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Encyclopedia > Natural satellite

A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called the primary. Technically, the term natural satellite could refer to a planet orbiting a star, or a dwarf galaxy orbiting a major galaxy, but it is normally synonymous with moon and used to identify non-artificial satellites of planets, dwarf planets, and minor planets. (There are no known natural satellites of moons.) See lists of astronomical objects for a list of the various lists of astronomical objects in Wikipedia. ... Two bodies with a slight difference in mass orbiting around a common barycenter. ... This article is about the astronomical term. ... This article is about the astronomical object. ... A dwarf galaxy is a small galaxy composed of up to several billion stars, a small number compared to our own Milky Ways 200-400 billion stars. ... This article is about artificial satellites. ... Artists impression of Pluto (background) and Charon (foreground). ... Minor planets, or asteroids or planetoids, are minor celestial bodies of the Solar system orbiting the Sun (mostly Small solar system bodies) that are smaller than major planets, but larger than meteoroids (commonly defined as being 10 meters across or less[1]), and that are not comets. ...


Two hundred and forty bodies, all in the Solar System, are classified as moons. They include 166 orbiting the eight planets,[1] 4 orbiting dwarf planets, and dozens more orbiting small solar system bodies. Other stars and their planets are very likely to have natural satellites, although none have yet been observed. This article is about the Solar System. ... It has been suggested that minor planet be merged into this article or section. ...


The large gas giants have extensive systems of moons, including half a dozen comparable in size to Earth's moon: the four Galilean moons, Saturn's Titan, and Neptune's Triton. Saturn has an additional six mid-sized moons massive enough to have achieved hydrostatic equilibrium, and Uranus has five. Of the inner planets, Mercury and Venus have no moons at all; Earth has one large moon (the Moon); and Mars has two tiny moons, Phobos and Deimos. Among the dwarf planets, Ceres has no moons (though many objects in the asteroid belt do), Eris has one, Dysnomia, and Pluto has three known satellites, Nix, Hydra, and a large companion called Charon. The Pluto-Charon system is unusual in that the center of mass lies in open space between the two, a characteristic of a double planet system. This article does not cite any references or sources. ... This article is about Earth as a planet. ... Jupiters 4 Galilean moons, in a composite image comparing their sizes and the size of Jupiter (Great Red Spot visible). ... This article is about the planet. ... Titan (, from Ancient Greek Τῑτάν) or Saturn VI is the largest moon of Saturn and the only moon known to have a dense atmosphere. ... For other uses, see Neptune (disambiguation). ... Triton (trye-tÉ™n, IPA: , Greek Τρίτων), or Neptune I, is the planet Neptunes largest moon. ... Hydrostatic equilibrium occurs when compression due to gravity is balanced by a pressure gradient which creates a pressure gradient force in the opposite direction. ... For other uses, see Uranus (disambiguation). ... This article is about the planet. ... For other uses, see Venus (disambiguation). ... This article is about Earths moon. ... Adjectives: Martian Atmosphere Surface pressure: 0. ... Phobos (IPA: or [ˈfoÊŠ.bÉ™s]) (systematic designation: ) is the larger and closer of Mars two moons (the other being Deimos). ... Deimos (IPA or ; Greek Δείμος: Dread), is the smaller and outermost of Mars’ two moons, named after Deimos from Greek Mythology. ... Spectral type: G[8] Absolute magnitude: 3. ... Absolute magnitude: −1. ... Dysnomia (officially designated (136199) Eris I Dysnomia) is a moon of the dwarf planet Eris. ... For other uses, see Pluto (disambiguation). ... Nix (formerly known as S/2005 P 2), is a natural satellite of Pluto. ... Hydra (formerly known as S/2005 P 1) is a natural satellite of Pluto. ... Charon (shair-É™n or kair-É™n (key), IPA , Greek Χάρων), discovered in 1978, is, depending on the definition employed, either the largest moon of Pluto or one member of a double dwarf planet with Pluto being the other member. ... In physics, the center of mass of a system of particles is a specific point at which, for many purposes, the systems mass behaves as if it was concentrated. ... Pluto and Charon are sometimes informally considered to be a double (dwarf) planet. ...

Selected moons, with the Earth to scale. Nineteen moons are large enough to be round, and one, Titan, has a substantial atmosphere.
Selected moons, with the Earth to scale. Nineteen moons are large enough to be round, and one, Titan, has a substantial atmosphere.

Contents

Image File history File links Size of this preview: 800 × 565 pixel Image in higher resolution (1700 × 1200 pixel, file size: 330 KB, MIME type: image/jpeg) Wikipedia:Featured picture candidates/Moons of solar system Changes from original Deuar Charon was far too small, and Image:Charon_plutoface. ... Image File history File links Size of this preview: 800 × 565 pixel Image in higher resolution (1700 × 1200 pixel, file size: 330 KB, MIME type: image/jpeg) Wikipedia:Featured picture candidates/Moons of solar system Changes from original Deuar Charon was far too small, and Image:Charon_plutoface. ...

Origin

The natural satellites orbiting relatively close to the planet on prograde orbits (regular satellites) are generally believed to have been formed out of the same collapsing region of the protoplanetary disk that gave rise to its primary. In contrast, irregular satellites (generally orbiting on distant, inclined, eccentric and/or retrograde orbits) are thought to be captured asteroids possibly further fragmented by collisions. The Earth's Moon[2] and possibly Charon[3] are exceptions among large bodies in that they are believed to have originated by the collision of two large proto-planetary objects (see the giant impact hypothesis). The material that would have been placed in orbit around the central body is predicted to have reaccreted to form one or more orbiting moons. As opposed to planetary-sized bodies, asteroid moons are thought to commonly form by this process. Triton is another exception, which although large and in a close, circular orbit, is thought to be a captured dwarf planet. A protoplanetary disc (also protoplanetary disk, proplyd) is an accretion disc surrounding a T Tauri star. ... In astronomy, an irregular satellite is a natural satellite following a distant, inclined, often retrograde orbit and believed to be captured as opposed to a regular satellite, formed in situ. ... Inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit and is the angular distance of the orbital plane from the plane of the reference (usually planets equator or the ecliptic), stated in degrees. ... (This page refers to eccitricity in astrodynamics. ... This article is about retrograde motion. ... For other uses, see Asteroid (disambiguation). ... The Big Splash redirects here. ... 243 Ida and its moon Dactyl An asteroid moon is an asteroid that orbits another asteroid. ... Artists impression of Pluto (background) and Charon (foreground). ...


Geological activity

Of the nineteen known moons massive enough to have lapsed into hydrostatic equilibrium, several remain geologically active today. Io is the most volcanically active body in the Solar System, while Triton and Enceledus have geysers. Titan and Triton have significant atmospheres; Titan also has methane lakes, and presumably rain. Four of the largest moons, Europa, Ganymede, Callisto, and Titan, are thought to have subsurface oceans of liquid water, while smaller Enceladus may have localized subsurface water. Many other moons, such as Tethys, show evidence of past geological activity. Atmosphere Surface pressure: trace Composition: 90% sulfur dioxide Io (eye-oe, IPA: , Greek Ῑώ) is the innermost of the four Galilean moons of Jupiter and, with a diameter of 3,642 kilometers, is the fourth largest moon in the Solar System. ... Triton (trye-tÉ™n, IPA: , Greek Τρίτων), or Neptune I, is the planet Neptunes largest moon. ... Apparent magnitude 11. ... Titan (, from Ancient Greek Τῑτάν) or Saturn VI is the largest moon of Saturn and the only moon known to have a dense atmosphere. ... Apparent magnitude: 5. ... This article is about the natural satellite of Jupiter. ... There is also an asteroid named 204 Kallisto. ... Not to be confused with the asteroid named 17 Thetis. ...


Orbital characteristics

Tidal locking

The regular natural satellites in the solar system are tidally locked to their primaries, meaning that the same side of the moon always faces the planet. The only known exception is Saturn's moon Hyperion, which rotates chaotically because of the gravitational influence of Titan. Tidal locking makes one side of an astronomical body always face another, like the Moon facing the Earth. ... This article is about the planet. ... Hyperion (IPA: , Greek Ὑπερίων) is a moon of Saturn discovered by William Cranch Bond, George Phillips Bond and William Lassell in 1848. ...


In contrast, the outer moons of the gas giants (irregular satellites) are too far away to have become locked. For example, Jupiter's moon Himalia, Saturn's moon Phoebe, and Neptune's moon Nereid have rotation period in the range of ten hours, while their orbital periods are hundreds of days. Atmospheric pressure 0 kPa Himalia (hye-mal-ee-a, also hi-mahl-ee-a, IPA , ; Greek ‘Ιμαλíα) is a moon of Jupiter. ... For other meanings see Phoebe. ... Nereid (IPA: , IPA: , Greek Νηρηίδα), or Neptune II, is a moon of Neptune. ...


Satellites of satellites

Artist impression of Rhea's rings
Artist impression of Rhea's rings

No moons of moons (natural satellites that orbit the natural satellite of another body) are known. In most cases, the tidal effects of the primary would make such a system unstable.


However, calculations performed after the recent detection [4] of a possible ring system around Saturn's moon Rhea indicate that Rhean orbits would be stable. Furthermore, the suspected rings are thought to be narrow,[5] a phenomenon normally associated with shepherd moons. Atmosphere none Rhea (ree-a, Greek ‘Ρέα) is the second largest moon of Saturn and was discovered in 1672 by Giovanni Domenico Cassini. ...


Trojan satellites

Two moons are known to have small companions at their L4 and L5 Lagrangian points, sixty degrees ahead and behind the body in its orbit. These companions are called Trojan moons, as their orbits are analogous to the Trojan asteroids of Jupiter. The Trojan moons are Telesto and Calypso, which are the leading and following companions respectively of Tethys; and Helene and Polydeuces, the leading and following companions of Dione. A contour plot of the effective potential (the Hills Surfaces) of a two-body system (the Sun and Earth here), showing the five Lagrange points. ... A Trojan moon is a natural satellite of a planet occupying the L4 or L5 equilateral Lagrangian points of a primary-moon system. ... Image of the Trojan asteroids in front of and behind Jupiter along its orbital path. ... For other uses, see Jupiter (disambiguation). ... Atmosphere none Telesto IPA: , Greek Τελεστώ) is a moon of Saturn. ... Atmosphere none Calypso (ka-lip-soe, Greek Καλυψώ) is a moon of Saturn. ... Not to be confused with the asteroid named 17 Thetis. ... Helene (hel-e-nee, Greek ‘Ελένη) is a moon of Saturn. ... Saturns moon Polydeuces Atmosphere none Polydeuces (pol-ee-dew-seez, IPA: , Greek Πολυδεύκης) is a very small natural satellite of Saturn that is co-orbital with Dione and librates around the trailing Lagrangian point (L5). ... Atmosphere none Dione (dye-oe-nee, Greek Διώνη) is a moon of Saturn discovered by Giovanni Cassini in 1684. ...


Asteroid satellites

Main article: asteroid moon

The discovery of 243 Ida's moon Dactyl in the early 1990s confirmed that some asteroids have moons; indeed, 87 Sylvia has two. Some, such as 90 Antiope, are double asteroids with two comparably sized components. 243 Ida and its moon Dactyl An asteroid moon is an asteroid that orbits another asteroid. ... NASA image of 243 Ida. ... 243 Ida (left) and Dacytl (right), as photographed by Galileo. ... For other uses, see Asteroid (disambiguation). ... 87 Sylvia (sil-vee-a) is one of the largest main belt asteroids. ... 90 Antiope (an-tye-a-pee) is an asteroid discovered on October 1, 1866 by Robert Luther. ...


Natural satellites of the Solar System

The largest natural satellites in the Solar System (those bigger than about 3000 km across) are Earth's moon, Jupiter's Galilean moons (Io, Europa, Ganymede, and Callisto), Saturn's moon Titan, and Neptune's captured moon Triton. For smaller moons see the articles on the appropriate planet. In addition to the moons of the various planets there are also over 80 known moons of the dwarf planets, asteroids and other small solar system bodies. Some studies estimate that up to 15% of all trans-Neptunian objects could have satellites. This article is about Earths moon. ... For other uses, see Jupiter (disambiguation). ... Jupiters 4 Galilean moons, in a composite image comparing their sizes and the size of Jupiter (Great Red Spot visible). ... Atmosphere Surface pressure: trace Composition: 90% sulfur dioxide Io (eye-oe, IPA: , Greek Ῑώ) is the innermost of the four Galilean moons of Jupiter and, with a diameter of 3,642 kilometers, is the fourth largest moon in the Solar System. ... Apparent magnitude: 5. ... This article is about the natural satellite of Jupiter. ... There is also an asteroid named 204 Kallisto. ... This article is about the planet. ... Titan (, from Ancient Greek Τῑτάν) or Saturn VI is the largest moon of Saturn and the only moon known to have a dense atmosphere. ... For other uses, see Neptune (disambiguation). ... Triton (trye-tÉ™n, IPA: , Greek Τρίτων), or Neptune I, is the planet Neptunes largest moon. ... Artists impression of Pluto (background) and Charon (foreground). ... For other uses, see Asteroid (disambiguation). ... It has been suggested that minor planet be merged into this article or section. ... A trans-Neptunian object (TNO) is any object in the solar system that orbits the sun at a greater distance on average than Neptune. ...


The following is a comparative table classifying the moons of the solar system by diameter. The column on the right includes some notable planets, dwarf planets, asteroids, and Trans-Neptunian Objects for comparison. It is normal for natural satellites to be named after mythological figures, (predominately Greek), however Uranus's moons are named after Shakespearean characters. The nineteen bodies massive enough to have achieved hydrostatic equilibrium are in bold. Those suspected but not proven to have achieved a hydrostatic equilibrium are italicized. For other uses, see Uranus (disambiguation). ... Hydrostatic equilibrium occurs when compression due to gravity is balanced by a pressure gradient which creates a pressure gradient force in the opposite direction. ...

Mean diameter
(km)
Satellites of planets Dwarf planet satellites Satellites of
SSSBs
Non-satellites
for comparison
Earth Mars Jupiter Saturn Uranus Neptune Pluto Eris
6000-7000 Mars
5000-6000 Ganymede Titan
4000-5000 Callisto Mercury
3000-4000 The Moon
(Luna)
Io
Europa
2000-3000 Triton Eris
Pluto
1500-2000 Rhea Titania
Oberon
(136472) 2005 FY9
90377 Sedna
1000-1500 Iapetus
Dione
Tethys
Umbriel
Ariel
Charon (136108) 2003 EL61
90482 Orcus
50000 Quaoar
500-1000 Enceladus Ceres
20000 Varuna
28978 Ixion
2 Pallas4 Vesta
many more TNOs
250-500 Mimas
Hyperion
Miranda Proteus
Nereid
Dysnomia S/2005 (2003 EL61) 1
S/2005 (79360) 1
10 Hygiea
511 Davida
704 Interamnia
and many others
100-250 Amalthea
Himalia
Thebe
Phoebe
Janus
Epimetheus
Sycorax
Puck
Portia
Larissa
Galatea
Despina
S/2005 (2003 EL61) 2
many more TNOs
many
50-100 Elara
Pasiphaë
Prometheus
Pandora
Caliban
Juliet
Belinda
Cressida
Rosalind
Desdemona
Bianca
Thalassa
Halimede
Neso
Naiad
Nix[6]
Hydra[6]
Menoetius[7]
S/2000 (90) 1
many more TNOs
many
10-50 Phobos Carme
Metis
Sinope
Lysithea
Ananke
Leda
Adrastea
Siarnaq
Helene
Albiorix
Atlas
Pan
Telesto
Paaliaq
Calypso
Ymir
Kiviuq
Tarvos
Ijiraq
Erriapus
Ophelia
Cordelia
Setebos
Prospero
Perdita
Mab
Stephano
Cupid
Francisco
Ferdinand
Margaret
Trinculo
Sao
Laomedeia
Psamathe
Linus[8]
S/2000 (762) 1
S/2002 (121) 1
Romulus[9]
Petit-Prince[10]
S/2003 (283) 1
S/2004 (1313) 1
and many TNOs
many
less than 10 2006 RH120 (temporary) Deimos at least 47 at least 21 many many


A Small Solar System Body (SSSB) is a term defined in 2006 by the International Astronomical Union to describe objects in the Solar System that are neither planets nor dwarf planets: [1] This encompasses: all minor planets apart from the dwarf planets, : the classical asteroids, (except for 1 Ceres, the... Mars is the fourth planet from the Sun in the solar system, named after the Roman god of war (the counterpart of the Greek Ares), on account of its blood red color as viewed in the night sky. ... This article is about the natural satellite of Jupiter. ... Titan (, from Ancient Greek Τῑτάν) or Saturn VI is the largest moon of Saturn and the only moon known to have a dense atmosphere. ... There is also an asteroid named 204 Kallisto. ... This article is about the planet. ... This article is about Earths moon. ... Atmosphere Surface pressure: trace Composition: 90% sulfur dioxide Io (eye-oe, IPA: , Greek Ῑώ) is the innermost of the four Galilean moons of Jupiter and, with a diameter of 3,642 kilometers, is the fourth largest moon in the Solar System. ... Apparent magnitude: 5. ... Triton (trye-tÉ™n, IPA: , Greek Τρίτων), or Neptune I, is the planet Neptunes largest moon. ... Absolute magnitude: −1. ... For other uses, see Pluto (disambiguation). ... Atmosphere none Rhea (ree-a, Greek ‘Ρέα) is the second largest moon of Saturn and was discovered in 1672 by Giovanni Domenico Cassini. ... Not to be confused with the Saturnian moon Titan or the asteroid 593 Titania. ... Atmospheric pressure 0 kPa Oberon (oe-bur-on) is the outermost of the major moons of the planet Uranus. ... (also written (136472) 2005 FY9) is a very large Kuiper belt object, and one of the two largest among the population in the classical KBO orbits. ... you are abunch of bull | bgcolour=#FFFFC0 | name=90377 Sedna | image= | caption= Sedna is located in the center of the green circle | discovery=yes | discoverer=M. Brown, C. Trujillo, D. Rabinowitz | discovered=November 14, 2003 | mp_name=90377 Sedna | alt_names= | mp_category=Trans-Neptunian object | epoch=September 26, 1990 (JD 2448160. ... Iapetus (eye-ap-É™-tÉ™s, IPA , Greek Ιαπετός) is the third-largest moon of Saturn, discovered by Giovanni Domenico Cassini in 1671. ... Atmosphere none Dione (dye-oe-nee, Greek Διώνη) is a moon of Saturn discovered by Giovanni Cassini in 1684. ... Not to be confused with the asteroid named 17 Thetis. ... Atmospheric pressure 0 kPa Umbriel (um-bree-É™l, IPA ) is a moon of Uranus discovered on 1851-10-24 by William Lassell. ... Atmospheric pressure 0 kPa Ariel (air-ee-É™l, IPA ) is a moon of Uranus discovered on 24 October 1851 by William Lassell. ... Charon (shair-É™n or kair-É™n (key), IPA , Greek Χάρων), discovered in 1978, is, depending on the definition employed, either the largest moon of Pluto or one member of a double dwarf planet with Pluto being the other member. ... (also written (136108) 2003 EL61), nicknamed Easter Bunny, is a large Kuiper belt object, roughly one-third the mass of Pluto, discovered by J. L. Ortiz et al. ... 90482 Orcus (originally known by the provisional designation 2004 DW) is a Kuiper Belt object (KBO) that was discovered by Michael Brown of Caltech, Chad Trujillo of the Gemini Observatory, and David Rabinowitz of Yale University. ... Quaoar redirects here. ... Apparent magnitude 11. ... Spectral type: G[8] Absolute magnitude: 3. ... 20000 Varuna (VAR oo na) is a large classical Kuiper Belt object (KBO). ... 28978 Ixion (IPA pronunciation: , Wiktionary:Ixion) is a Kuiper belt object discovered on May 22, 2001. ... 2 Pallas (pal-us, Greek Παλλάς) was the first asteroid discovered after 1 Ceres. ... 4 Vesta (ves-ta) is the second most massive asteroid in the asteroid belt, with a mean diameter of about 530 km and an estimated mass 12% the mass of the entire asteroid belt. ... A trans-Neptunian object (TNO) is any object in the solar system that orbits the sun at a greater distance on average than Neptune. ... Mimas (mee-mÉ™s or mye-mÉ™s, IPA: , Greek Μίμᾱς, rarely Μίμανς) is a moon of Saturn that was discovered in 1789 by William Herschel. ... Hyperion (IPA: , Greek Ὑπερίων) is a moon of Saturn discovered by William Cranch Bond, George Phillips Bond and William Lassell in 1848. ... Miranda (IPA: ) is the smallest and innermost of Uranus five major moons. ... Atmospheric pressure 0 kPa Proteus (proe-tee-us, Greek Πρωτέας) is one of Neptunes moons. ... Nereid (IPA: , IPA: , Greek Νηρηίδα), or Neptune II, is a moon of Neptune. ... Dysnomia (officially designated (136199) Eris I Dysnomia) is a moon of the dwarf planet Eris. ... (also written (136108) 2003 EL61), nicknamed Easter Bunny, is a large Kuiper belt object, roughly one-third the mass of Pluto, discovered by J. L. Ortiz et al. ... (79360) 1997 CS29, also written as 1997 CS29, is a cubewano. ... 10 Hygiea (hye-jee-a or hi-jee-a) is the fourth largest Main belt asteroid with a diameter of 407 km. ... 511 Davida is a main belt asteroid. ... 704 Interamnia (IN ter AM nia) is a very large asteroid with a diameter of 350 kilometres. ... Apparent magnitude: 14. ... Atmospheric pressure 0 kPa Himalia (hye-mal-ee-a, also hi-mahl-ee-a, IPA , ; Greek ‘Ιμαλíα) is a moon of Jupiter. ... Atmospheric pressure 0 kPa Thebe (thee-bee, IPA ; Greek Θήβη) is the fourth of Jupiters known moons by distance from the planet. ... For other meanings see Phoebe. ... Janus (jay-nus, IPA: , Greek Ιανός) is an inner satellite of Saturn. ... Epimetheus (ep-i-mee-thee-us, Greek Επιμηθεύς) is a moon of Saturn. ... Atmospheric pressure 0 kPa Sycorax (sik-or-aks) is a moon of Uranus. ... Atmospheric pressure 0 kPa Puck (puk) is a moon of Uranus. ... Atmospheric pressure 0 kPa Portia (por-sha) is a moon of Uranus. ... A simulated view of Larissa orbiting Neptune Larissa (la-ris-a, Greek Λάρῑσα) is the fifth of Neptunes known moons. ... A simulated view of Galatea orbiting Neptune Galatea (gal-a-tee-a, Greek Γαλατεία) is the fourth known moon of Neptune, named after Galatea, one of the Nereids of Greek legend. ... A simulated view of Despina orbiting Neptune Despina (des-pee-na or des-pye-na; Latin DespÅ“na from Greek Δεσποίνη) is the third known moon of Neptune. ... (also written (136108) 2003 EL61), nicknamed Easter Bunny, is a large Kuiper belt object, roughly one-third the mass of Pluto, discovered by J. L. Ortiz et al. ... A trans-Neptunian object (TNO) is any object in the solar system that orbits the sun at a greater distance on average than Neptune. ... Atmospheric pressure 0 kPa Elara (ee-lur-a or ee-lair-a, IPA or , Greek Ελάρη) is a moon of Jupiter. ... Pasiphaë (IPA: , pa-sif-a-ee, Greek Πασιφάη) is a moon of Jupiter. ... Prometheus (proe-mee-thee-us, Greek Προμηθέας) is a moon of Saturn. ... Pandora (pan-dor-a, Greek Πανδώρα) is a moon of Saturn. ... Atmosphere none Caliban (kal-i-ban or kal-a-bun) is a moon of Uranus, named after the monster character in William Shakespeares play The Tempest. ... Atmospheric pressure 0 kPa Juliet (jew-lee-et ) is a moon of Uranus. ... Atmospheric pressure 0 kPa Belinda (be-lin-da) is a moon of Uranus. ... Atmospheric pressure 0 kPa Cressida (kres-i-da) is a moon of Uranus. ... Atmospheric pressure 0 kPa Rosalind (roz-a-lind) is a moon of Uranus. ... Atmospheric pressure 0 kPa Desdemona (dez-di-moe-na) is a moon of Uranus. ... Bianca orbiting Uranus There is also an asteroid called 218 Bianca. ... A simulated view of Thalassa orbiting Neptune. ... Halimede is a retrograde irregular satellite of Neptune. ... Neso, also known as Neptune XIII, is the outermost irregular natural satellite of Neptune. ... A simulated view of Naiad orbiting Neptune with The Sun in the distance. ... Nix (formerly known as S/2005 P 2), is a natural satellite of Pluto. ... Hydra (formerly known as S/2005 P 1) is a natural satellite of Pluto. ... 617 Patroclus is the second Jovian Trojan asteroid to be discovered. ... 90 Antiope (an-tye-a-pee) is an asteroid discovered on October 1, 1866 by Robert Luther. ... A trans-Neptunian object (TNO) is any object in the solar system that orbits the sun at a greater distance on average than Neptune. ... Phobos (IPA: or [ˈfoÊŠ.bÉ™s]) (systematic designation: ) is the larger and closer of Mars two moons (the other being Deimos). ... Atmospheric pressure 0 kPa Carme (IPA: , kar-mee, Greek Κάρμη) is one of Jupiters moons. ... Atmospheric pressure 0 kPa Metis (mee-tÉ™s, IPA: , Greek Μήτις), or Jupiter XVI, is the innermost member of the Jupiters small inner moons and thus Jupiters innermost moon. ... Atmospheric pressure 0 kPa Sinope (IPA: , si-noe-pee, Greek Σινώπη) is a moon of Jupiter discovered by Seth Barnes Nicholson at Lick Observatory in 1914, and is named after Sinope of Greek mythology. ... Lysithea (lye-sith-ee-É™ or lÉ™-sith-ee-É™, IPA: ; Greek Λυσιθέα) is a prograde irregular satellite of Jupiter. ... Atmospheric pressure 0 kPa Ananke (a-nang-kee, IPA ; Greek Ανάγκη) is one of Jupiters moons. ... Atmospheric pressure 0 kPa For the asteroid, see 38 Leda Leda (lee-dÉ™, IPA: ; Greek Λήδα), or Jupiter XIII, is a prograde irregular satellite of Jupiter that was discovered by Charles T. Kowal at the Mount Palomar Observatory on September 14, 1974, right after three nights worth of photographic plates had... Atmospheric pressure 0 kPa Adrastea (IPA: , ad-ra-stee-a, Greek Αδράστεια) is the second of Jupiters known moons (counting outward from the planet). ... Siarnaq (see-ar-naak) (Saturn XXIX) is a natural satellite of Saturn. ... Helene (hel-e-nee, Greek ‘Ελένη) is a moon of Saturn. ... Albiorix (al-bee-or-iks) is a natural satellite of Saturn. ... Atmospheric pressure 0 kPa Atlas (at-lus, Greek Άτλας) is a moon of Saturn. ... Atmosphere none Pan (pan, Greek Πάν) is a moon of Saturn, named after the god Pan. ... Atmosphere none Telesto IPA: , Greek Τελεστώ) is a moon of Saturn. ... Paaliaq (paw-lee-aak) is a natural satellite of Saturn. ... Atmosphere none Calypso (ka-lip-soe, Greek Καλυψώ) is a moon of Saturn. ... Ymir (ee-mur) (Saturn XIX) is a natural satellite of Saturn. ... Kiviuq (kee-vee-oek or kiv-ee-uk) is a natural satellite of Saturn. ... Tarvos (tar-vus) (Saturn XXI) is a natural satellite of Saturn. ... Ijiraq (ee-ye-raak or ee-ji-raak) is a natural satellite of Saturn. ... Atmospheric pressure 0 kPa Ophelia (o-fee-lee-a) is a moon of Uranus. ... Atmospheric pressure 0 kPa Cordelia (kor-dee-lee-a) is the innermost moon of Uranus. ... Atmospheric pressure 0 kPa Setebos (set-e-bus) is Uranus outermost named moon, surpassed only by S/2001 U 2. ... Atmospheric pressure 0 kPa Prospero (pros-pur-oe) is a relatively small natural satellite of the planet Uranus named after the sorcerer in William Shakespeares play The Tempest. ... Atmospheric pressure 0 kPa Perdita (pur-di-ta, IPA ) is a moon of Uranus. ... Atmospheric pressure 0 kPa Mab (mab, IPA [mæb]) is a natural satellite of Uranus. ... Atmospheric pressure 0 kPa Stephano (stef-a-noe or ste-faa-noe) is a natural satellite of Uranus. ... Atmospheric pressure 0 kPa Cupid (kew-pid, IPA: ) is an inner satellite of Uranus. ... Atmospheric pressure 0 kPa Francisco (fran-sis-koe, IPA ) is a natural satellite of Uranus. ... Atmospheric pressure 0 kPa Ferdinand (fur-di-nand, IPA ) is a natural satellite of Uranus. ... Atmospheric pressure 0 kPa Margaret (mar-grit)is a natural satellite of Uranus. ... Atmospheric pressure 0 kPa Trinculo (tring-kew-loe) is a natural satellite of Uranus. ... Sao is a prograde irregular satellite of Neptune. ... Laomedeia, or Neptune XII, is a prograde irregular satellite of Neptune. ... Psamathe (sam-a-thee, Greek Ψαμαθεια, Latin PsamathÄ“) is an irregular natural satellite of Neptune. ... (22) Kalliope I Linus is an asteroid moon that orbits the large M-type asteroid 22 Kalliope. ... 762 Pulcova is a main belt asteroid. ... 121 Hermione is a very large and dark main belt asteroid. ... Sylvia and Romulus Romulus is the outer and larger moon of the main belt asteroid 87 Sylvia, not to be confused with the directly Sun-orbiting asteroid 10386 Romulus. ... Petit-Prince orbiting Eugenia (45) Eugenia I Petit-Prince is an asteroid moon that orbits the larger asteroid 45 Eugenia. ... 283 Emma is a very large main belt asteroid. ... 1313 Berna is an asteroid orbiting the Sun. ... A trans-Neptunian object (TNO) is any object in the solar system that orbits the sun at a greater distance on average than Neptune. ... Deimos (IPA or ; Greek Δείμος: Dread), is the smaller and outermost of Mars’ two moons, named after Deimos from Greek Mythology. ... Jupiters outer moons and their highly inclined orbits. ... The Saturnian system (photographic montage) Saturn has 60 confirmed natural satellites, plus three hypothetical moons. ...


Terminology

The first known natural satellite was the Moon (luna in Latin). Until the discovery of the Galilean satellites in 1610, however, there was no opportunity for referring to such objects as a class. Galileo chose to refer to his discoveries as Planetæ ("planets"), but later discoverers chose other terms to distinguish them from the objects they orbited. This article is about Earths moon. ... For other uses, see Latins and Latin (disambiguation). ... Jupiters 4 Galilean moons, in a composite image comparing their sizes and the size of Jupiter (Great Red Spot visible). ... Galileo redirects here. ... This article is about the astronomical term. ...


Christiaan Huygens, the discoverer of Titan, was the first to use the term moon for such objects, calling Titan Luna Saturni or Luna Saturnia – "Saturn's moon" or "The Saturnian moon", because it stood in the same relation to Saturn as the Moon did to the Earth. Christiaan Huygens (pronounced in English (IPA): ; in Dutch: ) (April 14, 1629 – July 8, 1698), was a Dutch mathematician, astronomer and physicist; born in The Hague as the son of Constantijn Huygens. ... Titan (, from Ancient Greek Τῑτάν) or Saturn VI is the largest moon of Saturn and the only moon known to have a dense atmosphere. ... This article is about the planet. ... This article is about Earth as a planet. ...


As additional moons of Saturn were discovered, however, this term was abandoned. Giovanni Domenico Cassini sometimes referred to his discoveries as planètes in French, but more often as satellites, using a term derived from the Latin satelles, meaning "guard", "attendant", or "companion", because the satellites accompanied their primary planet in their journey through the heavens. Giovanni Domenico (Jean-Dominique) Cassini Portrait Giovanni Domenico Cassini (June 8, 1625–September 14, 1712) was an Italian astronomer, engineer, and astrologer. ...


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. The terms man-made satellite or artificial moon were very quickly abandoned in favor of the simpler satellite, and as a consequence, the term has come to be linked primarily with artificial objects flown in space – including, sometimes, even those which are not in orbit around a planet. Sputnik 1 The Sputnik program was a series of unmanned space missions launched by the Soviet Union in the late 1950s to demonstrate the viability of artificial satellites. ...


As a consequence 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 satellite, even in scientific articles. When it is necessary to avoid both the ambiguity of confusion with the Earth's moon on the one hand, and artificial satellites on the other, the term natural satellite (using "natural" in a sense opposed to "artificial") is used.


The definition of a moon

Comparison of Earth and the Moon
Comparison of Earth and the Moon
Comparison of Pluto and Charon
Comparison of Jupiter's Great Red Spot and Jupiter's four largest moons. Compared to Earth/Luna and Pluto/Charon, there is a much greater difference in mass.
Comparison of Jupiter's Great Red Spot and Jupiter's four largest moons. Compared to Earth/Luna and Pluto/Charon, there is a much greater difference in mass.

There is no established lower limit on what should be considered a moon. Every body with an identified orbit, some as small as a kilometer across, has been identified as a moon, though objects a tenth that size within Saturn's rings, which have not been directly observed, have been called moonlets. Small asteroid moons, such as Dactyl, have also been called moonlets. Image File history File links Moon_Earth_Comparison. ... Image File history File links Moon_Earth_Comparison. ... This article is about Earth as a planet. ... This article is about Earths moon. ... Image File history File links Plutoncharon1. ... Image File history File links Plutoncharon1. ... For other uses, see Pluto (disambiguation). ... Charon (shair-ən or kair-ən (key), IPA , Greek Χάρων), discovered in 1978, is, depending on the definition employed, either the largest moon of Pluto or one member of a double dwarf planet with Pluto being the other member. ... Image File history File links Jupiter. ... Image File history File links Jupiter. ... For other uses, see Jupiter (disambiguation). ... A false-color image of the Great Red Spot of Jupiter from Voyager 1. ... Jupiters 4 Galilean moons, in a composite image comparing their sizes and the size of Jupiter (Great Red Spot visible). ... For other uses, see Mass (disambiguation). ... The tiny moonlet Dactyl (right) in orbit around the asteroid 243 Ida. ... 243 Ida (left) and Dactyl (right), as photographed by the Galileo spacecraft. ...


The upper limit is also vague. When the masses of two orbiting bodies are similar enough that one cannot be said to orbit the other, they are described as a double body rather than primary and satellite. Asteroids such as 90 Antiope are considered double asteroids, but they have not forced a clear definition as to what constitutes a moon. Some authors consider the Pluto-Charon system to be a double (dwarf) planet. The most common 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, as it relies on distance as well as relative mass. Pluto and Charon are sometimes informally considered to be a double (dwarf) planet. ... For other uses, see Asteroid (disambiguation). ... 90 Antiope (an-tye-a-pee) is an asteroid discovered on October 1, 1866 by Robert Luther. ... The barycenter (from the Greek βαρύκεντρον) is the center of mass of two or more bodies which are orbiting each other, and is the point around which both of them orbit. ...


The smallest extra-Solar objects so far found to have satellites are brown dwarfs and sub-brown dwarfs; their satellites are considered planets rather than moons.


See also

  • Co-orbital moon
  • Extrasolar moon
  • Inner moon
  • Irregular moon
  • List of moons
  • List of moons by diameter
  • Naming of moons
  • Quasi-satellite
  • Timeline of discovery of Solar System planets and their moons
  • Trojan moon

Co-orbital moons are natural satellites that orbit at the same distance from their parent planet as another satellite, or at a similar distance. ... The term Extrasolar moon refers to a natural (non-man-made) satellite that orbits an extrasolar planet or other extrasolar body larger than itself. ... This diagram shows the orbits of Saturns irregular satellites surrounding the planet like a swarm. ... Diagram of generic quasi-satellite orbit A quasi-satellite is an object similar to a planet or satellite of the Sun, however its orbit encompasses its planet and the planets star. ... A Trojan moon is a natural satellite of a planet occupying the L4 or L5 equilateral Lagrangian points of a primary-moon system. ...

Moons of planets

This article is about Earths moon. ... The relative sizes of and distance between Mars, Phobos, and Deimos, to scale : Phobos (top) and Deimos (bottom). ... Jupiters 4 Galilean moons, in a composite image comparing their sizes and the size of Jupiter (Great Red Spot visible). ... The Saturnian system (photographic montage) Moons of Saturn (photographic montage) Saturn has 60 confirmed natural satellites, plus three hypothetical moons. ... Uranus has twenty-seven known moons. ... Neptune (top) and Triton (bottom), 3 days after the Voyager 2 flyby. ...

Moons of dwarf planets and small Solar System bodies

243 Ida and its moon Dactyl An asteroid moon is an asteroid that orbits another asteroid. ... Hubble image of the Plutonian system Pluto has three known moons. ... Dysnomia (officially designated (136199) Eris I Dysnomia) is a moon of the dwarf planet Eris. ...

Notes and references

  1. ^ List of natural satellites orbiting the planets.
  2. ^ R. Canup and E. Asphaug (2001). "Origin of the Moon in a giant impact near the end of the Earth's formation". Nature 412: 708-712. 
  3. ^ S. Stern, H. Weaver, A. Steffl, M. Mutchler, W. Merline, M. Buie, E. Young, L. Young, and J. Spencer (2006). "A giant impact origin for Pluto's small moons and satellite multiplicity in the Kuiper belt". Nature 439: 946-949. 
  4. ^ The Dust Halo of Saturn's Largest Icy Moon, Rhea -- Jones et al. 319 (5868): 1380 -- Science. Retrieved on 2008-03-06.
  5. ^ Saturn satellite reveals first moon rings - 06 March 2008 - New Scientist. Retrieved on 2008-03-06.
  6. ^ a b Diameters of the new Plutonian satellites are still very poorly known, but they are estimated to lie between 44 and 130 km.
  7. ^ (617) Patroclus I Menoetius
  8. ^ (22) Kalliope I Linus
  9. ^ (87) Sylvia I Romulus
  10. ^ (45) Eugenia I Petit-Prince

2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 65th day of the year (66th in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 65th day of the year (66th in leap years) in the Gregorian calendar. ...

External links

Jupiter's moons

Saturn's moons

All moons

In astronomy, an inner satellite is a natural satellite following a prograde, low inclination orbit inwards of the large satellites of the parent planet. ... In astronomy, an irregular satellite is a natural satellite following a distant, inclined, often retrograde orbit and believed to be captured as opposed to a regular satellite, formed in situ. ... A Trojan moon is a natural satellite of a planet occupying the L4 or L5 equilateral Lagrangian points of a primary-moon system. ... This is a list of natural satellites in the solar system: Mercury: none Venus: none Earth: Moon Mars: Phobos Deimos Jupiter: see Jupiters natural satellites Saturn: see Saturns natural satellites Uranus: see Uranus natural satellites Neptune: see Neptunes natural satellites Pluto: Charon In addition, various asteroids are... This is a list of natural satellites in the solar system, ordered from largest to smallest by average diameter. ... This timeline of discovery of Solar System planets and their natural satellites charts the progress of the discovery of new bodies over history. ... The naming of natural satellites has been the responsibility of the IAUs committee for Planetary System Nomenclature since 1973. ... This article is about the Solar System. ... Sol redirects here. ... This article is about the planet. ... For other uses, see Venus (disambiguation). ... This article is about Earth as a planet. ... Adjectives: Martian Atmosphere Surface pressure: 0. ... Spectral type: G[8] Absolute magnitude: 3. ... For other uses, see Jupiter (disambiguation). ... This article is about the planet. ... For other uses, see Uranus (disambiguation). ... For other uses, see Neptune (disambiguation). ... For other uses, see Pluto (disambiguation). ... Absolute magnitude: −1. ... This article is about the astronomical term. ... Artists impression of Pluto (background) and Charon (foreground). ... This article is about Earths moon. ... The relative sizes of and distance between Mars, Phobos, and Deimos, to scale : Phobos (top) and Deimos (bottom). ... Jupiters 4 Galilean moons, in a composite image comparing their sizes and the size of Jupiter (Great Red Spot visible). ... The Saturnian system (photographic montage) Moons of Saturn (photographic montage) Saturn has 60 confirmed natural satellites, plus three hypothetical moons. ... Uranus has twenty-seven known moons. ... Neptune (top) and Triton (bottom), 3 days after the Voyager 2 flyby. ... Hubble image of the Plutonian system Pluto has three known moons. ... Dysnomia (officially designated (136199) Eris I Dysnomia) is a moon of the dwarf planet Eris. ... A Small Solar System Body (SSSB) is a term defined in 2006 by the International Astronomical Union to describe objects in the Solar System that are neither planets nor dwarf planets: [1] This encompasses: all minor planets apart from the dwarf planets, : the classical asteroids, (except for 1 Ceres, the... Meteor redirects here. ... For other uses, see Asteroid (disambiguation). ... 243 Ida and its moon Dactyl An asteroid moon is an asteroid that orbits another asteroid. ... For other uses, see Asteroid (disambiguation). ... The centaurs are a class of icy planetoids that orbit the Sun between Jupiter and Neptune, named after the mythical race of centaurs. ... A trans-Neptunian object (TNO) is any object in the solar system that orbits the sun at a greater distance on average than Neptune. ... The Kuiper belt, derived from data from the Minor Planet Center. ... Eris, the largest known scattered disc object (center), and its moon Dysnomia (left of center). ... Comet Hale-Bopp Comet West For other uses, see Comet (disambiguation). ... Artists rendering of the Oort cloud and the Kuiper Belt. ... Astronomical objects are significant physical entities, associations or structures which current science has confirmed to exist in space. ... Below is a list of solar system objects with diameter >500km: The Sun, a spectral class G2 star Mercury Venus Earth Moon Mars Jupiter Io Europa Ganymede Callisto complete list of Jupiters natural satellites Saturn Tethys Dione Rhea Titan Iapetus complete list of Saturns natural satellites Uranus Ariel... It has been suggested that Planetary-size comparison be merged into this article or section. ... This is a list of solar system objects by mass, in decreasing order. ...

  Results from FactBites:
 
natural satellite — FactMonster.com (311 words)
Ariel, in astronomy - Ariel Ariel, in astronomy, one of the moons, or natural satellites, of Uranus.
Amalthea - Amalthea Amalthea, in astronomy, one of the 39 known moons, or natural satellites, of Jupiter.
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Natural Satellite - MSN Encarta (415 words)
The motion of most of the solar system's natural satellites about their planets is direct: west to east, in the same direction as the rotation of their planets.
Several small satellites of the large outer planets, however, revolve in the retrograde direction: east to west, opposite the direction of the rotation of their planets.
These retrograde satellites tend to orbit far from their primaries and were probably captured by the planets' gravitational fields some time after the formation of the solar system.
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