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The Solar System


The big hot ball at or near the centre of the Solar System. More information is on the Sun page.


The definition of a planet (as of September 2006) states that, in the Solar System, a planet is a celestial body which:

  1. Is in orbit around the Sun,
  2. Has sufficient mass to assume a nearly round shape, and
  3. Has "cleared the neighbourhood" around its orbit.

The Solar System has 8 planets. In order from the Sun they are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. More information is on the Planets page.

Natural satellites (moons)

Moons are objects that orbit planets or minor planets. In other words, natural satellites. There are 173 known natural satellites in the Solar System.

Around planets, they come in all sizes, from Ganymede (5,268 km across, orbiting Jupiter) down to Deimos (7km across, orbiting Mars). Our Moon is one of the larger ones (3,474 km across), and is the largest moon in the Solar System relative to the size of the planet it's orbiting.

Around minor planets, even smaller natural satellites are known. The asteroid 243 Ida has a moon named Dactyl which is just 1.4 km across.

Minor planets

A minor planet is not a planet, but may be a number of things, which are dealt with on the Minor Planets page.

  • Dwarf planets.
  • Asteroids.
  • Trojans.
  • Centaurs.
  • Kuiper belt object, or other trans-Neptunian object.


A comet is an icy body orbiting the Sun that slowly boils off, producing a long tail. More information is on the Comets page.

Meteors and Meteorites

Small rocky bodies that enter Earth's atmosphere. More information is on the Meteors and Meteorites page.