View source for Natural satellite

{{short description|Astronomical body that orbits a planet}}
{{About|the astronomical body|orbiting artificial spacecraft|Satellite}}
{{redirect|Moons|Earth's moon|Moon|other uses}}
{{Use dmy dates|date=November 2022}}
[[File:Dscovrepicmoontransitfull.gif|thumb|upright=1.35|The [[Moon]] orbiting around [[Earth]] (observed by the [[Deep Space Climate Observatory]])]]

A '''natural satellite''' is, in the most common usage, an [[astronomical object|astronomical body]] that [[orbit]]s a [[planet]], [[dwarf planet]], or [[small Solar System body]] (or sometimes another natural satellite). Natural satellites are colloquially referred to as '''moons''', a derivation from the [[Moon]] of [[Earth]].

In the [[Solar System]], there are six planetary [[Satellite system (astronomy)|satellite systems]], altogether comprising 419 natural satellites with confirmed orbits. Seven objects commonly considered [[dwarf planet]]s by astronomers are also known to have natural satellites: {{dp|Orcus}}, [[moons of Pluto|Pluto]], [[Moons of Haumea|Haumea]], {{dp|Quaoar}}, [[Makemake]], {{dp|Gonggong}}, and [[Eris (dwarf planet)|Eris]].<ref name="WGPSN"/> As of January 2022, there are 447 other [[Minor-planet moon|minor planets known to have natural satellites]].<ref name="Johnston"/>

==Terminology==
The first known natural satellite was the [[Moon]], but it was considered a "planet" until [[Nicolaus Copernicus|Copernicus]]' introduction of ''[[De revolutionibus orbium coelestium]]'' in 1543. Until the discovery of the [[Galilean moons|Galilean satellites]] in 1610 there was no opportunity for referring to such objects as a class. [[Galileo Galilei|Galileo]] chose to refer to his discoveries as ''Planetæ'' ("planets"), but later discoverers chose other terms to distinguish them from the objects they orbited.<ref name=metzger22>{{cite journal | title=Moons are planets: Scientific usefulness versus cultural teleology in the taxonomy of planetary science | last1=Metzger | first1=Philip T. | author-link1=Philip T. Metzger | last2=Grundy | first2=W. M. | first3=Mark V. | last3=Sykes | first4=Alan | last4=Stern | first5=James F. | last5=Bell III | first6=Charlene E. | last6=Detelich | first7=Kirby | last7=Runyon | first8=Michael | last8=Summers | year=2022 | journal=Icarus | volume=374 | article-number=114768 | doi=10.1016/j.icarus.2021.114768 | arxiv=2110.15285 | bibcode=2022Icar..37414768M | s2cid=240071005 }}</ref>

The first to use the term ''satellite'' to describe orbiting bodies was the German astronomer [[Johannes Kepler]] in his pamphlet ''Narratio de Observatis a se quatuor Iouis satellitibus erronibus'' ("Narration About Four Satellites of Jupiter Observed") in 1610. He derived the term from the [[Latin]] word ''satelles'', meaning "guard", "attendant", or "companion", because the ''satellites'' accompanied their primary planet in their journey through the heavens.<ref name="NASA-firstsatellites"/>

The term ''satellite'' thus became the normal one for referring to an object orbiting a planet, as it avoided the ambiguity of "moon". In 1957, however, the launching of the artificial object [[Sputnik]] created a need for new terminology.<ref name="NASA-firstsatellites"/> The terms ''man-made satellite'' and ''artificial moon'' were very quickly abandoned in favor of the simpler ''satellite''. As a consequence, the term has become linked with artificial objects flown in space.

Because of this shift in meaning, the term ''moon'', which had continued to be used in a generic sense in works of popular science and fiction, has regained respectability and is now used interchangeably with ''natural satellite'', even in scientific articles. When it is necessary to avoid both the ambiguity of confusion with Earth's natural satellite the Moon and the natural satellites of the other planets on the one hand, and artificial satellites on the other, the term ''natural satellite'' (using "natural" in a sense opposed to "artificial") is used. To further avoid ambiguity, the convention is to capitalize the word Moon when referring to Earth's natural satellite (a [[proper noun]]), but not when referring to other natural satellites ([[common noun]]s).

Many authors define "satellite" or "natural satellite" as orbiting some planet or minor planet, synonymous with "moon"&nbsp;– by such a definition all natural satellites are moons, but Earth and other planets are not satellites.<ref>{{cite book | first=Kenneth R. | last=Lang | date=3 Mar 2011 | page=15 | title=The Cambridge Guide to the Solar System | publisher=Cambridge University Press | isbn=978-1-139-49417-5 | url=https://books.google.com/books?id=S4xDhVCxAQIC&pg=PA15 | quote=Any object that orbits a planet is now called a satellite, and a natural satellite is also now called a moon }}</ref><ref>{{cite book | first1=Therese | last1=Encrenaz | author-link=Thérèse Encrenaz | first2=Jean-Pierre | last2=Bibring | first3=M. | last3=Blanc | first4=Maria-Antonietta | last4=Barucci | first5=Francoise | last5=Roques | first6=Philippe | last6=Zarka | title=The Solar System | year=2004 | page=30 | publisher=Springer Science & Business Media | isbn=978-3-540-00241-3 | translator-first=Storm | translator-last=Dunlop | url=https://books.google.com/books?id=Je61Y7UbqWgC&pg=PA30 }}</ref><ref>{{cite encyclopedia | 
editor1-first=Tilman | editor1-last=Spohn | editor2-first=Doris | editor2-last=Breuer | editor3-first=Torrence | editor3-last=Johnson | title=Encyclopedia of the Solar System | year=2014 | page=18 | publisher=Elsevier | isbn=978-0-12-416034-7 | url=https://books.google.com/books?id=0bEMAwAAQBAJ&pg=PA18 }}</ref> A few recent authors define "moon" as "a satellite of a planet or minor planet", and "planet" as "a satellite of a star"&nbsp;– such authors consider Earth as a "natural satellite of the Sun".<ref>{{cite book | title=Is Pluto a Planet?: A Historical Journey Through the Solar System | page=65 | first=David Andrew | last=Weintraub  | publisher=Princeton University Press | year=2007 | isbn=978-0-691-12348-6 | url=https://books.google.com/books?id=ELd-ve_35R8C&pg=PA65 | quote=... the general concept of a "moon" as a satellite of a planet and "planet" as a satellite of a star. }}</ref><ref>{{cite web | title=Satellite | url=http://www.merriam-webster.com/dictionary/satellite | website=www.merriam-webster.com | publisher=Merriam Webster | access-date=16 November 2015 }}</ref><ref name="NASA-what-is-a-satellite"/>

=== Definition of a moon ===
[[File:Moon, Earth size comparison.jpg|thumb|Size comparison of [[Earth]] and the [[Moon]]]]

There is no established lower limit on what is considered a "moon". Every natural celestial body with an identified orbit around a planet of the [[Solar System]], some as small as a kilometer across, has been considered a moon,<ref>{{cite book | last=Jaumann | first=R. | year=2011 | chapter=Satellite or Moon | editor1-last=Gargaud | editor1-first=M. | editor2-first=Ricardo | editor2-last=Amils | title=Encyclopedia of Astrobiology | page=1489 | publisher=Springer | location=Berlin, Heidelberg | doi=10.1007/978-3-642-11274-4_1403 | isbn=978-3-642-11271-3 }}</ref> though objects a tenth that size within Saturn's rings, which have not been directly observed, have been called ''[[moonlet]]s''. Small [[Minor-planet moon|asteroid moons]] (natural satellites of asteroids), such as [[Dactyl (moon)|Dactyl]], have also been called moonlets.<ref name="Marchis05">{{cite journal | first1=F. | last1=Marchis | title=Discovery of the triple asteroidal system 87 Sylvia | journal=Nature | volume=436 | pages=822–824 | year=2005 | bibcode=2005Natur.436..822M | doi=10.1038/nature04018 | pmid=16094362 | issue=7052 | last2=Descamps | first2=Pascal | last3=Hestroffer | first3=Daniel | last4=Berthier | first4=Jérome | s2cid=4412813 | url=https://escholarship.org/uc/item/7nb376hk}}</ref>

The upper limit is also vague. Two orbiting bodies are sometimes described as a [[double planet]] rather than a primary and satellite; the Earth-Moon system is used as an example.<ref>{{cite journal | title=Evolution of motion of a double planet in the gravitational field of a massive viscoelastic body | journal=Moscow University Mechanics Bulletin | last=Shatina | first=L. S. | volume=66 | pages=129–134 | date=December 2011 | issue=6 | doi=10.3103/S002713301106001X }}</ref> [[Asteroid]]s such as [[90 Antiope]] are considered double asteroids,<ref>{{cite journal | display-authors=1 | last1=Descamps | first1=P. | last2=Marchis | first2=F. | last3=Michalowski | first3=T. | last4=Vachier | first4=F. | last5=Colas | first5=F. | last6=Berthier | first6=J. | last7=Assafin | first7=M. | last8=Dunckel | first8=P. B. | last9=Polinska | first9=M. | last10=Pych | first10=W. | last11=Hestroffer | first11=D. | last12=Miller | first12=K. P. M. | last13=Vieira-Martins | first13=R. | last14=Birlan | first14=M. | last15=Teng-Chuen-Yu | first15=J.-P. | last16=Peyrot | first16=A. | last17=Payet | first17=B. | last18=Dorseuil | first18=J. | last19=Léonie | first19=Y. | last20=Dijoux | first20=T. | title=Figure of the double Asteroid 90 Antiope from adaptive optics and lightcurve observations | journal=Icarus | volume=187 | issue=2 | pages=482–499 |date=April 2007 | doi=10.1016/j.icarus.2006.10.030 | bibcode=2007Icar..187..482D }}</ref> but they have not forced a clear definition of what constitutes a moon. Some authors consider the Pluto–Charon system to be a double (dwarf) planet,<ref name=Ksanfomality_2016>{{cite journal | title=Pluto: Dwarf planet 134340 | last=Ksanfomality | first=L. V. | journal=Solar System Research | volume=50 | issue=1 | pages=67–80 | date=January 2016 | doi=10.1134/S0038094616010020  | bibcode=2016SoSyR..50...67K }}</ref> with one argument being that the [[barycentre]] lies above the surface of the larger body.<ref name=Rijsdijk_2007>{{cite journal | title=Pluto – when is a planet a planet? | first=Case | last=Rijsdijk | year=2007 | journal=Quest | volume=3 | issue=2 | pages=24–27 | url=https://journals.co.za/doi/pdf/10.10520/AJA1729830X_117 | access-date=2025-08-02 }}</ref> In contrast, the barycenter of all planetary moons of the Solar System are located within the radius of their host planet.<ref name=Hahn_2020>{{cite book | title=Basic Calculus of Planetary Orbits and Interplanetary Flight: The Missions of the Voyagers, Cassini, and Juno | first=Alexander J. | last=Hahn | publisher=Springer Nature | year=2020 | isbn=978-3-030-24868-0 | pages=120–121 | url=https://books.google.com/books?id=ILHWDwAAQBAJ&pg=PA120 }}</ref>

== Origin and orbital characteristics ==
{{further|Circumplanetary disk}}
The natural satellites orbiting relatively close to the planet on [[Retrograde and prograde motion|prograde]], uninclined circular orbits ([[regular moon|''regular'' satellites]]) are generally thought to have been formed out of the same [[Circumplanetary disk|collapsing region]] of the [[protoplanetary disk]] that created its primary.<ref name="arxiv0812">{{cite book | last1=Canup | first1=Robin M. | last2=Ward | first2=William R. |title=Origin of Europa and the Galilean Satellites |publisher=University of Arizona Press |date= 2008 |arxiv=0812.4995|bibcode = 2009euro.book...59C |page=59|isbn=978-0-8165-2844-8}}</ref><ref name=dangelo_podolak_2015>{{cite journal|last=D'Angelo|first=G.|author2= Podolak, M.|title=Capture and Evolution of Planetesimals in Circumjovian Disks|journal=The Astrophysical Journal|date=2015|volume=806|issue=1|pages=29–|doi=10.1088/0004-637X/806/2/203|arxiv = 1504.04364 |bibcode = 2015ApJ...806..203D |s2cid=119216797}}</ref> In contrast, [[irregular satellite]]s (generally orbiting on distant, [[orbital inclination|inclined]], [[orbital eccentricity|eccentric]] and/or [[retrograde motion|retrograde]] orbits) are thought to be captured [[asteroid]]s possibly further fragmented by collisions. Most of the major natural satellites of the Solar System have regular orbits, while most of the small natural satellites have irregular orbits.<ref>{{cite book | title=Encyclopedia of the Solar System | page=366 | publisher=Academic Press | year=2007 | first1=Lucy-Ann Adams | last1=McFadden | first2=Paul Robert | last2=Weissman | first3=Torrence V. | last3=Johnson | isbn=978-0-08-047498-4 }}</ref> The [[Moon]] and the [[Moons of Pluto]] are exceptions among large bodies in that they are thought to have originated from the collision of two large protoplanetary objects early in the Solar System's history (see the [[giant impact hypothesis]]).<ref>{{cite journal | last1 = Canup | first1 = R. M. | last2 = Asphaug | first2 = E. | title = Origin of the Moon in a giant impact near the end of the Earth's formation | journal = Nature | volume = 412 | pages = 708–712 | date = 2001 | doi = 10.1038/35089010 | pmid = 11507633 | issue = 6848 | bibcode=2001Natur.412..708C| s2cid = 4413525 }}</ref><ref>{{cite journal | title = A giant impact origin for Pluto's small natural satellites and satellite multiplicity in the Kuiper belt | last1 = Stern | first1 = S. A. | display-authors = 4 | last2 = Weaver | first2 = H. A. | last3 = Steffl | first3 = A. J. | last4 = Mutchler | first4 = M. J. | last5 = Merline | first5 = W. J. | last6 = Buie | first6 = M. W. | last7 = Young | first7 = E. F. | last8 = Young | first8 = L. A. | last9 = Spencer | first9 = J. R. | journal = Nature| volume = 439 | date = 2006 | pages = 946–49 | doi = 10.1038/nature04548 | pmid = 16495992 | issue = 7079|bibcode = 2006Natur.439..946S| s2cid = 4400037 }}</ref> The material that would have been placed in orbit around the central body is predicted to have reaccreted to form one or more orbiting natural satellites. As opposed to planetary-sized bodies, [[asteroid moon]]s are thought to commonly form by this process.<ref name=Durda_et_al_2004>{{cite journal | title=The formation of asteroid satellites in large impacts: results from numerical simulations | display-authors=1 | last1=Durda | first1=Daniel D. | last2=Bottke | first2=William F. | last3=Enke | first3=Brian L. | last4=Merline | first4=William J. | last5=Asphaug | first5=Erik | last6=Richardson | first6=Derek C. | last7=Leinhardt | first7=Zoë M. | journal=Icarus | volume=167 | issue=2 | pages=382–396 | date=February 2004 | doi=10.1016/j.icarus.2003.09.017 | bibcode=2004Icar..167..382D }}</ref> [[Triton (moon)|Triton]] is another exception; although large and in a close, circular orbit, its motion is retrograde and it is thought to be a captured [[dwarf planet]].<ref>{{Cite journal | title=Neptune's capture of its moon Triton in a binary–planet gravitational encounter | journal=Nature | volume=441 | issue=7090 | pages=192–4 | year=2006 | last1=Agnor | first1=C. B. | last2=Hamilton | first2=D. P. | doi=10.1038/nature04792 | pmid=16688170| bibcode=2006Natur.441..192A| s2cid=4420518 }}</ref>

=== Trojan satellites ===

Two natural satellites are known to have small companions at both their {{L4}} and {{L5}} [[Lagrangian point]]s, sixty degrees ahead and behind the body in its orbit. These companions are called [[trojan moon]]s, as their orbits are analogous to the [[trojan asteroid]]s of [[Jupiter]]. The trojan moons are [[Telesto (moon)|Telesto]] and [[Calypso (moon)|Calypso]], which are the leading and following companions, respectively, of the Saturnian moon [[Tethys (moon)|Tethys]]; and [[Helene (moon)|Helene]] and [[Polydeuces (moon)|Polydeuces]], the leading and following companions of the Saturnian moon [[Dione (moon)|Dione]].<ref>{{cite journal | title=Photometric Analyses of Saturn's Small Moons: Aegaeon, Methone, and Pallene Are Dark; Helene and Calypso Are Bright | last1=Hedman | first1=M. M. | last2=Helfenstein | first2=P. | last3=Chancia | first3=R. O. | last4=Thomas | first4=P. | last5=Roussos | first5=E. | last6=Paranicas | first6=C. | last7=Verbiscer | first7=A. J. | journal=The Astronomical Journal | volume=159 | issue=4 | at=id. 129 | date=April 2020 | doi=10.3847/1538-3881/ab659d | doi-access=free | arxiv=1912.09192 | bibcode=2020AJ....159..129H }}</ref>

=== Temporary satellites ===
{{Main|Temporary satellite}}
The capture of an asteroid from a heliocentric orbit is not always permanent. According to simulations, [[temporary satellite]]s should be a common phenomenon.<ref name="Carlisle">{{cite news | first=Camille M. | last=Carlisle |title=Pseudo-moons Orbit Earth |work=Sky & Telescope |date=30 December 2011 }}</ref><ref name="Fedorets">{{cite journal |last1=Fedorets |first1=Grigori |last2=Granvik |first2=Mikael |last3=Jedicke |first3=Robert |title=Orbit and size distributions for asteroids temporarily captured by the Earth-Moon system |journal=Icarus |volume=285 |pages=83–94 |date=15 March 2017 |doi=10.1016/j.icarus.2016.12.022 |bibcode=2017Icar..285...83F }}</ref> {{asof|2023}}, the observed minor bodies that have displayed transient co-orbital motion with Earth are: {{mpl|1991 VG}}, {{mpl|2006 RH|120}}, {{mpl|2020 CD|3}}, and {{mpl|2022 NX|1}}.<ref>{{cite journal | last1=Leon | first1=J. D. | last2=Licandro Goldaracena | first2=J. | last3=Serra-Ricart | first3=M. | last4=Cabrera-Lavers | first4=A. | year=2023 | title=Mini-moons from horseshoes: A physical characterization of 2022 NX1 with OSIRIS at the 10.4 m Gran Telescopio Canarias | journal=Astronomy & Astrophysics | volume=670 | page=L10 | doi=10.1051/0004-6361/202245514 | arxiv=2301.10797 }}</ref>

{{mpl|2006 RH|120}} was a temporary satellite of Earth for nine months in 2006 and 2007.<ref name="Shefford">{{cite web |url=http://www.birtwhistle.org/Gallery6R10DB9.htm |title=2006 RH120 ( = 6R10DB9) (A second moon for the Earth?) |publisher=Great Shefford Observatory |date=14 September 2017 |access-date=13 November 2017 |url-status=live |archive-url=https://web.archive.org/web/20150206154817/http://www.birtwhistle.org/Gallery6R10DB9.htm |archive-date=6 February 2015 }}</ref><ref name="Sinott">{{cite news |title=Earth's "Other Moon" |work=Sky & Telescope | first=Roger W.| last= Sinnott |date=17 April 2007 |url=http://www.skyandtelescope.com/news/7067527.html |url-status=dead |archive-url=https://web.archive.org/web/20120402120646/http://www.skyandtelescope.com/news/7067527.html |archive-date=2 April 2012 |access-date=12 March 2018 }}</ref>

== Tidal locking ==
{{main|Tidal locking}}

Most [[regular moon]]s (natural satellites following relatively close and prograde orbits with small orbital inclination and eccentricity) in the Solar System are tidally locked to their respective primaries, meaning that the same side of the natural satellite always faces its planet. This phenomenon comes about through a loss of energy due to tidal forces raised by the planet, slowing the rotation of the satellite until it is negligible.<ref name=Barnes_2010>{{cite book | title=Formation and Evolution of Exoplanets | editor1-first=Rory | editor1-last=Barnes | publisher=John Wiley & Sons | year=2010 | isbn=978-3-527-40896-2 | page=248 | url=https://books.google.com/books?id=-7KimFtJnIAC&pg=PA248 }}</ref> Exceptions are known; one such exception is [[Saturn]]'s natural satellite [[Hyperion (moon)|Hyperion]], which rotates chaotically because of the gravitational influence of [[Titan (moon)|Titan]].<ref>{{cite journal | title=Influence of a second satellite on the rotational dynamics of an oblate moon | first=M. | last=Tarnopolski | journal=Celestial Mechanics and Dynamical Astronomy | volume=127 | issue=2 | pages=121–138 | date=Feb 2017 | doi=10.1007/s10569-016-9719-7|bibcode=2017CeMDA.127..121T | arxiv=1607.07333 | s2cid=118512400 }}</ref> Pluto's four, circumbinary small moons also rotate chaotically due to Charon's influence.<ref name="NASA2015"/>

In contrast, the outer natural satellites of the giant planets (irregular satellites) are too far away to have become locked. For example, Jupiter's [[Himalia (moon)|Himalia]], Saturn's [[Phoebe (moon)|Phoebe]], and Neptune's [[Nereid (moon)|Nereid]] have rotation periods in the range of ten hours, whereas their orbital periods are hundreds of days.<ref>{{cite journal | title=The rotation states predominant among the planetary satellites | last1=Melnikov | first1=A. V. | last2=Shevchenko | first2=I. I. | journal=Icarus | volume=209 | issue=2 | pages=786–794 | date=October 2010 | doi=10.1016/j.icarus.2010.04.022 | arxiv=1312.5236 | bibcode=2010Icar..209..786M }}</ref>

== Satellites of satellites ==
{{Main|Subsatellite}}
[[File:Rhean rings PIA10246 Full res.jpg|thumb|Artist impression of [[Rhea (moon)|Rhea]]'s proposed rings]]

No "moons of moons" or subsatellites (natural satellites that orbit a natural satellite of a planet) are currently known. In most cases, the tidal effects of the planet would make such a system unstable. Potential exceptions include large moons on wide orbits, including Titan, Iapetus, Callisto, and the Moon. However, other sources of dynamical instability may remove such submoons, such as [[Mass_concentration_(astronomy)|mascons]] on the Moon.<ref>{{cite journal
 | title=Can moons have moons?
 | last1=Kollmeier | first1=Juna A. | last2=Raymond | first2=Sean N.
 | journal=Monthly Notices of the Royal Astronomical Society: Letters
 | volume=483 | issue=1 | pages=L80–L84 | date=February 2019
 | doi=10.1093/mnrasl/sly219 | doi-access=free | arxiv=1810.03304
 | bibcode=2019MNRAS.483L..80K }}</ref>

Calculations performed after the 2008 detection<ref>
{{cite journal
| last1 = Jones | first1 = G. H.
| display-authors = etal
| year = 2008
| title = The Dust Halo of Saturn's Largest Icy Moon, Rhea – Jones et al. 319 (5868): 1380 – Science
| journal = Science
| volume = 319 | issue = 5868 | pages = 1380–1384
| bibcode = 2008Sci...319.1380J
| doi = 10.1126/science.1151524
| pmid = 18323452
| s2cid = 206509814
| url = https://pdfs.semanticscholar.org/0d74/d7801493544d2f60b90f17c64d89fcf8594e.pdf | archive-url = https://web.archive.org/web/20180308165130/https://pdfs.semanticscholar.org/0d74/d7801493544d2f60b90f17c64d89fcf8594e.pdf | url-status = dead | archive-date = 2018-03-08 }}</ref> of a possible [[Rings of Rhea|ring system]] around Saturn's moon [[Rhea (moon)|Rhea]] indicate that satellites orbiting Rhea could have stable orbits. Furthermore, the suspected rings are thought to be narrow,<ref>{{cite web
|url=https://www.newscientist.com/article/dn13421-saturn-satellite-reveals-first-moon-rings/
|title=Saturn satellite reveals first moon rings |date= 6 March 2008 |work= New Scientist
|first=Jeff | last=Hecht
}}</ref> a phenomenon normally associated with [[shepherd moon]]s. However, targeted images taken by the ''[[Cassini–Huygens|Cassini]]'' spacecraft failed to detect rings around Rhea.<ref>{{cite journal|title=Cassini imaging search rules out rings around Rhea – Tiscareno – 2010 |journal= Geophysical Research Letters|volume=37 |issue=14 |pages=n/a | doi = 10.1029/2010GL043663 | arxiv = 1008.1764|bibcode=2010GeoRL..3714205T|year = 2010|last1 = Tiscareno|first1 = Matthew S.|last2=Burns |first2=Joseph A. |last3=Cuzzi |first3=Jeffrey N. |last4=Hedman |first4=Matthew M. |s2cid= 133143673}}</ref>

It has also been proposed that Saturn's moon [[Iapetus (moon)|Iapetus]] had a satellite in the past; this is one of several hypotheses that have been put forward to account for its [[Equatorial ridge on Iapetus|equatorial ridge]].<ref>{{cite web | url=https://source.wustl.edu/2010/12/how-iapetus-saturns-outermost-moon-got-its-ridge/ | first=Tony | last=Fitzpatrick | date=13 December 2010 | title=How Iapetus, Saturn's outermost moon, got its ridge | publisher=Washington University in St. Louis | access-date=2025-08-03 }}</ref>

Light-curve analysis suggests that Saturn's irregular satellite [[Kiviuq (moon)|Kiviuq]] is extremely prolate, and is likely a [[Contact binary (small Solar System body)|contact binary]] or even a binary moon.<ref name="LPSC2654">{{cite conference
  |title=Cassini Observations of Saturn's Irregular Moons
  |url=https://www.hou.usra.edu/meetings/lpsc2019/pdf/2654.pdf
  |first1=T. |last1=Denk
  |first2=S. |last2=Mottola
  |conference=50th Lunar and Planetary Science Conference
  |publisher=Lunar and Planetary Institute
  |number=2132
  |year=2019}}</ref>

== Shape ==
{{see also|Satellite planet}}
<!--Linked from [[Template:Infobox planetary system]]-->
[[File:Masses of all moons.png|thumb|300px|The relative masses of the natural satellites of the [[Solar System]]. [[Mimas (moon)|Mimas]], [[Enceladus]], and [[Miranda (moon)|Miranda]] are too small to be visible at this scale. All the irregularly shaped natural satellites, even added together, would also be too small to be visible.]]

Neptune's moon [[Proteus (moon)|Proteus]] is the largest irregularly shaped natural satellite, and is about as large as an icy moon can become before becoming [[Relaxation (physics)|relaxed]] into a [[spheroid]]al shape.<ref name=Croft_402>{{cite journal | title=Proteus: Geology, shape, and catastrophic destruction | last=Croft | first=Steven K. | journal=Icarus | volume=99 | issue=2 | pages=402–419 | date=October 1992 | doi=10.1016/0019-1035(92)90156-2 | bibcode=1992Icar...99..402C }}</ref> The shapes of moons in synchronous orbit are expected to [[Asymptote|asymptotically]] change shape into rounded [[ellipsoid]]s under [[hydrostatic equilibrium]], although this may not happen in the age of the Solar System. For example, the larger Saturnian moons are in equilibrium, while [[Iapetus (moon)|Iapetus]], Mimas, and Enceladus are apparently not.<ref>{{cite journal | title=Multi-layer Hydrostatic Equilibrium of Planets and Synchronous Moons: Theory and Application to Ceres and to Solar System Moons | last=Tricarico | first=Pasquale | journal=The Astrophysical Journal | volume=782 | issue=2 | at=id. 99 | date=February 2014 | doi=10.1088/0004-637X/782/2/99 | arxiv=1312.7427 | bibcode=2014ApJ...782...99T }}</ref><ref>{{cite journal | title=The tidal history of Iapetus: Spin dynamics in the light of a refined dissipation model | last1=Castillo-Rogez | first1=Julie C. | last2=Efroimsky | first2=Michael | last3=Lainey | first3=Valéry | journal=Journal of Geophysical Research | volume=116 | issue=E9 | at=ID E09008 | date=September 2011 | doi=10.1029/2010JE003664 | bibcode=2011JGRE..116.9008C | url=https://hal.science/hal-03786012 }}</ref> {{citation needed span|date=August 2025|The "round/rounded satellites" are sometimes categorized as [[planetary-mass moon]]s.}} The shapes of Eris' moon [[Dysnomia (moon)|Dysnomia]] and {{dp|Orcus}}' moon [[Vanth (moon)|Vanth]] are presently unknown, although Dysnomia's density is high enough that it is probably a solid ellipsoid as well.{{cn|date=August 2025}}

The larger natural satellites, being tidally locked, tend toward [[Oval|ovoid]] (egg-like) shapes: squat at their poles and with longer equatorial axes in the direction of their primaries (their planets) than in the direction of their motion.<ref name=Rambaux_Castillo-Rogez_2012/>{{rp|pp=184–187}} Saturn's moon [[Mimas (moon)|Mimas]], for example, has a major axis 9% greater than its polar axis and 5% greater than its other equatorial axis.<ref name=Thomas_2010>{{cite journal | title=Sizes, shapes, and derived properties of the saturnian satellites after the Cassini nominal mission | last=Thomas | first=P. C. | journal=Icarus | date=July 2010 | volume=208 | issue=1 | pages=395–401 | doi=10.1016/j.icarus.2010.01.025 | bibcode=2010Icar..208..395T | url=https://ciclops.org/media/sp/2011/6794_16344_0.pdf | access-date=2025-08-03 }}</ref> [[Methone (moon)|Methone]], another of Saturn's moons, is only around 3&nbsp;km in diameter and [[:File:Methone PIA14633.jpg|visibly egg-shaped]].<ref>{{cite conference | title=Methone as an icy cosmic model of Earth | last=Kochemasov | first=G. G. | conference=European Planetary Science Congress 2013, held 8-13 September in London, UK | date=September 2013 | bibcode=2013EPSC....8..148K }}</ref> The effect is smaller on the largest natural satellites, where their gravity is greater relative to the effects of tidal distortion, especially those that orbit less massive planets or, as in the case of the Moon, at greater distances.<ref name=Rambaux_Castillo-Rogez_2012>{{cite book | chapter=Tides on Satellites of Giant Planets | first1=Nicolas | last1=Rambaux | first2=Julie | last2=Castillo-Rogez | title=Tides in Astronomy and Astrophysics | volume=861 | series=Lecture Notes in Physics | editor1-first=Jean | editor1-last=Souchay | editor2-first=Stéphane | editor2-last=Mathis | editor3-first=Tadashi | editor3-last=Tokieda | publisher=Springer | year=2012 | isbn=978-3-642-32961-6 | chapter-url=https://books.google.com/books?id=jIm5BQAAQBAJ&pg=PA170 }}</ref>{{rp|pp=167–170}}
{| class="wikitable" style="font-size: 0.9em;"
! rowspan="2" width=120 | Name
! rowspan="2" | Satellite of
! colspan="2" | Difference in axes
|-
! km
! {{longitem|% of [[mean diameter]]}}
|-
| [[Mimas (moon)|Mimas]] || [[Saturn]] || 33.4<ref name=Thomas_2010/> {{smaller|(20.4{{\}}13.0)}} || 8.4 {{smaller|(5.1{{\}}3.3)}}
|-
| [[Enceladus]] || Saturn || 16.6<ref name=Thomas_2010/> || 3.3
|-
| [[Miranda (moon)|Miranda]] || [[Uranus]] || 14.2 || 3.0
|-
| [[Tethys (moon)|Tethys]] || Saturn || 25.8<ref name=Thomas_2010/> || 2.4
|-
| [[Io (moon)|Io]] || [[Jupiter]] || 29.4 || 0.8
|-
| [[Moon|Luna]] || [[Earth]] || 4.3 || 0.1
|}

==Geological activity==
Of the nineteen known natural satellites in the Solar System that are large enough to be gravitationally rounded, several remain geologically active today. [[Io (moon)|Io]] is the most volcanically active body in the Solar System,<ref name=Lainey_et_al_2009>{{cite journal | title=Strong tidal dissipation in Io and Jupiter from astrometric observations | last1=Lainey | first1=Valery | last2=Arlot | first2=J. | last3=Karatekin | first3=O. | last4=Van Hoolst | first4=T. | journal=Nature | volume=459 | issue=957–959 | year=2009 | pages=957–959 | doi=10.1038/nature08108 | pmid=19536258 | bibcode=2009Natur.459..957L }}</ref> while [[Europa (moon)|Europa]],<ref name=Cook_et_al_2013>{{cite web | last1=Cook | first1=Jia-Rui C. | last2=Gutro | first2=Rob | last3=Brown | first3=Dwayne | last4=Harrington | first4=J. D. | last5=Fohn | first5=Joe | title=Hubble Sees Evidence of Water Vapor at Jupiter Moon | url=http://www.jpl.nasa.gov/news/news.php?release=2013-363 | date=12 December 2013 | publisher=NASA JPL | access-date=12 December 2013 }}</ref> [[Enceladus]],<ref name=Roberts_Nimmo_2008>{{cite journal | title=Tidal heating and the long-term stability of a subsurface ocean on Enceladus | last1=Roberts | first1=James H. | last2=Nimmo | first2=Francis | journal=Icarus | volume=194 | issue=2 | pages=675–689 | date=April 2008  | doi=10.1016/j.icarus.2007.11.010 | bibcode=2008Icar..194..675R }}</ref> and [[Triton (moon)|Triton]] display evidence of ongoing [[Tectonics|tectonic activity]] and [[Cryovolcano|cryovolcanism]]. In the first three cases, the geological activity is powered by the [[Tidal heating#Tidal heating|tidal heating]] resulting from having [[orbital eccentricity|eccentric orbits]] close to their giant-planet primaries.<ref name=Lainey_et_al_2009/><ref name=Cook_et_al_2013/><ref name=Roberts_Nimmo_2008/> (This mechanism would have also operated on Triton in the past before its orbit was [[tidal circularization|circularized]].<ref>{{cite journal | title=The coupled orbital and thermal evolution of Triton | last1=Ross | first1=M. N. | last2=Schubert | first2=G. | journal=Geophysical Research Letters | date=September 1990 | volume=17 | issue=10 | pages=1749–1752 | doi=10.1029/GL017i010p01749 | bibcode=1990GeoRL..17.1749R | doi-access=free }}</ref>) Many other natural satellites, such as Earth's Moon, [[Ganymede (moon)|Ganymede]], [[Titan (moon)|Titan]], Tethys, and Miranda show evidence of past geological activity, resulting from energy sources such as the [[Radioactive decay|decay]] of their [[Primordial nuclide|primordial]] [[Radionuclide|radioisotopes]], greater past orbital eccentricities (due in some cases to past [[orbital resonance]]s), or the [[Planetary differentiation|differentiation]] or freezing of their interiors.<ref name=Nimmo_2025/> Enceladus and Triton both have active features resembling [[geysers]], although in the case of Triton solar heating appears to provide the energy. Titan and Triton have significant atmospheres; Titan also has [[lakes of Titan|hydrocarbon lakes]].<ref name=Nimmo_2025>{{cite journal | title=Surfaces, interiors and evolution of solar system moons | last=Nimmo | first=F. | journal=Proceedings of the Royal Society A | volume=481 | issue=2312 | at=id. 20240806 | date=April 2025 | article-number=20240806 | doi=10.1098/rspa.2024.0806 | bibcode=2025RSPSA.48140806N | doi-access=free }}</ref> All four of the Galilean moons have atmospheres, though they are extremely thin.<ref>{{Cite web | url=https://www.planetary.org/blogs/emily-lakdawalla/2015/04081101-a-moon-with-atmosphere.html | title=A moon with atmosphere | first=Emily | last=Lakdawalla | publisher=The Planetary Society | date=8 April 2015 | access-date=24 December 2019 | archive-date=24 December 2019 | archive-url=https://web.archive.org/web/20191224075248/https://www.planetary.org/blogs/emily-lakdawalla/2015/04081101-a-moon-with-atmosphere.html | url-status=live }}</ref><ref name="EuropaAtmosphere">{{Cite web |title=Hubble Finds Oxygen Atmosphere on Jupiter's Moon, Europa |url=http://hubblesite.org/contents/news-releases/1995/news-1995-12 |access-date=2022-05-13 |website=HubbleSite.org |language=en |archive-date=16 April 2023 |archive-url=https://web.archive.org/web/20230416151919/https://hubblesite.org/contents/news-releases/1995/news-1995-12.html |url-status=live }}</ref><ref name="JPLAtmosphere">{{cite web |archive-url= https://web.archive.org/web/20090504072525/http://www2.jpl.nasa.gov/galileo/hst7.html |url= http://www2.jpl.nasa.gov/galileo/hst7.html|title=Hubble Finds Thin Oxygen Atmosphere on Ganymede |work=Jet Propulsion Laboratory |publisher=NASA |date=October 23, 1996 |access-date= February 17, 2017|url-status= dead |archive-date= May 4, 2009}}</ref> Four of the largest natural satellites, Europa,<ref name=Cook_et_al_2013/> Ganymede, [[callisto (moon)|Callisto]], and Titan, are thought to have subsurface oceans of liquid water,<ref name=Nimmo_2025/> while smaller Enceladus also supports a global subsurface ocean of liquid water.<ref name=Roberts_Nimmo_2008/>

== Occurrence in the Solar System ==
[[File:Moons of the Solar System To Scale (43564841545).png|thumb|330px|right|Largest moons to scale with their parent planets and dwarf planet]]
Of the inner planets, [[Mercury (planet)|Mercury]] and [[Venus]] have no natural satellites; Earth has one large natural satellite, known as the Moon; and [[Mars]] has two tiny natural satellites, [[Phobos (moon)|Phobos]] and [[Deimos (moon)|Deimos]]. The [[giant planet]]s have extensive systems of natural satellites, including half a dozen comparable in size to Earth's Moon: the four [[Galilean moon]]s, Saturn's Titan, and [[Neptune]]'s Triton.<ref name=Kane_et_al_2013>{{cite journal | title=Solar System Moons as Analogs for Compact Exoplanetary Systems | last1=Kane | first1=Stephen R. | last2=Hinkel | first2=Natalie R. | last3=Raymond | first3=Sean N. | journal=The Astronomical Journal | volume=146 | issue=5 | at=id. 122 | date=November 2013 | doi=10.1088/0004-6256/146/5/122 | arxiv=1309.1467 | bibcode=2013AJ....146..122K }}</ref> Saturn has an additional six mid-sized natural satellites massive enough to have achieved [[hydrostatic equilibrium]], and [[Uranus]] has five. It has been suggested that some [[Natural satellite habitability|satellites may potentially harbour life]].<ref name="WRD-20150127">{{cite journal |last=Woo |first=Marcus |title=Why We're Looking for Alien Life on Moons, Not Just Planets |url=https://www.wired.com/2015/01/looking-alien-life-moons-just-planets/ |date=27 January 2015 |journal=[[Wired (website)|Wired]] |access-date=27 January 2015}}</ref>

Among the objects generally agreed by astronomers to be dwarf planets, [[Ceres (dwarf planet)|Ceres]] and {{dp|Sedna}} have no known natural satellites. Pluto has the relatively large natural satellite Charon and four smaller natural satellites; [[Styx (moon)|Styx]], [[Nix (moon)|Nix]], [[Kerberos (moon)|Kerberos]], and [[Hydra (moon)|Hydra]].<ref name="esahubble">{{cite news | title=Hubble Discovers New Pluto Moon | url=http://www.spacetelescope.org/news/heic1212/ | access-date=13 July 2012 | newspaper=ESA/Hubble Press Release }}</ref> [[Haumea]] has two natural satellites; {{dp|Orcus}}, {{dp|Quaoar}}, [[Makemake]], {{dp|Gonggong}}, and {{dp|Eris}} have one each.<ref name=Upadhyay_2025>{{cite book | title=Geology and Mineral Resources | series=Springer Geology | first=R. K. | last=Upadhyay | publisher=Springer Nature | year=2025 | isbn=978-981-96-0598-9 | pages=16–17 | url=https://books.google.com/books?id=tNM9EQAAQBAJ&pg=PA16 }}</ref> The Pluto–Charon system is unusual in that the [[center of mass#Barycenter in astrophysics and astronomy|center of mass]] lies in open space between the two, a characteristic sometimes associated with a [[double planet|double-planet]] system.<ref name=Ksanfomality_2016/>

Planets around other stars are likely to have satellites as well, and although numerous candidates have been detected to date, {{asof|2024|lc=y}} none have yet been confirmed.<ref>{{cite journal | title=The spectroastrometric detectability of nearby Solar System-like exomoons | last1=van Woerkom | first1=Q. B. | last2=Kleisioti | first2=E. | journal=Astronomy & Astrophysics | volume=684 | at=id. A72 | date=April 2024 | doi=10.1051/0004-6361/202348604 | arxiv=2402.07517 | bibcode=2024A&A...684A..72V }}</ref>

=== Non-planetary satellites ===
{{main|Asteroid moon}}

The discovery of [[243 Ida]]'s natural satellite [[Dactyl (moon)|Dactyl]] in the early 1990s confirmed that some [[asteroid]]s have natural satellites;<ref>{{cite journal | title=Bulk density of asteroid 243 Ida from the orbit of its satellite Dactyl | last1=Belton | first1=M. J. S. | last2=Chapman | first2=C. R. | last3=Thomas | first3=P. C. | last4=Davies | first4=M. E. | last5=Greenberg | first5=R. | last6=Klaasen | first6=K. | last7=Byrnes | first7=D. | last8=D'Amario | first8=L. | last9=Synnott | first9=S. | last10=Johnson | first10=T. V. | last11=McEwen | first11=A. | last12=Merline | first12=W. J. | last13=Davis | first13=D. R. | last14=Petit | first14=J. -M. | last15=Storrs | first15=A. | last16=Veverka | first16=J. | last17=Zellner | first17=B. | journal=Nature | volume=374 | issue=6525 | pages=785–788 | date=April 1995 | doi=10.1038/374785a0 | bibcode=1995Natur.374..785B }}</ref> indeed, [[87 Sylvia]] has two.<ref>{{cite journal | title=Instability zones for satellites of asteroids: The example of the (87) Sylvia system | last1=Frouard | first1=Julien | last2=Compère | first2=Audrey | journal=Icarus | volume=220 | issue=1 | pages=149–161 | date=July 2012 | doi=10.1016/j.icarus.2012.04.026 | arxiv=1112.5363 | bibcode=2012Icar..220..149F }}</ref> Some, such as [[90 Antiope]], are double asteroids with two comparably sized components.<ref>{{cite journal | title=A giant crater on 90 Antiope? | last1=Descamps | first1=P. | last2=Marchis | first2=F. | last3=Michalowski | first3=T. | last4=Berthier | first4=J. | last5=Pollock | first5=J. | last6=Wiggins | first6=P. | last7=Birlan | first7=M. | last8=Colas | first8=F. | last9=Vachier | first9=F. | last10=Fauvaud | first10=S. | last11=Fauvaud | first11=M. | last12=Sareyan | first12=J. -P. | last13=Pilcher | first13=F. | last14=Klinglesmith | first14=D. A. | journal=Icarus | volume=203 | issue=1 | pages=102–111 | date=September 2009 | doi=10.1016/j.icarus.2009.04.022 | arxiv=0905.0631 | bibcode=2009Icar..203..102D }}</ref> For astronomers, a useful aspect of an asteroid satellite is that it can be used to determine the density of the primary asteroid, without the need for a spacecraft fly-by mission.<ref>{{cite book | chapter=Asteroids Do Have Satellites | last1=Merline | first1=W. J. | last2=Weidenschilling | first2=S. J. | last3=Durda | first3=D. D. | last4=Margot | first4=J. L. | last5=Pravec | first5=P. | last6=Storrs | first6=A. D. | title=Asteroids III | editor1-first=W. F. | editor1-last=Bottke Jr. | editor2-first=A. | editor2-last=Cellino | editor3-first=P. | editor3-last=Paolicchi | editor4-first=R. P. | editor4-last=Binzel | publisher=University of Arizona Press | location=Tucson | pages=289–312 | date=March 2002 | bibcode=2002aste.book..289M | chapter-url=https://books.google.com/books?id=X9W64CkTUD&pg=PA289 }}</ref>

Besides planets and dwarf planets objects within the Solar System known to have natural satellites are 76 in the [[asteroid belt]] (five with two each), four [[Jupiter trojan]]s, 39 [[near-Earth object]]s (two with two satellites each), and 14 [[List of Mars-crossing minor planets|Mars-crossers]].<ref name="Johnston" /> There are also 84 known natural satellites of [[trans-Neptunian objects]].<ref name="Johnston" /> Some 150 additional small bodies have been observed within the [[rings of Saturn]], but only a few were tracked long enough to establish orbits.

===Dimensions===
The seven largest [[List of natural satellites|natural satellites]] in the Solar System (those bigger than 2,500&nbsp;km across) are Jupiter's [[Galilean moon]]s (Ganymede, [[Callisto (moon)|Callisto]], Io, and [[Europa (moon)|Europa]]), Saturn's moon Titan, Earth's moon, and Neptune's captured natural satellite Triton.<ref name=Burns_Matthews_1986>{{cite book | chapter=Origins of Satellites | first1=D. J. | last1=Stevenson | first2=A. W. | last2=Harris | first3=J. I. | last3=Lunine | title=Satellites | editor1-first=Joseph A. | editor1-last=Burns | editor2-first=Mildred Shapley  | editor2-last=Matthews | publisher=University of Arizona Press | year=1986 | isbn=978-0-8165-4655-8 | pages=40–41 | chapter-url=https://books.google.com/books?id=Mdg7EAAAQBAJ&pg=PA40 }}</ref> Of these, Ganymede and Titan are larger than the planet Mercury, while Callisto is about the same size.<ref name=Koupelis_2010>{{cite book | title=In Quest of the Universe | series=Jones and Bartlett Titles in Physical Science | first=Theo | last=Koupelis | publisher=Jones & Bartlett Learning | year=2010 | isbn=978-0-7637-6858-4 | page=213 | url=https://books.google.com/books?id=GVlpKZ67DscC&pg=PA213 }}</ref> The next size group of nine mid-sized natural satellites, between 1,000&nbsp;km and 1,600&nbsp;km across, consists of [[Titania (moon)|Titania]], [[Oberon (moon)|Oberon]], [[Rhea (moon)|Rhea]], [[Iapetus (moon)|Iapetus]], Charon, [[Ariel (moon)|Ariel]], [[Umbriel]], [[Dione (moon)|Dione]], and Tethys, the smallest.<ref name=Hussman_et_al_2010>{{cite book | chapter=Interiors and Evolution of Icy Satellites | first1=H. | last1=Hussman | first2=C. | last2=Sotin | first3=J. I. | last3=Lunine | title=Planets and Moons | volume=10 | series=Treatise on Geophysics | editor-first=Tilman | editor-last=Spohn | publisher=Newnes | year=2010 | isbn=978-0-444-53574-0 | pages=510–512 | chapter-url=https://books.google.com/books?id=xqxFMGC1gucC&pg=PA511 }}</ref> As well as the natural satellites of the various planets, there are hundreds of known natural satellites of the [[dwarf planet]]s, [[minor planet]]s and other [[small Solar System body|small Solar System bodies]].<ref name="Johnston"/>

A planet usually has at least around 10,000 times the mass of any natural satellites that orbit it, with a correspondingly much larger diameter.<ref name="2006Natur.441..834C"/>{{Verify source|date=August 2025|reason=Per the abstract, the article claim primarily addreses only the giant planets, and uses a rough order of magnitude estimate that seems misinterpreted here. Of 4 giant planets, Saturn and Neptune are cited below as exceptions to this "rule."}} The [[Earth–Moon system]] is a unique exception in the Solar System; at 3,474&nbsp;kilometres (2,158 miles) across, the Moon is 0.273 times the [[diameter]] of Earth and about {{frac|80}} of its mass.<ref name="GuinnessWR2014"/> The next largest ratios are the [[Neptune]]–[[Triton (moon)|Triton]] system at 0.055 (with a mass ratio of about 1 to 4790), the [[Saturn]]–[[Titan (moon)|Titan]] system at 0.044 (with the second mass ratio next to the Earth–Moon system, 1 to 4225), the [[Jupiter]]–[[Ganymede (moon)|Ganymede]] system at 0.038 (with a mass ratio of 12810), and the [[Uranus]]–[[Titania (moon)|Titania]] system at 0.031 (with a mass ratio of 25125). For the category of [[dwarf planet]]s, [[Charon (moon)|Charon]] has the largest ratio, being 0.52 the diameter and 12.2% the mass of [[Pluto]].

The following is a comparative table classifying the natural satellites in the Solar System by diameter. The column on the right includes some notable planets, dwarf planets, asteroids, and trans-Neptunian objects for comparison. The natural satellites of the planets are named after mythological figures. These are predominantly Greek, except for the [[moons of Uranus|Uranian natural satellites]], which are named after Shakespearean characters. The twenty satellites massive enough to be round are in bold in the table below. Minor planets and satellites where there is disagreement in the literature on roundness are italicized in the table below.

{| class="wikitable" style="text-align:center; font-size:90%; clear: right;"
|-
! rowspan="2" style="vertical-align:bottom; width:8%;" | Mean<br />diameter<br />(km)
! colspan="6" style="background:#cae1ff; text-align:center;" | Satellites of planets
! colspan="7" style="background:#ffdead; text-align:center;" | Satellites of dwarf planets
! rowspan="2" style="width:8%; background:#b2e5cd;" | Satellites of<br />other<br />[[minor planet]]s
! rowspan="2" style="width:8%; background:#7ec0ee;" | Non-satellites<br />for comparison
|-
! style="width:9%; background:#cae1ff;" | Earth
! style="width:9%; background:#cae1ff;" | Mars
! style="width:9%; background:#cae1ff;" | Jupiter
! style="width:9%; background:#cae1ff;" | Saturn
! style="width:9%; background:#cae1ff;" | Uranus
! style="width:9%; background:#cae1ff;" | Neptune
! style="width:6.5%; background:#ffdead;" | Orcus
! style="width:6.5%; background:#ffdead;" | Pluto
! style="width:6.5%; background:#ffdead;" | Haumea
! style="width:6.5%; background:#ffdead;" | Quaoar
! style="width:6.5%; background:#ffdead;" | Makemake
! style="width:6.5%; background:#ffdead;" | Gonggong
! style="width:6.5%; background:#ffdead;" | Eris
|-
! 4,000–6,000
|<!--Earth-->
|<!--Mars-->
| <!--Jupiter-->'''[[Ganymede (moon)|Ganymede]]'''<br />'''[[Callisto (moon)|Callisto]]'''
| <!--Saturn-->'''[[Titan (moon)|Titan]]'''
|<!--Uranus-->
|<!--Neptune-->
|<!--Orcus-->
|<!--Pluto-->
|<!--Haumea-->
|<!--Quaoar-->
|<!--Makemake-->
|<!--Gonggong-->
|<!--Eris-->
|<!--Minor planets-->
| <!--Other objects-->'''[[Mercury (planet)|Mercury]]'''
|-
! 3,000–4,000
| <!--Earth-->'''[[Moon]]'''
|<!--Mars-->
| <!--Jupiter-->'''[[Io (moon)|Io]]<br />[[Europa (moon)|Europa]]'''
|<!--Saturn-->
|<!--Uranus-->
|<!--Neptune-->
|<!--Orcus-->
|<!--Pluto-->
|<!--Haumea-->
|<!--Quaoar-->
|<!--Makemake-->
|<!--Gonggong-->
|<!--Eris-->
|<!--Minor planets-->
|<!--Other objects-->
|-
! 2,000–3,000
|<!--Earth-->
|<!--Mars-->
|<!--Jupiter-->
|<!--Saturn-->
|<!--Uranus-->
| <!--Neptune-->'''[[Triton (moon)|Triton]]'''
|<!--Orcus-->
|<!--Pluto-->
|<!--Haumea-->
|<!--Quaoar-->
|<!--Makemake-->
|<!--Gonggong-->
|<!--Eris-->
|<!--Minor planets-->
| <!--Other objects-->'''{{dp|Eris}}'''<br />'''[[Pluto]]'''
|-
! 1,000–2,000
|<!--Earth-->
|<!--Mars-->
|<!--Jupiter-->
| <!--Saturn-->'''[[Rhea (moon)|Rhea]]<br />[[Iapetus (moon)|Iapetus]]<br />[[Dione (moon)|Dione]]<br />[[Tethys (moon)|Tethys]]'''
| <!--Uranus-->'''[[Titania (moon)|Titania]]<br />[[Oberon (moon)|Oberon]]<br />[[Umbriel]]<br />[[Ariel (moon)|Ariel]]'''
|<!--Neptune-->
|<!--Orcus-->
| <!--Pluto-->'''[[Charon (moon)|Charon]]'''
|<!--Haumea-->
|<!--Quaoar-->
|<!--Makemake-->
|<!--Gonggong-->
|<!--Eris-->
|<!--Minor planets-->
| <!--Other objects-->'''{{dp|Makemake}}'''<br />'''[[Haumea]]'''<br />'''[[225088 Gonggong|Gonggong]]''',<br />'''[[50000 Quaoar|Quaoar]]'''
|-
! 500–1,000
|<!--Earth-->
|<!--Mars-->
|<!--Jupiter-->
| <!--Saturn-->'''[[Enceladus]]'''
|<!--Uranus-->
|<!--Neptune-->
|<!--Orcus-->
|<!--Pluto-->
|<!--Haumea-->
|<!--Quaoar-->
|<!--Makemake-->
|<!--Gonggong-->
| <!--Eris-->''[[Dysnomia (moon)|Dysnomia]]''
|<!--Minor planets-->
|<!--Other objects-->'''[[90377 Sedna|Sedna]]''', '''[[Ceres (dwarf planet)|Ceres]]''',<br />''[[120347 Salacia|Salacia]]'', ''[[90482 Orcus|Orcus]]'',<br />''[[2 Pallas|Pallas]]'', ''[[4 Vesta|Vesta]]''<br />{{small|many more [[Trans-Neptunian Object|TNOs]]}}
|-
! 250–500
|<!--Earth-->
|<!--Mars-->
|<!--Jupiter-->
| <!--Saturn-->'''[[Mimas (moon)|Mimas]]'''<br />[[Hyperion (moon)|Hyperion]]
| <!--Uranus-->'''[[Miranda (moon)|Miranda]]'''
| <!--Neptune-->[[Proteus (moon)|Proteus]]<br />[[Nereid (moon)|Nereid]]
|<!--Orcus-->[[Vanth (moon)|Vanth]]
|<!--Pluto-->
| <!--Haumea-->[[Hiʻiaka (moon)|Hiʻiaka]]
|<!--Quaoar-->
|<!--Makemake-->
|<!--Gonggong-->
|<!--Eris-->
|<!--Minor planets-->[[Actaea (moon)|Salacia I Actaea]]<br/>[[Ilmarë (moon)|Varda I Ilmarë]]<br />[[Hiisi (moon)|Lempo&nbsp;II&nbsp;Hiisi]]
|<!--Other objects-->''[[10 Hygiea]]''<br />{{nowrap|''[[704 Interamnia]]''}}<br />[[87 Sylvia]]<br />[[47171 Lempo]]
[[107 Camilla]]<br />{{small|and [[Largest asteroids|many]] [[List of dwarf planet candidates|others]]}}
|-
! 100–250
|<!--Earth-->
|<!--Mars-->
| <!--Jupiter-->[[Amalthea (moon)|Amalthea]]<br />[[Himalia (moon)|Himalia]]<br />[[Thebe (moon)|Thebe]]
| <!--Saturn-->[[Phoebe (moon)|Phoebe]]<br />[[Janus (moon)|Janus]]<br />[[Epimetheus (moon)|Epimetheus]]
| <!--Uranus-->[[Sycorax (moon)|Sycorax]]<br />[[Puck (moon)|Puck]]<br />[[Portia (moon)|Portia]]
| <!--Neptune-->[[Larissa (moon)|Larissa]]<br />[[Galatea (moon)|Galatea]]<br />[[Despina (moon)|Despina]]
|<!--Orcus-->
|<!--Pluto-->
| <!--Haumea-->[[Namaka (moon)|Namaka]]
|<!--Quaoar-->
| <!--Makemake-->[[S/2015 (136472) 1]]
|<!--Gonggong-->
|<!--Eris-->
| <!--Minor planets-->[[(82075) 2000 YW134|S/2005&nbsp;(82075)]]&nbsp;1<br />[[79360 Sila–Nunam|Sila–Nunam]]&nbsp;I<br />[[65489 Ceto|Ceto]]&nbsp;I Phorcys<br />[[617 Patroclus|Patroclus]]&nbsp;I&nbsp;Menoetius<br />[[Paha (moon)|Lempo&nbsp;I&nbsp;Paha]]<br />{{small|~20 more [[Minor planet moon#Trans-Neptunian objects|moons of]] [[Trans-Neptunian Object|TNOs]]}}
| <!--Other objects-->[[3 Juno]]<br />[[15760 Albion]]<br />[[5 Astraea]]<br />[[617 Patroclus]]<br />[[42355 Typhon]]<br />{{small|and many others}}
|-
! 50–100
|<!--Earth-->
|<!--Mars-->
| <!--Jupiter-->[[Elara (moon)|Elara]]<br />[[Pasiphae (moon)|Pasiphae]]
| <!--Saturn-->[[Prometheus (moon)|Prometheus]]<br />[[Pandora (moon)|Pandora]]
| <!--Uranus-->[[Caliban (moon)|Caliban]]<br />[[Juliet (moon)|Juliet]]<br />[[Belinda (moon)|Belinda]]<br />[[Cressida (moon)|Cressida]]<br />[[Rosalind (moon)|Rosalind]]<br />[[Desdemona (moon)|Desdemona]]<br />[[Bianca (moon)|Bianca]]
| <!--Neptune-->[[Thalassa (moon)|Thalassa]]<br />[[Halimede (moon)|Halimede]]<br />[[Neso (moon)|Neso]]<br />[[Naiad (moon)|Naiad]]
|<!--Orcus-->
|<!--Pluto-->
|<!--Haumea-->
| <!--Quaoar-->[[Weywot]]
|<!--Makemake-->
| <!--Gonggong-->[[Xiangliu (moon)|Xiangliu]] (probably)
|<!--Eris-->
| <!--Minor planets-->[[90 Antiope]]&nbsp;I<br />[[42355 Typhon|Typhon]]&nbsp;I&nbsp;Echidna<br />[[58534 Logos|Logos]]&nbsp;I&nbsp;Zoe<br />{{small|5 more [[Minor planet moon#Trans-Neptunian objects|moons of TNOs]]}}<!--- No TNO moons below Zoe's size (66 km) are known--->
| <!--Other objects-->[[90 Antiope]]<br />[[58534 Logos]]<br />[[253 Mathilde]]<br />{{small|and many others}}
|-
! 25–50
|<!--Earth-->
|<!--Mars-->
| <!--Jupiter-->[[Carme (moon)|Carme]]<br />[[Metis (moon)|Metis]]<br />[[Sinope (moon)|Sinope]]<br />[[Lysithea (moon)|Lysithea]]<br />[[Ananke (moon)|Ananke]]
| <!--Saturn-->[[Siarnaq (moon)|Siarnaq]]<br />[[Helene (moon)|Helene]]<br />[[Albiorix (moon)|Albiorix]]<br />[[Atlas (moon)|Atlas]]<br />[[Pan (moon)|Pan]]
| <!--Uranus-->[[Ophelia (moon)|Ophelia]]<br />[[Cordelia (moon)|Cordelia]]<br />[[Setebos (moon)|Setebos]]<br />[[Prospero (moon)|Prospero]]<br />[[Perdita (moon)|Perdita]]<br />[[Stephano (moon)|Stephano]]
| <!--Neptune-->[[Sao (moon)|Sao]]<br />[[S/2002 N 5]]<br />[[Laomedeia (moon)|Laomedeia]]<br />[[Psamathe (moon)|Psamathe]]<br />[[Hippocamp (moon)|Hippocamp]]
|<!--Orcus-->
| <!--Pluto-->[[Hydra (moon)|Hydra]]<br />[[Nix (moon)|Nix]]<ref>{{cite web|url=http://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|work=NASA|date=13 July 2015|access-date=16 July 2015|archive-date=1 July 2017|archive-url=https://web.archive.org/web/20170701005734/https://www.nasa.gov/feature/how-big-is-pluto-new-horizons-settles-decades-long-debate/|url-status=dead}}</ref>
|<!--Haumea-->
|<!--Quaoar-->
|<!--Makemake-->
|<!--Gonggong-->
|<!--Eris-->
| <!--Minor planets-->{{nowrap|[[Linus (moon)|Kalliope I Linus]]}}
| <!--Other objects-->[[1036 Ganymed]]<br />[[243 Ida]]<br />{{small|and many others}}
|-
! 10–25
|<!--Earth-->
| <!--Mars-->[[Phobos (moon)|Phobos]]<br />[[Deimos (moon)|Deimos]]
| <!--Jupiter-->[[Leda (moon)|Leda]]<br />[[Adrastea (moon)|Adrastea]]
| <!--Saturn-->[[Telesto (moon)|Telesto]]<br />[[Paaliaq (moon)|Paaliaq]]<br />[[Calypso (moon)|Calypso]]<br />[[Ymir (moon)|Ymir]]<br />[[Kiviuq (moon)|Kiviuq]]<br />[[Tarvos (moon)|Tarvos]]<br />[[Ijiraq (moon)|Ijiraq]]<br />[[Erriapus]]
| <!--Uranus-->[[Mab (moon)|Mab]]<br />[[Cupid (moon)|Cupid]]<br />[[Francisco (moon)|Francisco]]<br />[[Ferdinand (moon)|Ferdinand]]<br />[[Margaret (moon)|Margaret]]<br />[[Trinculo (moon)|Trinculo]]<br />[[S/2023 U 1]]
|<!--Neptune-->[[S/2021 N 1]] (?)
|<!--Orcus-->
| <!--Pluto-->[[Kerberos (moon)|Kerberos]]<br />[[Styx (moon)|Styx]]
|<!--Haumea-->
|<!--Quaoar-->
|<!--Makemake-->
|<!--Gonggong-->
|<!--Eris-->
| <!--Minor planets-->[[762 Pulcova]] I<br />{{nowrap|[[Romulus (moon)|Sylvia I Romulus]]}}<br />[[624 Hektor]]&nbsp;I&nbsp;Skamandrios<br />{{nowrap|[[Petit-Prince (moon)|Eugenia I Petit-Prince]]}}<br />[[121 Hermione]]&nbsp;I<br />[[283 Emma]]&nbsp;I<br />[[1313 Berna]]&nbsp;I<br />[[107 Camilla]] I
| <!--Other objects-->[[433 Eros]]<br />[[1313 Berna]]<br />{{small|and many others}}
|-
! < 10
|<!--Earth-->
|<!--Mars-->
| <!--Jupiter-->[[Moons of Jupiter|''81 moons'']]<!--THESE ARE THE NUMBER OF MOONS SMALLER THAN 10 KM, NOT THE TOTAL NUMBER!-->
| <!--Saturn-->[[Moons of Saturn|''248 moons'']]<!--THESE ARE THE NUMBER OF MOONS SMALLER THAN 10 KM, NOT THE TOTAL NUMBER!-->
|<!--Uranus-->[[S/2025 U 1]] (?)
|<!--Neptune-->
|<!--Orcus-->
|<!--Pluto-->
|<!--Haumea-->
|<!--Quaoar-->
|<!--Makemake-->
|<!--Gonggong-->
|<!--Eris-->
| <!--Minor planets-->{{nowrap|[[Remus (moon)|Sylvia II Remus]]}}<br />{{nowrap|[[Dactyl (asteroid)|Ida I Dactyl]]}}<br />{{small|[[List of asteroid moons#List of minor planets with moons|and many others]]}}
| <!--Other objects-->many
|}

==See also==
{{cmn|colwidth=30em|
* {{annotated link|Circumplanetary disk}}
* {{annotated link|Co-orbital moon}}
* {{annotated link|Exomoon}}
* {{annotated link|Inner moon}}
* {{annotated link|Irregular moon}}
* {{annotated link|Regular moon}}
* [[List of natural satellites]]
* {{annotated link|Naming of moons}}
* {{annotated link|Planetary-mass moon}}
* {{annotated link|Quasi-satellite}}
* {{annotated link|Subsatellite}} (aka Submoon)
* [[Timeline of discovery of Solar System planets and their moons]]
* {{annotated link|Trojan moon}}
* {{annotated link|Tug of war (astronomy)}}
}}

=== Moons of planets ===
{{cmn|colwidth=30em|
* The [[Moon]], Earth's natural satellite
* [[Moons of Mars]]
* [[Moons of Jupiter]]
* [[Moons of Saturn]]
* [[Moons of Uranus]]
* [[Moons of Neptune]]
}}

===Moons of dwarf planets and small Solar System bodies===
{{cmn|colwidth=30em|
* [[Minor-planet moon]]
* [[Moons of Pluto]]
* [[Dysnomia (moon)|Dysnomia]], Eris's natural satellite
* [[Moons of Haumea]]
* [[S/2015 (136472) 1]], Makemake's natural satellite
* [[Xiangliu (moon)|Xiangliu]], Gonggong's natural satellite
* [[Weywot]], Quaoar's natural satellite
* [[Vanth (moon)|Vanth]], Orcus' natural satellite
}}

==References==
<references>
<ref name="WGPSN">{{cite web
  |title=Planet and Satellite Names and Discoverers
  |publisher=International Astronomical Union (IAU) Working Group for Planetary System Nomenclature (WGPSN)
  |url=http://planetarynames.wr.usgs.gov/Page/Planets#DwarfPlanets
  |access-date=27 January 2012}}</ref>

<ref name="Johnston">{{cite web
 | date=30 September 2018
 | title=Asteroids with Satellites
 | publisher=Johnston's Archive
 | first=Wm. Robert | last=Johnston
 | url=http://www.johnstonsarchive.net/astro/asteroidmoons.html
 | access-date=22 October 2018}}</ref>

<ref name="2006Natur.441..834C">
{{Cite journal
 |last1=Canup |first1=Robin M.
 |author1-link=Robin Canup
 |last2=Ward |first2=William R.
 |title=A common mass scaling for satellite systems of gaseous planets
 |url=https://www.nature.com/articles/nature04860
 |journal=Nature
 |language=en
 |volume=441|issue=7095|pages=834–839
 |date=June 2006
 |bibcode=2006Natur.441..834C
 |doi=10.1038/nature04860
 |issn=1476-4687
 |pmid=16778883
 |s2cid=4327454
|url-access=subscription
 }}</ref>

<ref name="NASA-what-is-a-satellite">
{{cite web|last1=Stillman|first1=Dan|title=What Is a Satellite?
|url=http://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-a-satellite-58.html
|website=www.nasa.gov|publisher=NASA|access-date=16 November 2015|date=16 June 2015}}
</ref>

<ref name="NASA-firstsatellites">{{Cite web|url=https://www.jpl.nasa.gov/jplhistory/early/firstsatellites.php|title=Early History – First Satellites|website=www.jpl.nasa.gov|access-date=2018-02-08|archive-date=7 February 2018|archive-url=https://web.archive.org/web/20180207135844/https://www.jpl.nasa.gov/jplhistory/early/firstsatellites.php|url-status=dead}}</ref>

<ref name="NASA2015">{{Cite web|title = NASA's Hubble Finds Pluto's Moons Tumbling in Absolute Chaos|url = https://www.nasa.gov/press-release/nasa-s-hubble-finds-pluto-s-moons-tumbling-in-absolute-chaos|website = NASA|date = 3 June 2015|access-date = 25 October 2015|first = Karen|last = Northon}}</ref>

<ref name="GuinnessWR2014">
{{Cite book|title=Guinness World Records 2014|last=Glenday|first=Craig|year=2014|isbn=978-1-908843-15-9|page=[https://archive.org/details/guinnessworldrec0000unse_r3e7/page/186 186]|publisher=Guinness World Records Limited |url=https://archive.org/details/guinnessworldrec0000unse_r3e7/page/186}}</ref>
</references> <!-- end of reflist -->

==External links==
{{Commons category|Moons}}

===All moons===
* [http://ssd.jpl.nasa.gov/?sat_phys_par Natural Satellite Physical Parameters] (JPL-NASA, with refs – last updated July 2006)
* [https://web.archive.org/web/20070227165513/http://www.planetary.org/explore/topics/compare_the_planets/moon_numbers.html Moons of the Solar System] (The Planetary Society, as of March 2009)
* [http://ssd.jpl.nasa.gov/ The JPL's Solar System Dynamics page]
* {{cite web |title=How Many Solar System Bodies |publisher=NASA/JPL Solar System Dynamics |url=http://ssd.jpl.nasa.gov/?body_count |access-date=26 January 2012}}
* [https://planetarynames.wr.usgs.gov/Page/Planets Planetary Names: Planet and Satellite Names and Discoverers]
* [https://www.newscientist.com/article/dn9336-upper-size-limit-for-moons-explained/ "Upper size limit for moons explained"] Kelly Young. ''Nature'' (vol 441, p.&nbsp;834) 14 June 2006
* [http://www.hudsonfla.com/spaceplanets.htm Images of planets and major moons (not to scale)]
* [http://www.planetary.org/blogs/emily-lakdawalla/2013/scale-comparisons-solar-system-moons.html The Planetary Society – Moon Montage(s)]
* [https://www.flickr.com/photos/kevinmgill/albums/72157664303348108 Album] of moon images by Kevin M. Gill
* [https://web.archive.org/web/20190709182950/https://www.nationalgeographic.com/science/2019/07/the-atlas-of-moons/ The Atlas of Moons] by the National Geographic Society

===Jupiter's moons===
* {{cite web|url=http://home.dtm.ciw.edu/users/sheppard/satellites/|title=The Jupiter Satellite and Moon Page|author=Sheppard, Scott S.|publisher=Department of Terrestrial Magnetism at Carnegie Institution for Science|access-date=8 March 2018|archive-date=31 May 2018|archive-url=https://web.archive.org/web/20180531184410/http://home.dtm.ciw.edu/users/sheppard/satellites/jup2003.html|url-status=dead}}* Scott S. Sheppard
* Scott S. Sheppard

===Saturn's moons===
* [https://news.cornell.edu/stories/2000/10/satellite-hunting-team-finds-four-new-moons-saturn Satellite-hunters find four new moons of the planet Saturn] David Brand | 26 October 2000
* [https://web.archive.org/web/20180531022057/http://home.dtm.ciw.edu/users/sheppard/satellites/sat2003.html Saturn's New Satellite S/2003 S1] Scott S. Sheppard

{{Solar System moons}}
{{Small Solar System bodies}}
{{Solar System}}
{{Portal bar|Astronomy|Spaceflight|Outer space|Solar System}}
{{Authority control}}

{{DEFAULTSORT:Natural Satellite}}
[[Category:Moons| ]]
[[Category:Solar System]]