![Crescent view of Europa, one of Jupiter’s four large, Galilean moons, in a composite of images made …[Credits : NASA/JPL/University of Arizona]](http://media-2.web.britannica.com/eb-media/85/75385-003-EB1B47FD.gif)
any natural satellite orbiting another body. In the solar system there are 166 moons orbiting the planets. Earth, Mars, Jupiter, Saturn, Uranus, and Neptune have 1, 2, 63, 60, 27, and 13 moons, respectively. Other bodies in the solar system, such as dwarf planets and asteroids, also have moons. No moons have yet been discovered around extrasolar planets.
The solar system’s moons range in size from small bodies tens of metres across in orbit around asteroids to Saturn’s moon Titan, which has a diameter of 5,150 km (3,200 miles). Titan is so large that it is the only moon with an atmosphere.
Some moons are of interest because they have conditions that may be favourable for life. For example, Jupiter’s moon Europa has an ocean underneath its icy surface. Saturn’s moon Enceladus has geysers that spew out water and organic molecules.
The table lists some notable moons of the solar system.
| Notable moons of the solar system | ||||
| name | mean distance from centre of planet (orbital radius; km) | orbital period (sidereal period; Earth days) | radius or radial dimensions (km) | year of discovery |
| Earth | ||||
| Moon | 384,400 | 27.3217 | 1,738 | — |
| Mars | ||||
| Phobos | 9,378 | 0.31891 | 13.3 × 11.1 × 9.3 | 1877 |
| Deimos | 23,459 | 1.26244 | 7.5 × 6.1 × 5.2 | 1877 |
| Jupiter | ||||
| Amalthea | 181,400 | 0.498 | 83.5 | 1892 |
| Io | 421,800 | 1.769 | 1,821.6 | 1610 |
| Europa | 671,100 | 3.551 | 1,560.8 | 1610 |
| Ganymede | 1,070,400 | 7.155 | 2,631.2 | 1610 |
| Callisto | 1,882,700 | 16.69 | 2,410.3 | 1610 |
| Saturn | ||||
| Mimas | 185,520 | 0.942 | 199 | 1789 |
| Enceladus | 238,020 | 1.370 | 249 | 1789 |
| Tethys | 294,660 | 1.888 | 530 | 1684 |
| Dione | 377,400 | 2.737 | 560 | 1684 |
| Rhea | 527,040 | 4.518 | 764 | 1672 |
| Titan | 1,221,850 | 15.94 | 2,575 | 1655 |
| Hyperion | 1,481,100 | 21.28 | 185 × 140 × 113 | 1848 |
| Iapetus | 3,561,300 | 79.33 | 718 | 1671 |
| Phoebe | 12,952,000 | 550.4 | 110 | 1899 |
| Uranus | ||||
| Miranda | 129,800 | 1.413 | 235 | 1948 |
| Ariel | 191,240 | 2.520 | 580 | 1851 |
| Umbriel | 265,970 | 4.144 | 585 | 1851 |
| Titania | 435,840 | 8.706 | 789 | 1787 |
| Oberon | 582,600 | 13.463 | 761 | 1787 |
| Neptune | ||||
| Triton | 354,800 | 5.8768 | 1,353.40 | 1846 |
| Nereid | 5,513,400 | 360.1468 | 170 | 1949 |
| Pluto | ||||
| Charon | 19,640 | 6.3873 | 625 | 1978 |
Crescent-view-of-Europa-one-of-Jupiters-four-large-GalileanCrescent view of Europa, one of Jupiter’s four large, Galilean moons, in a composite of images made …[Credits : NASA/JPL/University of Arizona]
False-colour-images-of-the-ring-and-satellites-of-SaturnFalse-colour images of the ring and satellites of Saturn, taken by the Hubble Space Telescope, Nov. …[Credits : Photo AURA/STScI/NASA/JPL/Caltech (NASA photo # PIA01271, STScI-PRC96-18b)]
Jupiters-moon-Io-with-Jupiter-in-the-background-photographed-byJupiter’s moon Io with Jupiter in the background, photographed by the Voyager 1 spacecraft on March …[Credits : Photo NASA/JPL/Caltech (NASA photo # PIA00378)]
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