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The
Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...
's planets, and its most likely dwarf planets, are known to be orbited by at least 221
natural satellite A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body (or sometimes another natural satellite). Natural satellites are often colloquially referred to as ''moons'' ...
s, or moons. At least 20 of them are large enough to be gravitationally rounded; of these, all are covered by a crust of
ice Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaq ...
except for Earth's
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
and Jupiter's Io.Ice in the Solar System – NASA
/ref> Several of the largest ones are in
hydrostatic equilibrium In fluid mechanics, hydrostatic equilibrium (hydrostatic balance, hydrostasy) is the condition of a fluid or plastic solid at rest, which occurs when external forces, such as gravity, are balanced by a pressure-gradient force. In the planetary ...
and would therefore be considered
dwarf planet A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to p ...
s or
planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...
s if they were in direct orbit around the Sun and not in their current states (orbiting planets or dwarf planets). Moons are classed in two separate categories according to their orbits: regular moons, which have
prograde orbit Retrograde motion in astronomy is, in general, orbital or rotational motion of an object in the direction opposite the rotation of its primary, that is, the central object (right figure). It may also describe other motions such as precession or ...
s (they orbit in the direction of their planets' rotation) and lie close to the plane of their equators, and irregular moons, whose orbits can be pro- or retrograde (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 in diameter. The earliest published discovery of a moon other than the Earth's was by
Galileo Galilei Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He was ...
, who discovered the four
Galilean moons The Galilean moons (), or Galilean satellites, are the four largest moons of Jupiter: Io, Europa, Ganymede, and Callisto. They were first seen by Galileo Galilei in December 1609 or January 1610, and recognized by him as satellites of Jupite ...
orbiting
Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandth th ...
in 1610. Over the following three centuries only a few more moons were discovered. Missions to other planets in the 1970s, most notably the ''
Voyager 1 ''Voyager 1'' is a space probe launched by NASA on September 5, 1977, as part of the Voyager program to study the outer Solar System and interstellar space beyond the Sun's heliosphere. Launched 16 days after its twin ''Voyager 2'', ''Voya ...
'' and '' 2'' missions, saw a surge in the number of moons detected, and observations since the year 2000, using mostly large, ground-based
optical telescope An optical telescope is a telescope that gathers and focuses light mainly from the visible part of the electromagnetic spectrum, to create a magnified image for direct visual inspection, to make a photograph, or to collect data through electro ...
s, have discovered many more, all of which are irregular. __TOC__


Moons by primary

Mercury, the smallest and innermost planet, has no moons, or at least none that can be detected to a diameter of . For a very short time in 1974, Mercury was thought to have a moon.
Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...
also has no moons, though reports of a moon around Venus have circulated since the 17th century.
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surface ...
has one
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
, the largest moon of any
rocky planet A terrestrial planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun: Mercury, ...
in the Solar System. Earth also has more than 20 known
co-orbital In astronomy, a co-orbital configuration is a configuration of two or more astronomical objects (such as asteroids, moons, or planets) orbiting at the same, or very similar, distance from their primary, i.e. they are in a 1:1 mean-motion resonance ...
s, including the
asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...
s
3753 Cruithne 3753 Cruithne is a Q-type, Aten asteroid in orbit around the Sun in 1:1 orbital resonance with Earth, making it a co-orbital object. It is an asteroid that, relative to Earth, orbits the Sun in a bean-shaped orbit that effectively describes a ...
and
469219 Kamoʻoalewa 469219 Kamoʻoalewa (), provisionally designated , is a very small asteroid, fast rotator and near-Earth object of the Apollo group, approximately in diameter. At present it is a quasi-satellite of Earth, and currently the smallest, closest, ...
, and the occasional temporary satellite, like 2020 CD3; however, since they do not permanently orbit Earth, they are not considered moons. (See Other moons of Earth and
Quasi-satellite A quasi-satellite is an object in a specific type of co-orbital configuration (1:1 orbital resonance) with a planet (or dwarf planet) where the object stays close to that planet over many orbital periods. A quasi-satellite's orbit around the Sun ...
.)
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin atmosp ...
has two known moons, Phobos and Deimos ("fear" and "dread", after attendants of
Ares Ares (; grc, Ἄρης, ''Árēs'' ) is the Greek god of war and courage. He is one of the Twelve Olympians, and the son of Zeus and Hera. The Greeks were ambivalent towards him. He embodies the physical valor necessary for success in war b ...
, 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 .
Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandth th ...
has 82 moons with known orbits; 72 of them have received permanent designations, and 57 have been named. Its eight regular moons are grouped into the planet-sized
Galilean moons The Galilean moons (), or Galilean satellites, are the four largest moons of Jupiter: Io, Europa, Ganymede, and Callisto. They were first seen by Galileo Galilei in December 1609 or January 1610, and recognized by him as satellites of Jupite ...
and the far smaller Amalthea group. They are named after lovers of Zeus, the Greek equivalent of Jupiter. Its 74 known irregular moons are organized into two categories: prograde and retrograde. The prograde satellites consist of the
Himalia group The Himalia group is a group of prograde irregular satellites of Jupiter that follow similar orbits to Himalia and are thought to have a common origin. Scott S. Sheppard, David C. Jewitt ''An abundant population of small irregular satellites a ...
and three others in groups of one. The retrograde moons are grouped into the Carme,
Ananke In ancient Greek religion, Ananke (; grc, Ἀνάγκη), from the common noun , "force, constraint, necessity") is the personification of inevitability, compulsion and necessity. She is customarily depicted as holding a spindle. One of the G ...
and Pasiphae groups.
Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...
has 83 moons with known orbits; 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 in
hydrostatic equilibrium In fluid mechanics, hydrostatic equilibrium (hydrostatic balance, hydrostasy) is the condition of a fluid or plastic solid at rest, which occurs when external forces, such as gravity, are balanced by a pressure-gradient force. In the planetary ...
, including Titan, the second largest moon in the Solar System. Including these large moons, 24 of Saturn's moons are regular, and traditionally named after
Titans In Greek mythology, the Titans ( grc, οἱ Τῑτᾶνες, ''hoi Tītânes'', , ''ho Tītân'') were the pre-Olympian gods. According to the ''Theogony'' of Hesiod, they were the twelve children of the primordial parents Uranus (Sky) and Gai ...
or other figures associated with the mythological
Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...
. The remaining 59, all small, are irregular, and classified by their orbital characteristics into
Inuit Inuit (; iu, ᐃᓄᐃᑦ 'the people', singular: Inuk, , dual: Inuuk, ) are a group of culturally similar indigenous peoples inhabiting the Arctic and subarctic regions of Greenland, Labrador, Quebec, Nunavut, the Northwest Territories, and ...
, Norse, and Gallic groups, and their names are chosen from the corresponding mythologies the groups are named after. The
rings of Saturn The rings of Saturn are the most extensive ring system of any planet in the Solar System. They consist of countless small particles, ranging in size from micrometers to meters, that orbit around Saturn. The ring particles are made almost entire ...
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 "
moonlet A moonlet, minor moon, minor natural satellite, or minor satellite is a particularly small natural satellite orbiting a planet, dwarf planet, or other minor planet. Up until 1995, moonlets were only hypothetical components of Saturn's F-ring ...
s" 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 Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus ( Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars), grandfather of Zeus (Jupiter) and father of Cro ...
has 27 moons, five of which are massive enough to have achieved hydrostatic equilibrium. There are 13 moons that orbit within Uranus's ring system, and another nine outer irregular moons. Unlike most planetary moons, which are named from antiquity, all the moons of Uranus are named after characters from the works of
Shakespeare William Shakespeare ( 26 April 1564 – 23 April 1616) was an English playwright, poet and actor. He is widely regarded as the greatest writer in the English language and the world's pre-eminent dramatist. He is often called England's nation ...
and
Alexander Pope Alexander Pope (21 May 1688 O.S. – 30 May 1744) was an English poet, translator, and satirist of the Enlightenment era who is considered one of the most prominent English poets of the early 18th century. An exponent of Augustan literature, ...
's work ''
The Rape of the Lock ''The Rape of the Lock'' is a mock-heroic narrative poem written by Alexander Pope. One of the most commonly cited examples of high burlesque, it was first published anonymously in Lintot's ''Miscellaneous Poems and Translations'' (May 1712 ...
''.
Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
has 14 moons; 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 six outer irregular satellites.
Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Sun. It is the largest k ...
, a
dwarf planet A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to p ...
, has five moons. Its largest moon
Charon In Greek mythology, Charon or Kharon (; grc, Χάρων) is a psychopomp, the ferryman of Hades, the Greek underworld. He carries the souls of those who have been given funeral rites across the rivers Acheron and Styx, which separate the wor ...
, named after the ferryman who took souls across the
River Styx In Greek mythology, Styx (; grc, Στύξ ) is a river that forms the boundary between Earth (Gaia) and the Underworld. The rivers Acheron, Cocytus, Lethe, Phlegethon, and Styx all converge at the centre of the underworld on a great marsh, ...
, 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 a
binary system A binary system is a system of two astronomical bodies which are close enough that their gravitational attraction causes them to orbit each other around a barycenter ''(also see animated examples)''. More restrictive definitions require that thi ...
informally referred to as a double-dwarf-planet. Pluto's four other moons, Nix, Hydra, Kerberos and
Styx In Greek mythology, Styx (; grc, Στύξ ) is a river that forms the boundary between Earth (Gaia) and the Underworld. The rivers Acheron, Cocytus, Lethe, Phlegethon, and Styx all converge at the centre of the underworld on a great marsh, whic ...
are far smaller and orbit the Pluto–Charon system.. ''a, i, e'' pe
JPL
(site updated 2008 Aug 25)
Among the other dwarf planets, 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 same
albedo Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...
as Ceres itself. has one large known moon, Dysnomia. Accurately determining its size is difficult: one indicative estimate of its radius is . Two objects were named as dwarf planets, under the expectation that they would prove to be so (though this remains uncertain). has two moons, Hiʻiaka and Namaka, of radii ~195 and ~100 km, respectively. has one moon, discovered in April 2016. A number of other objects in the
Kuiper belt The Kuiper belt () is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 ti ...
and
scattered disk The scattered disc (or scattered disk) is a distant circumstellar disc in the Solar System that is sparsely populated by icy small solar system bodies, which are a subset of the broader family of trans-Neptunian objects. The scattered-disc obj ...
may turn out to be dwarf planets. , , , and are generally agreed to be dwarf planets among astronomers, and all but Sedna are known to have moons. A number of other smaller objects, such as , , and , also have moons, although their dwarf planethood is more doubtful. This list includes all objects with best estimated diameter above 700 km, including whose satellite has not been seen since its initial discovery. , 365 asteroid moons and 128 trans-Neptunian moons (including those of Pluto and the other dwarf planets) had been discovered. : : : 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 is very inconsistent. As the below graph demonstrates, the
absolute magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse logarithmic astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if it ...
(total inherent brightness, abbreviated H) of moons we have detected around planets peaks at H = 17 for Jupiter, H = 16 for Saturn, H = 13 for Uranus, and H = 11 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.


List

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 official Roman 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 20 moons that are known to be large enough to have been rounded by their own gravity are listed in bold. The seven largest moons, which are larger than any of the known
dwarf planet A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to p ...
s, are listed in ''bold 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. Angular size from the parent surface actually might differ much depending on the moon location at the given moment and the point where it is observed from the parent surface (and some of these parents might not have a solid surface); the observation point matters especially for moons orbiting very near their parents e.g.
Naiad In Greek mythology, the naiads (; grc-gre, ναϊάδες, naïádes) are a type of female spirit, or nymph, presiding over fountains, wells, springs, streams, brooks and other bodies of fresh water. They are distinct from river gods, who ...
is at average below two times parent radius from the center of
Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
and
Cordelia Cordelia is a feminine given name. It was borne by the tragic heroine of Shakespeare's ''King Lear'' (1606), a character based on the legendary queen Cordelia. The name is of uncertain origin. It is popularly associated with Latin '' cor'' (geni ...
is at average below two times parent radius from the center of
Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus ( Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars), grandfather of Zeus (Jupiter) and father of Cro ...
.


Unconfirmed satellites

There are several moons in the
Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...
where their existence is questioned, or they may be not orbiting around their supposed parent planet. Only
Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...
and
Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
currently have unconfirmed moons.


See also


References

* {{DEFAULTSORT:List Of Moons *