Planet

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Image of the Solar System planets. Top image shows the Terrestrial planets and the bottom image shows the Gas giants.
Image of the Solar System planets. Top image shows the Terrestrial planets and the bottom image shows the Gas giants.

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.[1] All of these newly found planets are orbiting other stars: they are extrasolar planets. Sometimes people call them "exoplanets".

In the Solar System[change | change source]

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[change | change source]

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 Astronomical symbol for Mercury
Venus Astronomical symbol for Venus
Earth Astronomical symbol for Earth
Mars Astronomical symbol for Mars
Jupiter Astronomical symbol for Jupiter
Saturn Astronomical symbol for Saturn
Uranus Astronomical symbol for Uranus
Neptune Astronomical symbol for Neptune

Types of planets[change | change source]

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.

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

References[change | change source]

  1. Jean Schneider. "Interactive Extra-solar Planets Catalog". The Extrasolar Planets Encyclopedia. http://exoplanet.eu/catalog.php. Retrieved 2011-06-23.

Other pages[change | change source]