |issn=0028-0836 |pmid=24670644 |s2cid=4467484}}</ref>