Planets

Planets are lumps of gas and rock held close to a star by the force of gravity. We live on planet Earth going round star Sun, along with severn other planets and thousands of smaller objects. Together these are called the Solar System.

Because stars form in dark clouds of dust and molecules in open star clusters, it is difficult to watch them form. So the story of how planets formed which we have just given has not been confirmed by observation.

Although they are all difficult to see, hundreds of planets have been discovered near Sun-like stars. Looking for planets near a star is a bit like trying to watch a moth flying around a spotlight which is pointing at you -- you get dazzled by the light.

Since discs of gas and dust have been detected around some young stars, we guess that planets might be common. But none of the planets so far discovered are like our Solar System. Indeed these discoveries are challenging current theories of the origin of planets.

If planets like ours are common, then life too could be common in the Galaxy.

Artist's impression of star birth copyright Joe Tucciarone

Here we give a brief overview of planets orbiting the Sun. In the Reference Section we describe them in a little more detail.

Recent discoveries of planetary systems outside our own are challenging current ideas on how the Sun and its eight planets, the solar system, originally formed. The story which follows, therefore, may soon be changed in the light of new discoveries.

First we describe current ideas of how they formed.