Of theSolar System's eight planets and itsnine most likely dwarf planets, six planets and seven dwarf planets are known to be orbited by at least 431natural satellites, or moons. At least19 of them are large enough to be gravitationally rounded; of these, all are covered by acrust ofice except for Earth'sMoon and Jupiter'sIo.[1] Several of the largest ones are inhydrostatic equilibrium and would therefore be considereddwarf planets orplanets if they were in direct orbit around the Sun and not in their current states (orbiting planets or dwarf planets).
Moons are classed into two separate categories according to their orbits:regular moons, which haveprograde orbits (they orbit in the direction of their planets' rotation) and lie close to the plane of their equators, andirregular moons, whose orbits can be pro- orretrograde (against the direction of their planets' rotation) and often lie at extreme angles to their planets' equators. Irregular moons are probably minor planets that have been captured from surrounding space. Most irregular moons are less than 10 kilometres (6.2 mi) in diameter.
The earliest published discovery of a moon other than Earth's was byGalileo Galilei, who discovered the fourGalilean moons orbitingJupiter in 1610. Over the following three centuries, only a few more moons were discovered. Missions to other planets in the 1970s, most notably theVoyager 1 and2 missions, saw a surge in the number of moons detected, and observations since the year 2000, using mostly large, ground-basedoptical telescopes, have discovered many more, all of which are irregular.
Some moons, minor planets and comets of the Solar System to scale (major planets not to scale)Selected moons, with Earth to scale. Nineteen moons are large enough to be round, and two, Titan and Triton, have substantial atmospheresThe number of moons discovered in each year until March 2025The number of moons announced in each year until March 2025
Mercury, the smallest and innermost planet, has no moons, or at least none that can be detected to a diameter of 1.6 km (1.0 mi).[2] For a very short time in 1974, Mercurywas thought to have a moon.
Earth has oneMoon, the largest moon of anyrocky planet in the Solar System and the largest body typically described as a moon that orbits anything in hydrostatic equilibrium in relation to the primary object by mass and diameter other than Charon and Pluto. Earth also has more than 20 knownco-orbitals, including theasteroids3753 Cruithne and469219 Kamoʻoalewa, and the occasionaltemporary satellite, like2020 CD3; however, since they do not permanently orbit Earth, they are not considered moons. (SeeOther moons of Earth andQuasi-satellite.)
Mars hastwo known moons,Phobos andDeimos ("fear" and "dread", after attendants ofAres, the Greek god of war, equivalent to the Roman Mars). Searches for more satellites have been unsuccessful, putting the maximum radius of any other satellites at 90 m (100 yd).[4]
Jupiter has97 moons with known orbits announced;[5] 72 of them have received permanent designations, and 57 have been named. Its eight regular moons are grouped into theplanet-sizedGalilean moons and the far smallerAmalthea group. They were named after lovers of Zeus, the Greek equivalent of Jupiter. Among them isGanymede, the largest and most massive moon in the Solar System. The rest are irregular moons, which are organized into two categories:prograde andretrograde. The prograde satellites consist of theHimalia group and three others in groups of one. The retrograde moons are grouped into theCarme,Ananke andPasiphae groups.
Saturn has274 moons with known orbits announced; 66 of them have received permanent designations, and 63 have been named. Most of them are quite small. Seven moons are large enough to be inhydrostatic equilibrium, includingTitan, the second largest moon in the Solar System. Including these large moons, 24 of Saturn's moons are regular, and traditionally named afterTitans or other figures associated with the mythologicalSaturn. The remaining moons are irregular, and classified by their orbital characteristics intoInuit,Norse, andGallic groups, and their names are chosen from the corresponding mythologies the groups are named after. Therings of Saturn are made up of icy objects ranging in size from one centimetre to hundreds of metres, each of which is on its own orbit about the planet. Thus, a precise number of Saturnian moons cannot be given, as there is no objective boundary between the countless small anonymous objects that form Saturn's ring system and the larger objects that have been named as moons. At least 150 "moonlets" embedded in the rings have been detected by the disturbance they create in the surrounding ring material, though this is thought to be only a small sample of the total population of such objects.
Uranus has29 known moons announced, five of which are massive enough to have achieved hydrostatic equilibrium. There are 14 moons that orbit withinUranus's ring system, and another ten outer irregular moons. Unlike most planetary moons, which are named from antiquity, all the moons of Uranus are named after characters from the works ofShakespeare andAlexander Pope's workThe Rape of the Lock.
Neptune has16 known moons announced; the largest,Triton, accounts for more than 99.5 percent of all the mass orbiting the planet. Triton is large enough to have achieved hydrostatic equilibrium, but, uniquely for a large moon, has a retrograde orbit, suggesting it was a dwarf planet that was captured. Neptune also has seven known inner regular satellites, and eight outer irregular satellites.
Pluto, adwarf planet, is confirmed to havefive moons. Its largest moonCharon, named after the ferryman who took souls across theRiver Styx, is more than half as large as Pluto itself, and large enough to orbit a point outside Pluto's surface. In effect, each orbits the other, forming abinary system informally referred to as adouble-dwarf-planet. Pluto's four other moons,Nix,Hydra,Kerberos andStyx are far smaller and orbit the Pluto–Charon system.[6]
Among the other dwarf planets,Ceres has no known moons. It is 90 percent certain that Ceres has no moons larger than 1 km in size, assuming that they would have the samealbedo as Ceres itself.[7]Eris has one large known moon,Dysnomia. Accurately determining its size is difficult: one indicative estimate of its radius is350±57.5 km.[8]
Two objects were named as dwarf planets, under the expectation that they would prove to be so (though this remains uncertain).Haumea has two moons,Hiʻiaka andNamaka, of radii ~195 and ~100 km, respectively.[9]Makemake has one moon, announced in April 2016.
A number of other objects in theKuiper belt andscattered disk may turn out to be dwarf planets.Orcus,Quaoar,Gonggong, andSedna are generally agreed to be dwarf planets among astronomers, and all but Sedna are known to have moons.[10] A number of other smaller objects, such asHuya,Salacia,Uni,Varda, andChiminigagua, also have moons, although their dwarf planethood is more doubtful.
Due to Earth's varying distance from these planets (as well as their distance to the Sun), the limits at which we are able to detect new moons are very inconsistent. As the below graph demonstrates, the maximumabsolute magnitude (total inherent brightness, abbreviated H) of moons we have detected around planets occurs at H = 18 for Jupiter, H = 17 for Saturn, H = 14 for Uranus, and H = 12 for Neptune. Smaller moons may (and most likely do) exist around each of these planets, but are currently undetectable from Earth. Although spacecraft have visited all of these planets, Earth-based telescopes continue to outperform them in moon-detection ability due to their greater availability for wide-field surveys.[citation needed]
This is a list of the recognized moons of the planets and of the largest potential dwarf planets of the Solar System, ordered by their officialRoman numeral designations. Moons that do not yet have official Roman numeral designations (because their orbits are not yet known well enough) are listed after those that do.
The 19 moons that are known to belarge enough to have been rounded by their own gravity are listed inbold. The seven largest moons, which are larger than any of the known dwarf planets, are listed inbold and italic. Sidereal period differs from semi-major axis because a moon's speed depends both on the mass of its primary and its distance from it.
^Bieryla, Allyson; Parker, J. W. (December 2006). "Search for Satellites around Ceres".2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #25.02; Bulletin of the American Astronomical Society.38: 933.Bibcode:2006AAS...209.2502B.
^abJohnston, W. R. (30 December 2008)."(136199) Eris and Dysnomia".Johnston's Archive.Archived from the original on 11 May 2020. Retrieved1 December 2016.
^Johnston, Wm. Robert (8 November 2025)."Asteroids with Satellites". Johnston's Archive.Archived from the original on 18 December 2019. Retrieved11 November 2025.
^Proudfoot, Benjamin; Nolthenius, Richard; Holler, Bryan J.; Souza-Feliciano, Ana Carolina de; Rommel, Flavia L.; Collyer, Cameron; Grundy, Will M.; Fernández-Valenzuela, Estela (10 November 2025), "Orbital Characterization of a Newly Discovered Small Satellite around Quaoar",The Astrophysical Journal Letters,993 (2): L38,arXiv:2511.07370,Bibcode:2025ApJ...993L..38P,doi:10.3847/2041-8213/ae1585
^"MPEC 2020-V19: S/2003 J 9".Minor Planet Electronic Circular. Minor Planet Center. 5 November 2020.Archived from the original on 5 November 2020. Retrieved5 November 2020.
^"MPEC 2020-V10: S/2003 J 16".Minor Planet Electronic Circular. Minor Planet Center. 4 November 2020.Archived from the original on 4 November 2020. Retrieved4 November 2020.
^C. Porco & the Cassini Imaging Team (18 July 2007)."S/ 2007 S 4".IAU Circular (8857).Archived from the original on 27 March 2012. Retrieved8 January 2011.
^Green, Daniel W. E. (19 August 2025)."CBET 5593: S/2025 U 1". Central Bureau Electronic Telegram. Central Bureau for Astronomical Telegrams. Retrieved 19 August 2025.
^abD. C. Fabrycky; M. J. Holman; D. Ragozzine; M. E. Brown; T. A. Lister; D. M. Terndrup; J. Djordjevic; E. F. Young; L. A. Young; R. R. Howell (2008). "Mutual Events of 2003 EL61 and its Inner Satellite".AAS DPS Conference 2008.40: 36.08.Bibcode:2008DPS....40.3608F.
^abJohnston, Wm. Robert (21 September 2014)."(50000) Quaoar and Weywot". Johnston's Archive.Archived from the original on 5 September 2019. Retrieved20 June 2023.
^abKiss, Csaba; Marton, Gabor; Parker, Alex H.; Grundy, Will; Farkas-Takacs, Aniko; Stansberry, John; Pal, Andras; Muller, Thomas; Noll, Keith S.; Schwamb, Megan E.; Barr, Amy C.; Young, Leslie A.; Vinko, Jozsef (October 2018). "The mass and density of the dwarf planet (225088) 2007 OR10".Icarus.334:3–10.arXiv:1903.05439.Bibcode:2018DPS....5031102K.doi:10.1016/j.icarus.2019.03.013.S2CID119370310. 311.02. Initial publication at the American Astronomical Society DPS meeting #50, with the publication ID 311.02
^Apparent magnitudes sourced from the moon's respective Wikipedia page, some may be taken from German Wikipedia articles that include more information, some may be calculated based on absolute magnitudes.