As the universe evolved, vast clouds of gaseous material called nebulae formed and about 4.6 billion years ago, just such a nebula formed in the neighbourhood where our solar system is now situated. It also covered a much larger area than our present system.
Very slowly particles within the nebula began to come together to form larger and larger clumps of matter. As these pieces grew in size, the force of gravity associated with their mass grew a little stronger and gradually attracted more and more particles and matter to them. The first and largest sphere to be formed was our Sun. In a future article about our Sun we shall discuss how it came to produce the light and energy we need to survive upon the Earth.
Other smaller spheres formed and these became the inner rocky-metallic planets of Mercury, Venus, the Earth and Mars. Then the outer planets were formed. They are the gas giants of Jupiter, Saturn, Uranus and Neptune. These planets first formed a rocky core and then drew in gas from the surrounding nebula to form their thick gaseous atmospheres.
Between the outer of the rocky planets, Mars and the inner of the gaseous giants, Jupiter, we find the Asteroid Belt. This consists of billions of rocks of various sizes. They orbit the Sun between these two planets.
In addition there are a number of minor or dwarf planets. The most famous of these is Pluto. Until 2006 it was considered as the ninth and outermost planet in our solar system. But a committee decided that it did not merit full planet status and consigned it to a minor role.
At the outermost reaches of the solar system we find the Kuiper Belt and Oort Cloud. These are areas which contain thousands of comet-like objects, the minor planet Pluto and other dwarf planets.
So starting at the centre of our solar system and moving out we have the Sun, Mercury, Venus, Earth, Mars, the Asteroid Belt, Jupiter, Saturn, Uranus, Neptune, the Kuiper Belt and the Oort Cloud.
There are also “solo travellers” within the solar system. These are single comets and asteroids that have “broken loose” and follow their own particular orbits around the Sun.
But we have left another set of objects to the last. These are the various moons which orbit many of the planets in the solar system. The most well-known and visible one is our own Moon. However, at the present time, we have discovered over 140 moons in orbit around the various planets and in future articles, we will discuss all of these objects in more detail.
John Pullen 