Faulkes Telescope Educational Guide

Planets

There are nine planets in our Solar System. In order, from the Sun outwards, they are:

Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto

The first four are called the "terrestrial" planets. They are made of rock, like the Earth, with iron in their centres. The next four are called jovian planets, meaning ‘Jupiter-like’ and they are made mainly of gas. Pluto is rocky like the terrestrial planets, but it is so small that many astronomers think that it is not a planet at all, but is part of a group of rocky objects called the Kuiper Belt. In between Mars and Jupiter, there is an asteroid belt containing thousands of rocky asteroids, ranging in size from a few centimetres to a few kilometres.

How the Solar System was Formed

The Solar System was made from a giant spinning cloud of gas and dust. This cloud collapsed under its own weight to form the Sun, surrounded by the left-over dust and gas. Because the cloud was spinning, this left over stuff was flattened into a disc around the young star. The planets formed from this disc. Scientists are unsure exactly how this happened but somehow the tiny dust grains clumped together to make planets thousands of kilometres across.

There are many clues that the Solar System formed from a giant disc: all of the planets move around the Sun in the same direction and as if they were all on one flat surface – called the “ecliptic plane”. Almost all of the planets spin in the same direction, and the Sun also spins in this direction.

We can see other solar systems being formed in a huge cloud of dust and gas called the Orion Nebula.

Click on the links below to find out more about our Solar System:

		Mercury
		Venus
		Earth
		The Moon
		Mars
		Jupiter
		Saturn
		Uranus
		Neptune
		Pluto
		Asteroids
		Comets
		Meteorites
		Extra-Solar Planets

Authors: Carolyn Brinkworth and Claire Thomas

Last updated: July 2001