Editing Planet (section)

== Planets in the Solar System ==

{{Main|Solar System}}
According to the [[IAU definition of planet|IAU definition]], there are eight planets in the Solar System, which are (in increasing distance from the Sun):<ref name="IAU"/> Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Jupiter is the largest, at 318 [[Earth mass]]es, whereas Mercury is the smallest, at 0.055 Earth masses.<ref name="JPL-physical-parameters">{{cite web |title=Planetary Physical Parameters |url=https://ssd.jpl.nasa.gov/planets/phys_par.html |url-status=live |archive-url=https://web.archive.org/web/20221004115344/https://ssd.jpl.nasa.gov/planets/phys_par.html |archive-date=4 October 2022 |access-date=11 July 2022 |website=Solar System Dynamics |publisher=Jet Propulsion Laboratory}}</ref>

The planets of the Solar System can be divided into categories based on their composition. [[Terrestrial planet|Terrestrials]] are similar to Earth, with bodies largely composed of [[Rock (geology)|rock]] and metal: Mercury, Venus, Earth, and Mars. Earth is the largest terrestrial planet.<ref name=Lewis59>{{cite book |first=John S. |last=Lewis |date=2004 |title=Physics and Chemistry of the Solar System |page=59 |edition=2nd |publisher=Academic Press |isbn=978-0-12-446744-6}}</ref> [[Giant planet]]s are significantly more massive than the terrestrials: Jupiter, Saturn, Uranus, and Neptune.<ref name=Lewis59/> They differ from the terrestrial planets in composition. The [[gas giant]]s, Jupiter and Saturn, are primarily composed of [[hydrogen]] and helium and are the most massive planets in the Solar System. Saturn is one third as massive as Jupiter, at 95 Earth masses.<ref name=M19>{{cite web |last1=Marley |first1=Mark |title=Not a Heart of Ice |date=2 April 2019 |url=https://www.planetary.org/articles/not-a-heart-of-ice |website=planetary.org |publisher=The Planetary Society |access-date=5 May 2022 |language=en |archive-date=12 August 2019 |archive-url=https://web.archive.org/web/20190812095448/http://www.planetary.org/blogs/guest-blogs/2019/not-a-heart-of-ice.html |url-status=live }}</ref> The [[ice giant]]s, Uranus and Neptune, are primarily composed of low-boiling-point materials such as water, [[methane]], and [[ammonia]], with thick atmospheres of hydrogen and helium. They have a significantly lower mass than the gas giants (only 14 and 17 Earth masses).<ref name=M19/>
[[File:Solar System true color (captions).jpg|center|thumb|600x600px|The Sun's, planets', dwarf planets' and moons' size to scale, labelled. Distance of objects is not to scale. The asteroid belt lies between the orbits of Mars and Jupiter, the Kuiper belt lies beyond Neptune's orbit.]]
Dwarf planets are gravitationally rounded, but have not cleared their orbits of other [[Small Solar System body|bodies]]. In increasing order of average distance from the Sun, the ones generally agreed among astronomers are {{dp|Ceres}}, {{dp|Orcus}}, {{dp|Pluto}}, {{dp|Haumea}}, {{dp|Quaoar}}, {{dp|Makemake}}, {{dp|Gonggong}}, {{dp|Eris}}, and {{dp|Sedna}}.<ref name=Grundy2019/><ref name=JWST/> Ceres is the largest object in the [[asteroid belt]], located between the orbits of Mars and Jupiter. The other eight all orbit beyond Neptune. Orcus, Pluto, Haumea, Quaoar, and Makemake orbit in the [[Kuiper belt]], which is a second belt of small Solar System bodies beyond the orbit of Neptune. Gonggong and Eris orbit in the [[scattered disc]], which is somewhat further out and, unlike the Kuiper belt, is unstable towards interactions with Neptune. Sedna is the largest known [[detached object]], a population that never comes close enough to the Sun to interact with any of the classical planets; the origins of their orbits are still being debated. All nine are similar to terrestrial planets in having a solid surface, but they are made of ice and rock rather than rock and metal. Moreover, all of them are smaller than Mercury, with Pluto being the largest known dwarf planet and Eris being the most massive.<ref name="Brown Schaller 2007">{{cite journal| doi = 10.1126/science.1139415| last1 = Brown| first1 = Michael E.| author-link = Michael E. Brown| last2 = Schaller| first2 = Emily L.| s2cid = 21468196| date = 15 June 2007| title = The Mass of Dwarf Planet Eris| journal = Science| volume = 316| issue = 5831| page = 1585| pmid = 17569855| bibcode = 2007Sci...316.1585B| url = http://hubblesite.org/pubinfo/pdf/2007/24/pdf.pdf| access-date = 27 September 2015| archive-url = https://web.archive.org/web/20160304053122/http://hubblesite.org/pubinfo/pdf/2007/24/pdf.pdf| archive-date = 4 March 2016}}</ref><ref>{{cite web |url=https://www.nasa.gov/feature/how-big-is-pluto-new-horizons-settles-decades-long-debate |title=How Big Is Pluto? New Horizons Settles Decades-Long Debate |website=NASA |date=7 August 2017 |access-date=5 May 2022 |archive-date=9 November 2019 |archive-url=https://web.archive.org/web/20191109182908/https://www.nasa.gov/feature/how-big-is-pluto-new-horizons-settles-decades-long-debate/ |url-status=dead }}</ref>

There are at least nineteen [[planetary-mass moon]]s or satellite planets—moons large enough to take on ellipsoidal shapes:<ref name=planetarysociety/>
* One satellite of Earth: the [[Moon]]
* Four [[Moons of Jupiter|satellites of Jupiter]]: [[Io (moon)|Io]], [[Europa (moon)|Europa]], [[Ganymede (moon)|Ganymede]], and [[Callisto (moon)|Callisto]]
* Seven [[Moons of Saturn|satellites of Saturn]]: [[Mimas (moon)|Mimas]], [[Enceladus]], [[Tethys (moon)|Tethys]], [[Dione (moon)|Dione]], [[Rhea (moon)|Rhea]], [[Titan (moon)|Titan]], and [[Iapetus (moon)|Iapetus]]
* Five [[Moons of Uranus|satellites of Uranus]]: [[Miranda (moon)|Miranda]], [[Ariel (moon)|Ariel]], [[Umbriel]], [[Titania (moon)|Titania]], and [[Oberon (moon)|Oberon]]
* One [[Moons of Neptune|satellite of Neptune]]: [[Triton (moon)|Triton]]
* One [[Moons of Pluto|satellite of Pluto]]: [[Charon (moon)|Charon]]

The Moon, Io, and Europa have compositions similar to the terrestrial planets; the others are made of ice and rock like the dwarf planets, with [[Tethys (moon)|Tethys]] being made of almost pure ice. Europa is often considered an icy planet, though, because its surface ice layer makes it difficult to study its interior.<ref name=planetarysociety/><ref>{{cite book |first=John S. |last=Lewis |date=2004 |title=Physics and Chemistry of the Solar System |page=425 |edition=2nd |publisher=Academic Press |isbn=978-0-12-446744-6}}</ref> Ganymede and Titan are larger than Mercury by radius, and Callisto almost equals it, but all three are much less massive. Mimas is the smallest object generally agreed to be a [[Geophysical definition of planet|geophysical planet]], at about six&nbsp;millionths of Earth's mass, though there are many larger bodies that may not be geophysical planets (e.g. {{dp|Salacia}}).<ref name=Grundy2019/>