Mercury  Venus   Earth    Mars     Jupiter      Saturn        Uranus      Neptune     Pluto
(Planets are not to scale.)
Classification of the Solar System
The planets of the solar system can be classified in different ways
  1. by size
  2. by composition (or what they are made of)
  3. by distance from the Sun
  4. by history (when they were discovered)

 

Classification by Size
  1. There are the small planets: Mercury, Venus, Earth, Mars and Pluto. These planets have diameters less than 13000 kilometres. Mercury and Pluto are sometimes referred to as lesser planets (not to be confused with minor planets which is the official term for asteroids).

  2. There are also the giant planets: Jupiter, Saturn, Uranus and Neptune. The giant planets have diameters greater than 48000 kilometres. These planets are sometimes also called the gas giants.

Classification by composition
  1. There are terrestrial, or rocky planets, the ones made up mostly of rock and metal. These planets are Mercury, Venus, Earth and Mars. The terrestrial planets are have relatively high densities, slow rotation, solid surfaces, no rings and few satellites.
  2. Then there are the jovian or gas planets. These planets are Jupiter, Saturn, Uranus and Neptune. The gas planets are made up mostly of hydrogen and helium. They and usually have low densities, rapid rotation, deep atmospheres, rings and lots of satellites.
  3. Pluto is an exception as it thought to be made up of a mixture of rocks and several kinds of "ices". Scientists believe that most of these ices are that frozen gases and liquids such as methane and ammonia.
    4.

Distance from the Sun
  1. There are the inner planets: Mercury, Venus, Earth and Mars.
  2. Then there are the outer planets: Jupiter, Saturn, Uranus and Neptune and Pluto
  3. The asteroid belt between Mars and Jupiter forms the boundary between the inner solar system and the outer solar system.
    4.

Historical Classification
  1. There are the classical planets: Mercury, Venus, Mars, Jupiter, and Saturn. These planets have been known since prehistorical times. They can all been seen from Earth without the use of binoculars or telescopes.
  2. There are also the modern planets: Uranus, Neptune, Pluto. These have been discovered since the invention of telescopes since they are only visible with telescopes.
  3. There is also Earth.
    4.

Resources Used
Astronomy for Kids www.dustbunny.com/afk/
Small Worlds David Drew: Nelson, 1989
The Gas Giants David Drew: Nelson, 1989
Solar System Unit Glossary
Images from: Astronomical Pictures & Animations Astronomy Picture of the Day Welcome to the Planets
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