Planet

Terrestrial planets.

Gas giants planets and the Sun.

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

Main page: History of astronomy

Planets from 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.

Planets

Here is a list of planets in the Solar System. They are ordered by how close they are to the Sun, nearest first.

Planet	Symbol
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune

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.
• Gas giant or Jovian: 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.
• Ice dwarf or 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.

Many objects in the Solar System that are not planets are also "icy". Examples are the icy Satellite (moons) of the outer planets of the Solar System (like Triton).

See also

• List of planets

Mercury •

Venus •

Earth •

Mars •

Jupiter •

Saturn •

Uranus •

Neptune

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