View source for Astronomy:Natural satellite

{{short description|Astronomical body that orbits a planet}}
[[File:Dscovrepicmoontransitfull-startinmiddle.gif|thumb|upright=1.35|Earth and the Moon orbiting around Earth (observed by the Deep Space Climate Observatory)]]

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

In the [[Astronomy:Solar System|Solar System]], there are six planetary [[Astronomy:Satellite system|satellite systems]] containing 284 known natural satellites altogether. Seven objects commonly considered [[Astronomy:Dwarf planet|dwarf planet]]s by astronomers are also known to have natural satellites: {{dp|Orcus}}, [[Astronomy:Moons of Pluto|Pluto]], [[Astronomy:Moons of Haumea|Haumea]], {{dp|Quaoar}}, [[Astronomy:Makemake|Makemake]], {{dp|Gonggong}}, and [[Astronomy:Eris (dwarf planet)|Eris]].<ref name="WGPSN"/> {{As of|2021|11}}, there are 442 other [[Astronomy:Minor-planet moon|minor planets known to have natural satellites]].<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>{{Cite journal|last1=Canup|first1=Robin M.|last2=Ward|first2=William R.|date=June 2006|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|doi=10.1038/nature04860|pmid=16778883|bibcode=2006Natur.441..834C|s2cid=4327454|issn=1476-4687}}</ref> 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|diameter]] of Earth and about {{frac|80}} of its mass.<ref>{{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> The next largest ratios are the [[Astronomy:Neptune|Neptune]]–[[Astronomy:Triton (moon)|Triton]] system at 0.055 (with a mass ratio of about 1 to 4790), the [[Astronomy:Saturn|Saturn]]–[[Astronomy:Titan (moon)|Titan]] system at 0.044 (with the second mass ratio next to the Earth–Moon system, 1 to 4220), the [[Astronomy:Jupiter|Jupiter]]–[[Astronomy:Ganymede (moon)|Ganymede]] system at 0.038, and the [[Astronomy:Uranus|Uranus]]–[[Astronomy:Titania (moon)|Titania]] system at 0.031.  For the category of [[Astronomy:Dwarf planet|dwarf planet]]s, [[Astronomy:Charon (moon)|Charon]] has the largest ratio, being 0.52 the diameter and 12.2% the mass of [[Astronomy:Pluto|Pluto]].

==Terminology==
The first known natural satellite was the [[Astronomy:Moon|Moon]], but it was considered a "planet" until [[Biography:Nicolaus Copernicus|Copernicus]]' introduction of ''[[Astronomy:De revolutionibus orbium coelestium|De revolutionibus orbium coelestium]]'' in 1543. Until the discovery of the [[Astronomy:Galilean moons|Galilean satellites]] in 1610 there was no opportunity for referring to such objects as a class. [[Biography: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.{{citation needed|date=November 2016}}

The first to use the term ''satellite'' to describe orbiting bodies was the German astronomer [[Biography:Johannes Kepler|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 [[Social:Latin|Latin]] word ''satelles'', meaning "guard", "attendant", or "companion", because the ''satellites'' accompanied their primary planet in their journey through the heavens.<ref name=autogenerated1>{{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>

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 [[Engineering:Sputnik|Sputnik]] created a need for new terminology.<ref name=autogenerated1 /> The terms ''man-made satellite'' and ''artificial moon'' were very quickly abandoned in favor of the simpler ''satellite'', and as a consequence, the term has become linked primarily with artificial objects flown in space.{{citation needed|date=January 2017}}

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 in 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 nouns).

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>Kenneth R. Lang.
[https://books.google.com/books?id=S4xDhVCxAQIC "The Cambridge Guide to the Solar System"] {{Webarchive|url=https://web.archive.org/web/20230104160756/https://books.google.com/books?id=S4xDhVCxAQIC |date=4 January 2023 }}.
2011.
p. 15.
quote: "Any object that orbits a planet is now called a satellite, and a natural satellite is also now called a moon."</ref><ref>
[[Biography:Thérèse Encrenaz|Thérèse Encrenaz]], et al.
[https://books.google.com/books?id=Je61Y7UbqWgC "The Solar System"].
2004.
p. 30.
</ref><ref>Tilman Spohn, Doris Breuer, Torrence Johnson.
[https://books.google.com/books?id=0bEMAwAAQBAJ "Encyclopedia of the Solar System"] {{Webarchive|url=https://web.archive.org/web/20230104160757/https://books.google.com/books?id=0bEMAwAAQBAJ |date=4 January 2023 }}.
2014.
p. 18.</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>
David Andrew Weintraub.
[https://books.google.com/books?id=ELd-ve_35R8C "Is Pluto a Planet?: A Historical Journey Through the Solar System"].
p. 65
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>
{{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>

=== 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 [[Astronomy:Solar System|Solar System]], some as small as a kilometer across, has been considered a moon, though objects a tenth that size within Saturn's rings, which have not been directly observed, have been called ''[[Astronomy:Moonlet|moonlet]]s''. Small [[Astronomy:Minor-planet moon|asteroid moons]] (natural satellites of asteroids), such as [[Astronomy:Dactyl (moon)|Dactyl]], have also been called moonlets.<ref name="Marchis05">{{cite journal|author=F. Marchis|title=Discovery of the triple asteroidal system 87 Sylvia|journal=Nature|volume=436|pages=822–824|date=2005|bibcode=2005Natur.436..822M|doi=10.1038/nature04018|pmid=16094362|issue=7052|name-list-style=vanc|display-authors=1|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 [[Astronomy:Double planet|double planet]] rather than primary and satellite. [[Astronomy:Asteroid|Asteroid]]s such as [[Astronomy:90 Antiope|90 Antiope]] are considered double asteroids, 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. The most common{{citation needed|date=January 2012}} dividing line on what is considered a moon rests upon whether the barycentre is below the surface of the larger body, though this is somewhat arbitrary, because it depends on distance as well as relative mass.

== Origin and orbital characteristics ==
{{further|Astronomy:Circumplanetary disk}}
The natural satellites orbiting relatively close to the planet on [[Astronomy:Retrograde and prograde motion|prograde]], uninclined circular orbits ([[Astronomy:Regular moon|''regular'' satellites]]) are generally thought to have been formed out of the same [[Astronomy:Circumplanetary disk|collapsing region]] of the [[Astronomy:Protoplanetary disk|protoplanetary disk]] that created its primary.<ref name="arxiv0812">{{cite book |author1=Canup, Robin M. |author2=Ward, 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 satellites (generally orbiting on distant, [[Astronomy:Orbital inclination|inclined]], [[Astronomy:Orbital eccentricity|eccentric]] and/or retrograde orbits) are thought to be captured [[Astronomy:Asteroid|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>Encyclopedia of the Solar System, page 366, Academic Press, 2007, Lucy-Ann Adams McFadden, Paul Robert Weissman, Torrence V. Johnson</ref> The [[Astronomy:Moon|Moon]] and the [[Astronomy:Moons of Pluto|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 = RM | last2 = Asphaug | first2 = E | name-list-style=amp | 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 = SA | display-authors = 4 | last2 = Weaver | first2 = HA | last3 = Steffl | first3 = AJ | last4 = Mutchler | first4 = MJ | last5 = Merline | first5 = WJ | last6 = Buie | first6 = MW | last7 = Young | first7 = EF | last8 = Young | first8 = LA | last9 = Spencer | first9 = JR | 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 moons are thought to commonly form by this process. [[Astronomy: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 [[Astronomy:Dwarf planet|dwarf planet]].

=== Temporary satellites ===
{{Main|Astronomy:Temporary satellite}}
The capture of an asteroid from a heliocentric orbit is not always permanent. According to simulations, [[Astronomy:Temporary satellite|temporary satellite]]s should be a common phenomenon.<ref name="Carlisle">{{cite news |author=Camille M. 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> The only observed examples are {{mpl|1991 VG}}, {{mpl|2006 RH|120}}, {{mpl|2020 CD|3}}.

{{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 |author=Roger W. 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|Astronomy:Tidal locking}}

Most [[Astronomy:Regular moon|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=978-3527408962 | page=248 | url=https://books.google.com/books?id=-7KimFtJnIAC&pg=PA248 }}</ref> Exceptions are known; one such exception is [[Astronomy:Saturn|Saturn]]'s natural satellite [[Astronomy:Hyperion (moon)|Hyperion]], which rotates chaotically because of the gravitational influence of [[Astronomy:Titan (moon)|Titan]]. 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 [[Astronomy:Himalia (moon)|Himalia]], Saturn's [[Astronomy:Phoebe (moon)|Phoebe]], and Neptune's [[Astronomy:Nereid (moon)|Nereid]] have rotation periods in the range of ten hours, whereas their orbital periods are hundreds of days.

== Satellites of satellites ==
{{Main|Astronomy:Subsatellite}}
[[File:Rhean rings PIA10246 Full res.jpg|thumb|Artist impression of 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.

However, 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 [[Astronomy:Rings of Rhea|ring system]] around Saturn's moon [[Astronomy: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
|author = Jeff Hecht
}}</ref> a phenomenon normally associated with [[Astronomy:Shepherd moon|shepherd moon]]s. However, targeted images taken by the ''[[Astronomy: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 had a satellite in the past; this is one of several hypotheses that have been put forward to account for its [[Astronomy:Equatorial ridge on Iapetus|equatorial ridge]].<ref>{{cite web|url=https://source.wustl.edu/2010/12/how-iapetus-saturns-outermost-moon-got-its-ridge/|title=How Iapetus, Saturn's outermost moon, got its ridge|date=13 December 2010}}</ref>

Light-curve analysis suggests that Saturn's irregular satellite [[Astronomy:Kiviuq (moon)|Kiviuq]] is extremely prolate, and is likely a [[Astronomy: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>

== Trojan satellites ==

Two natural satellites are known to have small companions at both their {{L4}} and {{L5}} [[Astronomy:Lagrangian point|Lagrangian point]]s, sixty degrees ahead and behind the body in its orbit. These companions are called trojan moons, as their orbits are analogous to the [[Astronomy:Trojan asteroid|trojan asteroid]]s of [[Astronomy:Jupiter|Jupiter]]. The trojan moons are [[Astronomy:Telesto (moon)|Telesto]] and [[Astronomy:Calypso (moon)|Calypso]], which are the leading and following companions, respectively, of the Saturnian moon Tethys; and [[Astronomy:Helene (moon)|Helene]] and [[Astronomy:Polydeuces (moon)|Polydeuces]], the leading and following companions of the Saturnian moon Dione.

== Asteroid satellites ==

The discovery of [[Astronomy:243 Ida|243 Ida]]'s natural satellite [[Astronomy:Dactyl (moon)|Dactyl]] in the early 1990s confirmed that some [[Astronomy:Asteroid|asteroid]]s have natural satellites; indeed, [[Astronomy:87 Sylvia|87 Sylvia]] has two. Some, such as [[Astronomy:90 Antiope|90 Antiope]], are double asteroids with two comparably sized components.

== Shape ==
<!--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, Enceladus, and 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 [[Astronomy:Proteus (moon)|Proteus]] is the largest irregularly shaped natural satellite; the shapes of Eris' moon [[Astronomy:Dysnomia (moon)|Dysnomia]] and Orcus' moon [[Astronomy:Vanth (moon)|Vanth]] are unknown. All other known natural satellites that are at least the size of Uranus's [[Astronomy:Miranda (moon)|Miranda]] have lapsed into rounded [[Ellipsoid|ellipsoid]]s under [[Astronomy:Hydrostatic equilibrium|hydrostatic equilibrium]], i.e. are "round/rounded satellites" and are sometimes categorized as [[Astronomy:Planetary-mass moon|planetary-mass moon]]s. (Dysnomia's density is known to be high enough that it is probably a solid ellipsoid as well.) 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. Saturn's moon Mimas, for example, has a major axis 9% greater than its polar axis and 5% greater than its other equatorial axis. [[Astronomy:Methone (moon)|Methone]], another of Saturn's moons, is only around 3&nbsp;km in diameter and [[:File:Methone PIA14633.jpg|visibly egg-shaped]]. The effect is smaller on the largest natural satellites, where their own 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.
{| 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<br />diameter}}
|-
| Mimas || [[Astronomy:Saturn|Saturn]] || 33.4 {{smaller|(20.4{{\}}13.0)}} || 8.4 {{smaller|(5.1{{\}}3.3)}}
|-
| [[Astronomy:Enceladus|Enceladus]] || Saturn || 16.6 || 3.3
|-
| [[Astronomy:Miranda (moon)|Miranda]] || [[Astronomy:Uranus|Uranus]] || 14.2 || 3.0
|-
| Tethys || Saturn || 25.8 || 2.4
|-
| [[Astronomy:Io (moon)|Io]] || [[Astronomy:Jupiter|Jupiter]] || 29.4 || 0.8
|-
| [[Astronomy:Moon|Luna]] || [[Astronomy:Earth|Earth]] || 4.3 || 0.1
|}

==Geological activity==
Of the twenty known natural satellites in the Solar System that are large enough to be gravitationally rounded, several remain geologically active today. [[Astronomy:Io (moon)|Io]] is the most volcanically active body in the Solar System, while [[Astronomy:Europa (moon)|Europa]], [[Astronomy:Enceladus|Enceladus]], [[Astronomy:Titan (moon)|Titan]] and [[Astronomy:Triton (moon)|Triton]] display evidence of ongoing [[Earth:Tectonics|tectonic activity]] and [[Astronomy:Cryovolcano|cryovolcanism]]. In the first three cases, the geological activity is powered by the [[Astronomy:Tidal heating#Tidal heating|tidal heating]] resulting from having [[Astronomy:Orbital eccentricity|eccentric orbits]] close to their giant-planet primaries. (This mechanism would have also operated on Triton in the past, before its orbit was [[Tidal circularization|circularized]].) Many other natural satellites, such as Earth's Moon, [[Astronomy:Ganymede (moon)|Ganymede]], Tethys and Miranda, show evidence of past geological activity, resulting from energy sources such as the [[Physics:Radioactive decay|decay]] of their [[Chemistry:Primordial nuclide|primordial]] [[Physics:Radionuclide|radioisotopes]], greater past orbital eccentricities (due in some cases to past orbital resonances), or the [[Astronomy:Planetary differentiation|differentiation]] or freezing of their interiors. 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 hydrocarbon lakes. Also Io and Callisto have atmospheres, even if 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 {{!}} The Planetary Society |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> Four of the largest natural satellites, Europa, Ganymede, [[Astronomy:Callisto (moon)|Callisto]], and Titan, are thought to have subsurface oceans of liquid water, while smaller Enceladus may have localized subsurface liquid water.

== 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.]]Besides planets and dwarf planets objects within our Solar System known to have natural satellites are 76 in the asteroid belt (five with two each), four Jupiter trojans, 39 near-Earth objects (two with two satellites each), and 14 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 [[Astronomy:Rings of Saturn|rings of Saturn]], but only a few were tracked long enough to establish orbits. Planets around other stars are likely to have satellites as well, and although numerous candidates have been detected to date, none have yet been confirmed.

Of the inner planets, [[Astronomy:Mercury (planet)|Mercury]] and [[Astronomy:Venus|Venus]] have no natural satellites; Earth has one large natural satellite, known as the Moon; and [[Astronomy:Mars|Mars]] has two tiny natural satellites, [[Astronomy:Phobos (moon)|Phobos]] and [[Astronomy:Deimos (moon)|Deimos]].
The [[Astronomy:Giant planet|giant planet]]s have extensive systems of natural satellites, including half a dozen comparable in size to Earth's Moon: the four Galilean moons, Saturn's Titan, and [[Astronomy:Neptune|Neptune]]'s Triton. Saturn has an additional six mid-sized natural satellites massive enough to have achieved [[Astronomy:Hydrostatic equilibrium|hydrostatic equilibrium]], and [[Astronomy:Uranus|Uranus]] has five. It has been suggested that some 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 |access-date=27 January 2015}}</ref>

Among the objects generally agreed by astronomers to be dwarf planets, [[Astronomy: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, Nix, Kerberos, and 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> [[Astronomy:Haumea|Haumea]] has two natural satellites; {{dp|Orcus}}, {{dp|Quaoar}}, [[Astronomy:Makemake|Makemake]], {{dp|Gonggong}}, and {{dp|Eris}} have one each. The Pluto–Charon system is unusual in that the [[Physics:Center of mass#Barycenter in astrophysics and astronomy|center of mass]] lies in open space between the two, a characteristic sometimes associated with a [[Astronomy:Double planet|double-planet]] system.

The seven largest [[Astronomy:List of natural satellites|natural satellites]] in the Solar System (those bigger than 2,500&nbsp;km across) are Jupiter's Galilean moons (Ganymede, [[Astronomy:Callisto (moon)|Callisto]], Io, and [[Astronomy:Europa (moon)|Europa]]), Saturn's moon Titan, Earth's moon, and Neptune's captured natural satellite Triton. Triton, the smallest of these, has more mass than all smaller natural satellites together. Similarly in the next size group of nine mid-sized natural satellites, between 1,000&nbsp;km and 1,600&nbsp;km across, [[Astronomy:Titania (moon)|Titania]], [[Astronomy:Oberon (moon)|Oberon]], [[Astronomy:Rhea (moon)|Rhea]], Iapetus, Charon, [[Astronomy:Ariel (moon)|Ariel]], [[Astronomy:Umbriel (moon)|Umbriel]], Dione, and Tethys, the smallest, Tethys, has more mass than all smaller natural satellites together. As well as the natural satellites of the various planets, there are also over 80 known natural satellites of the [[Astronomy:Dwarf planet|dwarf planet]]s, [[Astronomy:Minor planet|minor planet]]s and other [[Astronomy:Small Solar System body|small Solar System bodies]]. Some studies estimate that up to 15% of all trans-Neptunian objects could have satellites.

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 [[Astronomy: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="8" style="background:#ffdead; text-align:center;" | Satellites of dwarf planets
! rowspan="2" style="width:8%; background:#b2e5cd;" | Satellites of<br />other<br />[[Astronomy:Minor planet|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;" | Salacia
! 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-->'''[[Astronomy:Ganymede (moon)|Ganymede]]'''<br />'''[[Astronomy:Callisto (moon)|Callisto]]'''
| <!--Saturn-->'''[[Astronomy:Titan (moon)|Titan]]'''
|<!--Uranus-->
|<!--Neptune-->
|<!--Orcus-->
|<!--Pluto-->
|
|<!--Haumea-->
|<!--Quaoar-->
|<!--Makemake-->
|<!--Gonggong-->
|<!--Eris-->
|<!--Minor planets-->
| <!--Other objects-->'''[[Astronomy:Mercury (planet)|Mercury]]'''
|-
! 3,000–4,000
| <!--Earth-->'''[[Astronomy:Moon|Moon]]'''
|<!--Mars-->
| <!--Jupiter-->'''[[Astronomy:Io (moon)|Io]]<br />[[Astronomy: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-->'''[[Astronomy:Triton (moon)|Triton]]'''
|<!--Orcus-->
|<!--Pluto-->
|
|<!--Haumea-->
|<!--Quaoar-->
|<!--Makemake-->
|<!--Gonggong-->
|<!--Eris-->
|<!--Minor planets-->
| <!--Other objects-->'''{{dp|Eris}}'''<br />'''[[Astronomy:Pluto|Pluto]]'''
|-
! 1,000–2,000
|<!--Earth-->
|<!--Mars-->
|<!--Jupiter-->
| <!--Saturn-->'''[[Astronomy:Rhea (moon)|Rhea]]<br />Iapetus<br />Dione<br />Tethys'''
| <!--Uranus-->'''[[Astronomy:Titania (moon)|Titania]]<br />[[Astronomy:Oberon (moon)|Oberon]]<br />[[Astronomy:Umbriel (moon)|Umbriel]]<br />[[Astronomy:Ariel (moon)|Ariel]]'''
|<!--Neptune-->
|<!--Orcus-->
| <!--Pluto-->'''[[Astronomy:Charon (moon)|Charon]]'''
|
|<!--Haumea-->
|<!--Quaoar-->
|<!--Makemake-->
|<!--Gonggong-->
|<!--Eris-->
|<!--Minor planets-->
| <!--Other objects-->'''{{dp|Makemake}}'''<br />'''[[Astronomy:Haumea|Haumea]]'''<br />'''[[Astronomy:225088 Gonggong|Gonggong]]''',<br />'''[[Astronomy:50000 Quaoar|Quaoar]]'''
|-
! 500–1,000
|<!--Earth-->
|<!--Mars-->
|<!--Jupiter-->
| <!--Saturn-->'''[[Astronomy:Enceladus|Enceladus]]'''
|<!--Uranus-->
|<!--Neptune-->
|<!--Orcus-->
|<!--Pluto-->
|
|<!--Haumea-->
|<!--Quaoar-->
|<!--Makemake-->
|<!--Gonggong-->
| <!--Eris-->'''[[Astronomy:Dysnomia (moon)|Dysnomia]]'''
|<!--Minor planets-->
| <!--Other objects-->'''[[Astronomy:90377 Sedna|Sedna]]''', '''[[Astronomy:Ceres (dwarf planet)|Ceres]]''',<br />''[[Astronomy:120347 Salacia|Salacia]]'', '''[[Astronomy:90482 Orcus|Orcus]],'''<br />''[[Astronomy:2 Pallas|Pallas]]'', ''[[Astronomy:4 Vesta|Vesta]]'',<br />''[[Astronomy:174567 Varda|Varda]]'', ''[[Astronomy:28978 Ixion|Ixion]]''<br />{{small|many more TNOs}}
|-
! 250–500
|<!--Earth-->
|<!--Mars-->
|<!--Jupiter-->
| <!--Saturn-->'''Mimas'''<br />[[Astronomy:Hyperion (moon)|Hyperion]]
| <!--Uranus-->'''[[Astronomy:Miranda (moon)|Miranda]]'''
| <!--Neptune-->[[Astronomy:Proteus (moon)|Proteus]]<br />[[Astronomy:Nereid (moon)|Nereid]]
| <!--Orcus-->''[[Astronomy:Vanth (moon)|Vanth]]''
|<!--Pluto-->
|[[Astronomy:Actaea (moon)|Actaea]]
| <!--Haumea-->Hiʻiaka
|<!--Quaoar-->
|<!--Makemake-->
|<!--Gonggong-->
|<!--Eris-->
|<!--Minor planets-->''Varda I Ilmarë'' <br />Lempo&nbsp;II&nbsp;Hiisi
| <!--Other objects-->''[[Astronomy:10 Hygiea|10 Hygiea]]''<br />{{nowrap|''[[Astronomy:704 Interamnia|704 Interamnia]]''}}<br />[[Astronomy:87 Sylvia|87 Sylvia]]<br />[[Astronomy:47171 Lempo|47171 Lempo]]<br />{{small|and many others}}
|-
! 100–250
|<!--Earth-->
|<!--Mars-->
| <!--Jupiter-->[[Astronomy:Amalthea (moon)|Amalthea]]<br />[[Astronomy:Himalia (moon)|Himalia]]<br />[[Astronomy:Thebe (moon)|Thebe]]
| <!--Saturn-->[[Astronomy:Phoebe (moon)|Phoebe]]<br />[[Astronomy:Janus (moon)|Janus]]<br />[[Astronomy:Epimetheus (moon)|Epimetheus]]
| <!--Uranus-->[[Astronomy:Sycorax (moon)|Sycorax]]<br />[[Astronomy:Puck (moon)|Puck]]<br />[[Astronomy:Portia (moon)|Portia]]
| <!--Neptune-->[[Astronomy:Larissa (moon)|Larissa]]<br />[[Astronomy:Galatea (moon)|Galatea]]<br />[[Astronomy:Despina (moon)|Despina]]
|<!--Orcus-->
|<!--Pluto-->
|
| <!--Haumea-->Namaka
|<!--Quaoar-->
| <!--Makemake-->S/2015 (136472) 1
|<!--Gonggong-->
|<!--Eris-->
| <!--Minor planets-->[[Astronomy:(82075) 2000 YW134|S/2005&nbsp;(82075)]]&nbsp;1<br />[[Astronomy:79360 Sila–Nunam|Sila–Nunam]]&nbsp;I<br />[[Astronomy:65489 Ceto|Ceto]]&nbsp;I Phorcys<br />[[Astronomy:617 Patroclus|Patroclus]]&nbsp;I&nbsp;Menoetius<br />Lempo&nbsp;I&nbsp;Paha<br />{{small|~20 more moons of TNOs}}
| <!--Other objects-->[[Astronomy:3 Juno|3 Juno]]<br />[[Astronomy:15760 Albion|15760 Albion]]<br />[[Astronomy:5 Astraea|5 Astraea]]<br />[[Astronomy:617 Patroclus|617 Patroclus]]<br />[[Astronomy:42355 Typhon|42355 Typhon]]<br />{{small|and many others}}
|-
! 50–100
|<!--Earth-->
|<!--Mars-->
| <!--Jupiter-->[[Astronomy:Elara (moon)|Elara]]<br />[[Astronomy:Pasiphae (moon)|Pasiphae]]
| <!--Saturn-->[[Astronomy:Prometheus (moon)|Prometheus]]<br />[[Astronomy:Pandora (moon)|Pandora]]
| <!--Uranus-->[[Astronomy:Caliban (moon)|Caliban]]<br />[[Astronomy:Juliet (moon)|Juliet]]<br />[[Astronomy:Belinda (moon)|Belinda]]<br />[[Astronomy:Cressida (moon)|Cressida]]<br />[[Astronomy:Rosalind (moon)|Rosalind]]<br />[[Astronomy:Desdemona (moon)|Desdemona]]<br />[[Astronomy:Bianca (moon)|Bianca]]
| <!--Neptune-->[[Astronomy:Thalassa (moon)|Thalassa]]<br />[[Astronomy:Halimede (moon)|Halimede]]<br />[[Astronomy:Neso (moon)|Neso]]<br />[[Astronomy:Naiad (moon)|Naiad]]
|<!--Orcus-->
|<!--Pluto-->
|
|<!--Haumea-->
| <!--Quaoar-->Weywot
|<!--Makemake-->
| <!--Gonggong-->Xiangliu (probably)
|<!--Eris-->
| <!--Minor planets-->[[Astronomy:90 Antiope|90 Antiope]]&nbsp;I<br />[[Astronomy:42355 Typhon|Typhon]]&nbsp;I&nbsp;Echidna<br />[[Astronomy:58534 Logos|Logos]]&nbsp;I&nbsp;Zoe<br />{{small|5 more moons of TNOs}}<!--- No TNO moons below Zoe's size (66 km) are known--->
| <!--Other objects-->[[Astronomy:90 Antiope|90 Antiope]]<br />[[Astronomy:58534 Logos|58534 Logos]]<br />[[Astronomy:253 Mathilde|253 Mathilde]]<br />{{small|and many others}}
|-
! 25–50
|<!--Earth-->
|<!--Mars-->
| <!--Jupiter-->[[Astronomy:Carme (moon)|Carme]]<br />[[Astronomy:Metis (moon)|Metis]]<br />[[Astronomy:Sinope (moon)|Sinope]]<br />[[Astronomy:Lysithea (moon)|Lysithea]]<br />[[Astronomy:Ananke (moon)|Ananke]]
| <!--Saturn-->Siarnaq<br />[[Astronomy:Helene (moon)|Helene]]<br />[[Astronomy:Albiorix (moon)|Albiorix]]<br />[[Astronomy:Atlas (moon)|Atlas]]<br />[[Astronomy:Pan (moon)|Pan]]
| <!--Uranus-->[[Astronomy:Ophelia (moon)|Ophelia]]<br />[[Astronomy:Cordelia (moon)|Cordelia]]<br />[[Astronomy:Setebos (moon)|Setebos]]<br />[[Astronomy:Prospero (moon)|Prospero]]<br />[[Astronomy:Perdita (moon)|Perdita]]<br />[[Astronomy:Stephano (moon)|Stephano]]
| <!--Neptune-->[[Astronomy:Sao (moon)|Sao]]<br />Laomedeia<br />[[Astronomy:Psamathe (moon)|Psamathe]]<br />[[Astronomy:Hippocamp (moon)|Hippocamp]]
|<!--Orcus-->
| <!--Pluto-->Hydra<br />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|Kalliope I Linus}}
| <!--Other objects-->[[Astronomy:1036 Ganymed|1036 Ganymed]]<br />[[Astronomy:243 Ida|243 Ida]]<br />{{small|and many others}}
|-
! 10–25
|<!--Earth-->
| <!--Mars-->[[Astronomy:Phobos (moon)|Phobos]]<br />[[Astronomy:Deimos (moon)|Deimos]]
| <!--Jupiter-->[[Astronomy:Leda (moon)|Leda]]<br />[[Astronomy:Adrastea (moon)|Adrastea]]
| <!--Saturn-->[[Astronomy:Telesto (moon)|Telesto]]<br />Paaliaq<br />[[Astronomy:Calypso (moon)|Calypso]]<br />[[Astronomy:Ymir (moon)|Ymir]]<br />[[Astronomy:Kiviuq (moon)|Kiviuq]]<br />[[Astronomy:Tarvos (moon)|Tarvos]]<br />[[Astronomy:Ijiraq (moon)|Ijiraq]]<br />[[Astronomy:Erriapus|Erriapus]]
| <!--Uranus-->[[Astronomy:Mab (moon)|Mab]]<br />[[Astronomy:Cupid (moon)|Cupid]]<br />[[Astronomy:Francisco (moon)|Francisco]]<br />[[Astronomy:Ferdinand (moon)|Ferdinand]]<br />[[Astronomy:Margaret (moon)|Margaret]]<br />[[Astronomy:Trinculo (moon)|Trinculo]]
|<!--Neptune-->
|<!--Orcus-->
| <!--Pluto-->Kerberos<br />Styx
|
|<!--Haumea-->
|<!--Quaoar-->
|<!--Makemake-->
|<!--Gonggong-->
|<!--Eris-->
| <!--Minor planets-->[[Astronomy:762 Pulcova|762 Pulcova]] I<br />{{nowrap|Sylvia I Romulus}}<br />[[Astronomy:624 Hektor|624 Hektor]]&nbsp;I&nbsp;Skamandrios<br />{{nowrap|Eugenia I Petit-Prince}}<br />[[Astronomy:121 Hermione|121 Hermione]]&nbsp;I<br />[[Astronomy:283 Emma|283 Emma]]&nbsp;I<br />[[Astronomy:1313 Berna|1313 Berna]]&nbsp;I<br />[[Astronomy:107 Camilla|107 Camilla]] I
| <!--Other objects-->[[Astronomy:433 Eros|433 Eros]]<br />[[Astronomy:1313 Berna|1313 Berna]]<br />{{small|and many others}}
|-
! < 10
|<!--Earth-->
|<!--Mars-->
| <!--Jupiter-->[[Astronomy:Moons of Jupiter|''95 moons'']]
| <!--Saturn-->[[Astronomy:Moons of Saturn|''146 moons'']]
|<!--Uranus-->
|<!--Neptune-->
|<!--Orcus-->
|<!--Pluto-->
|
|<!--Haumea-->
|<!--Quaoar-->
|<!--Makemake-->
|<!--Gonggong-->
|<!--Eris-->
| <!--Minor planets-->{{nowrap|Sylvia II Remus}}<br />{{nowrap|Ida I Dactyl}}<br />{{small|and many others}}
| <!--Other objects-->many
|}

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

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

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

==References==
{{reflist|refs=

<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
 | author=Wm. Robert Johnston
 | url=http://www.johnstonsarchive.net/astro/asteroidmoons.html
 | access-date=22 October 2018}}</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>

}} <!-- end of reflist -->

==External links==

===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===
* [http://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}}

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

{{Sourceattribution|Natural satellite}}