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Natural satellite


The common noun moon (not capitalized) is used to mean any natural satellite of the other planets. There are, at least, 140 moons within Earth's solar system, and presumably many others orbiting the planets of other stars. Typically the larger gas giants have extensive systems of moons. Mercury and Venus have no moons at all, Earth has one large moon, Mars has two tiny moons, and Pluto a large companion called Charon (sometimes considered to be a double planet).

Contents

Origin

Most moons are assumed to have been formed out of the same collapsing region of protoplanetary disk that gave rise to its primary. However, there are many exceptions and variations to this standard model of moon formation that are known or theorized. Several moons are thought to be captured foreign objects, fragments of larger moons shattered by large impacts, or (in the case of Earth's Moon) a portion of the planet itself blasted into orbit by a large impact. As most moons are known only through a few distant observations through probes or telescopes, most theories about them are still uncertain.

Physical characteristics

Most moons in the solar system are tidally locked to their primaries; an exception is Saturn's moon Hyperion, which rotates chaotically due to a variety of external influences. No moons have moons of their own; the tidal effects of their primaries make orbits around them unstable. However, several moons have companions in their Lagrangian points (eg, Saturn's moons Tethys and Dione).

The recent discovery of Ida's moon Dactyl confirms that some asteroids also have moons. Some, like 90 Antiope, are double asteroids with two equal-sized components.

Moons of the Solar system

The largest moons 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 appropriate planets.

A comparative table classifying the moons of the solar system by diameter, also including a column for some notable asteroids, planets, and Kuiper belt objects.

Diameter(km) Earth Mars Jupiter Saturn Uranus Neptune Other objects
5000+

Ganymede Titan


4000-5000

Callisto


Mercury
3000-4000 The Moon
Io

Europa





2000-3000




Triton Pluto
1000-2000



Rhea

Iapetus
Dione
Tethys

Titania
Oberon
Umbriel
Ariel


90377 Sedna

(90482) 2004 DW
50000 Quaoar
20000 Varuna

28978 Ixion
100-1000

Himalia

Amalthea

Enceladus

Mimas
Hyperion
Phoebe
Janus
Epimetheus
Prometheus

Miranda

Sycorax
Puck
Portia

Proteus

Nereid
Larissa
Galatea
Despina

Ceres

Charon
2 Pallas
3 Juno
4 Vesta
(and many others)

50-100

Thebe

Elara
PasiphaŽ

Pandora Caliban

Juliet
Belinda
Cressida
Rosalind
Desdemona
Bianca

Thalassa

Naiad
S/2002 N 4

(Too many to list)
10-50
Phobos

Deimos

Carme

Metis
Sinope
Lysithea
Ananke
Leda
Adrastea

Siarnaq

Atlas
Helene
Albiorix
Telesto
Pan
Paaliaq
Calypso
Ymir
Kiviuq
Tarvos
Ijiraq

Ophelia

Cordelia
Setebos
Prospero
Stephano
S/1986 U 10
S/2001 U 2
S/2001 U 3
S/2003 U 3
Trinculo
S/2003 U 1
S/2003 U 2

S/2002 N1

S/2002 N 2
S/2002 N 3
S/2003 N 1

(Too many to list)
less than 10 Cruithne¹
Callirrhoe

Themisto
Praxidike
Megaclite
Kalyke
Iocaste
Taygete
Harpalyke
S/2000 J 11
Thyone
S/2003 J 6
Hermippe
Autonoe
S/2003 J 7
S/2003 J 5
S/2003 J 1
Chaldene
Isonoe
Erinome
S/2003 J 20
Euanthe
Eurydome
S/2002 J 1
Aitne
S/2003 J 8
S/2003 J 3
Euporie
S/2003 J 21
S/2003 J 18
S/2003 J 22
Orthosie
S/2003 J 16
S/2003 J 15
S/2003 J 17
S/2003 J 11
S/2003 J 19
Pasithee
Kale
S/2003 J 4
Sponde
S/2003 J 13
S/2003 J 23
S/2003 J 10
S/2003 J 14
S/2003 J 2
S/2003 J 12
S/2003 J 9

Erriapo

S/2003 S 1
Skathi
Mundilfari
Suttungr
Thrymr
S/2004 S2
S/2004 S1



(Too many to list)

¹ It is debatable whether Cruithne counts as a real moon; it is mainly placed here for comparison's sake.

See also

External links

Jupiter's moons

Saturn's moons

Neptune's moons

All moons



The Solar System
Sun | Mercury | Venus | Earth (Moon) | Mars | Asteroids
Jupiter | Saturn | Uranus | Neptune | Pluto | Kuiper belt | Oort cloud
See also astronomical objects and the solar system's list of objects, sorted by radius or mass


Last updated: 10-24-2004 05:10:45