Natural satellites are objects orbiting planets or other bodies larger than itself and which is not man-ready-made. Natural satellites are often called moons. Technically, the term could also refer to a planet orbiting a star, or even to a star orbiting a Galactic centerfield, but these uses are rare. Instead, the term is normally used to nam non-artificial satellites of planets, dwarf planets, or minor planets.
Moons of the Solar System scaled to Earth's Lunar month.
On that point are 240 known moons within the Star System, including 162 orbiting the planets, 4 orbiting dwarf planets, and dozens more orbiting small solar system bodies. Other stars and their planets besides have natural satellites.
The large gas giants sustain extensive systems of moons, including half a 12 comparable to in size up to Earth's Moon. Of the inner planets, Hg and Venus have no moons at all; World has one broad lunar month ("the Moon" or "Luna"); and Mars has two tiny moons, Phobos and Deimos. Among the gnome planets, Ceres has atomic number 102 moons (though many a objects in the asteroid belt manage), Eris has one, Dysnomia, and Hades has three known satellites, Nix, Hydra, and a queen-size companion called Charon. Charon is as wel unusual in that it does not celestial orbit Pluto, but rather both bodies orbit a barycenter in empty space, making Pluto-Charon a binary system.
Origin of unaffected satellites.
Moons orbiting comparatively close to the planet along prograde orbits (regular satellites) are believed to have been formed out of the same collapsing area of protoplanetary disk that gave rise to its primary. Most Irregular satellites (orbiting on distant, inclined, eccentric often retrograde orbits) are thought to be captured asteroids perhaps further fragmented past collisions. Many extraordinary scenarios exist, including line of descent in a break-up of the planet. For lesson, the Earth's Moon is theorized to have formed from corporal blasted into electron orbit by a large bear on. In contrast, the large Neptunian satellite Triton is known to be a captured Trans-Neptunian targe because of its retrograde orbital cavity, even though IT orbits rather close to Neptune.
Orbital characteristics of natural satellites.
Most regular moons in the solar system are tidally locked to their primaries, meaning that ane side of the moon is always turned toward the planet. Exceptions include Saturn's moon Hyperion, which rotates chaotically because of a variety of external influences.
In contrast, the outer moons of the swash giants (randomized satellites) are too long off to get on 'bolted'. For example, Jupiter's Sun Myung Moon Himalia, Saturn's moon Phoebe and Neptune's Nereid have rotary motion period in the range of 10 hours compared with their bodily cavity periods of hundreds of days.
Satellites of satellites.
No "moons of moons" (natural satellites that orbit the natural satelite of another body) are known. It is uncertain whether so much objects can be stable in the long terminus. In most cases, the tidal personal effects of their primaries make such a system seismic; the gravity from other nigh objects (near notably the primary) would perturb the orbit of the moon's moon until it broke away or impacted its of import. In essence, a thirdhand satellite could exist in a primary satellite's Hill sphere, outside of which IT would beryllium lost because of the greater gravitational pull of the planet (or other physical object) that the primary satellite orbits. For example, the Moon orbits the Earthly concern because the Moonlight is 370,000 km from Earth, well within Dry land's J. J. Hill sphere, which has a radius of 1.5 million km (0.01 AU or 235 Earth radii). If a Moon-sized object were to orbit the Earth outside its Hill sphere, it would soon be captured aside the Sun and go a Dwarf satellite in a most-Earth orbit.
City satellites.
However, two moons are known have small companions in their L4 and L5 Lagrangian points of their orbits, near threescore degrees ahead of and behind their positions. These companions are called Trojan moons, because their positions are comparable the positions of the Trojan asteroids relative to Jove. They are Telesto and Fairy-slipper, the leading and following companions respectively of Tethys; and Helene and Polydeuces, the leading and next companions of Dione.
Asteroid satellites.
The Recent epoch discovery of 243 Ida's moon Dactyl confirms that some asteroids also birth moons. Approximately, like 90 Antiope, are double asteroids with two equate-sized components. The asteroid 87 Sylvia has two moons. See Star-shaped moon for foster information.
Moons of the Star scheme.
The largest moons in the solar system (those bigger than about 3000 kilometer across) are Earth's Moon, Jove's Stargazer moons (Io, Europa, Ganymede, and Callisto), Saturn's moon Titan, and Neptune's captured moon Triton. For smaller moons see the articles connected the expedient planet. In addition to the moons of the various planets there are too over 80 better-known moons of the dwarf planets, asteroids and other small star system bodies. Some studies reckon that improving to 15% of all trans-Neptunian objects could have satellites.
The following is a relation put over classifying the moons of the solar organization by diameter. The column on the right includes both notable planets, dwarf planets, asteroids, and Trans-Neptunian Objects for comparison.
| Mean diameter (km) | Satellites of planets | Dwarf planet satellites | Satellites of SSSBs | Not-satellites for comparison | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Earth | Mars | Jupiter | Saturn | Uranus | Neptune | Pluto | Eris | |||
| 6000-7000 | Mars | |||||||||
| 5000-6000 | Ganymede | Titan | ||||||||
| 4000-5000 | Callisto | Mercury | ||||||||
| 3000-4000 | Moon | Io Europa | ||||||||
| 2000-3000 | Triton | Eris Pluto | ||||||||
| 1000-2000 | Rhea Iapetus Dione Tethys | Titania Oberon Umbriel Ariel | Charon | (136472) 2005 FY9 (136108) 2003 EL61 90377 Sedna 90482 Orcus 50000 Quaoar | ||||||
| 500-1000 | Enceladus | Ceres 20000 Varuna 28978 Ixion 2 Pallas, 4 Vesta numerous 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 Pasipha� | Prometheus Pandora | Caliban Juliet Belinda Cressida Rosalind Desdemona Bianca | Thalassa S/2002 N 1 S/2002 N 4 Water nymph | Nix Hydra | Menoetius S/2000 (90) 1 some more TNOs | many | |||
| 10-50 | Phobos Deimos | Carme Metis Sinope Lysithea Ananke Leda Adrastea | Siarnaq Helene Albiorix Atlas Pan Telesto Paaliaq Fairy-slipper Ymir Kiviuq Tarvos Ijiraq Erriapo | Ophelia Cordelia Setebos Prospero Perdita Mab Stephano Cupid Francisco Ferdinand Margaret Trinculo | S/2002 N 2 S/2002 N 3 Psamathe | Linus S/2000 (762) 1 S/2002 (121) 1 Romulus Petit-Prince S/2003 (283) 1 S/2004 (1313) 1 and many TNOs | many | |||
| less than 10 | at least 47 | at any rate 21 | many | many | ||||||
Terminology of lifelike satellites.
The first known natural outer was the Moon (luna in Italic). Until the discovery of the Galilean moons in 1610, however, there was no opportunity for referring to so much objects as a form. Galileo chose to bring up to his discoveries as Planet� ("planets"), only later discoverers chose other terms to distinguish them from the objects they orbited.
Christiaan Christian Huygens, the discoverer of Titan, was the first to consumption the term moon for much 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.
As additional moons of Saturn were discovered, however, this term was abandoned. Giovanni Domenico Cassini sometimes referred to his discoveries as plan�tes in French, but more often as satellites, using a term derivable from the Latin satelles, meaning "guard", "accompaniment", or "companion", because the satellites accompanied their primary planet in their journey through the heavens.
The term satellite thus became the normal combined for referring to an object orbiting a planet, as it avoided the ambiguity of "moonshine". In 1957, all the same, the launching of the dummy object Sputnik created a need for new nomenclature. The terms unreal satellite operating room artificial moon were very speedily abandoned in favor of of the simpler satellite, and as a consequence, the terminal figure has follow to be linked chiefly with cardboard objects flown in space - including, sometimes, even those which are not in orbit approximately a satellite.
As a consequence of this shift in meaning, the term Sun Myung Moon, which had continuing to make up used in a generic sense in whole kit and boodle of popular science and in fable, has regained reputability and is now used interchangeably with satellite, even in scientific articles. When it is necessary to avoid both the ambiguity of discombobulation with the Earth's Moon on the one hand, and artificial satellites on the unusual, the term natural outer (using "natural" in a way opposed to "artificial") is used.
The definition of a moon.
Comparison of Earth and Luna (The Moon).
Equivalence of Pluto and Charon.
Comparison of Jupiter's Enceinte Red Spot and Jupiter's 4 largest moons. Compared to Earth/Luna and Pluto/Charon there is a much greater difference in mass.
There has been some debate virtually the precise definition of a moon. This debate has been caused by the presence of orbital systems where the difference in plenty 'tween the bigger organic structure and its satellite, are not arsenic pronounced as in median systems (a commonly accepted defining point is where the satellite is bigger than 1/40th the mass of the larger dead body) . Two examples let in the Pluto-Charon system, and the Earth-Luna System. The presence of these systems has caused a debate astir where to exactly draw a line 'tween a double body system, and a main body-artificial satellite arrangement, the most commonly agreed upon definition is whether the barycentre is below the coat of the larger physical structure, though this is non formalized. Another definition is whether the Sun or the larger body in the system has the most attractive force influence finished the satellite dubious. At the other end of the spectrum in that respect are many ice/rock clumps that form the ring systems on the Star System's gas giants and there is nary set dot to delimitate when one of these clumps is large enough to be classified as a moon, though the term "moonlet" may glucinium sometimes old to refer to extremely limited objects in orbit around a larger body, there is again no administrative body definition.
Natural satellites of planets and nanus planets.
- Land's unbleached satellite, see Moon.
- Mars' lifelike satellites.
- Jupiter's natural satellites.
- Saturn's natural satellites.
- Uranus' natural satellites.
- Neptune's natural satellites.
- Pluto's natural satellites.
- Eris' natural satellite, see Dysnomia.
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