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A planet is a large object such as Jupiter or Earth that orbits a star. It is smaller than a star, and it does not make light. Planets are ball-shaped (spheres). Objects that orbit planets are called moons. There are eight planets in the Solar System. Pluto used to be known as a planet, but in August 2006, the International Astronomical Union decided it was a dwarf planet instead. There are four more known dwarf planets in the Solar System, Ceres, Makemake, Eris and Haumea.
The name "planet" is from the Greek word πλανήτης (planetes), meaning "wanderers", or "things that move". Until the 1990s, people only knew of those in the Solar System. As of June 2011, we know of 563 other planets. All of these newly found planets are orbiting other stars: they are extrasolar planets. Sometimes people call them "exoplanets".
In the Solar System
The planets in the Solar System have names of Greek or Roman gods, apart from Earth, because people did not think Earth was a planet in old times. However, Earth is occasionally referred by the name of a Roman god: Terra. Other languages, for example Chinese, use different names. Moons also have names of gods and people from classical mythology, or from the plays written by Shakespeare.
Here is a list of planets in the Solar System. They are ordered by how close they are to the Sun, nearest first.
Types of planets
Astronomers speak about major (or true) planets, and minor planets, which are smaller objects that go around the Sun. Some examples of "minor planets" are asteroids, comets, and trans-Neptunian objects.
Planets in the Solar System are of three sorts:
- Terrestrial or rocky: Planets that are similar to Earth — in them is mostly rock: Mercury, Venus, Earth, Mars
- Jovian or gas giant: These planets are mostly made of gas: Jupiter, Saturn, Uranus, Neptune. Uranian planets are a special sort of gas giants, they have more hydrogen and helium.
- Icy: Sometimes people also have a third sort, for bodies such as Pluto (though Pluto is no longer called a planet by everyone). These planets are mostly made of ice.
- Jean Schneider. "Interactive Extra-solar Planets Catalog". The Extrasolar Planets Encyclopedia. http://exoplanet.eu/catalog.php. Retrieved 2011-06-23.
The Solar System
☾ = moon(s) ∅ = rings
|Mercury||Venus||Earth ☾||Mars ☾|
|Jupiter ☾ ∅||Saturn ☾ ∅||Uranus ☾ ∅||Neptune ☾ ∅|
|Dwarf planets||Ceres||Pluto ☾||Haumea ☾||Makemake|
| Groups and families: Vulcanoids · Near-Earth asteroids · Asteroid belt |
Jupiter Trojans · Centaurs · Neptune Trojans · Asteroid moons · Meteoroids · Pallas · Juno · Vesta · Hygiea · Interamnia · Europa
|See also the list of asteroids.|
|Kuiper belt – Plutinos: Orcus · Ixion – Cubewanos: Varuna · |
Quaoar · Huya
|Scattered disc: Sedna|
|Comets|| Periodic comets and non-periodic comets |
Damocloids · Oort cloud
|See also the list of solar system objects|