Out of this World

Otherwise known as the Sun, it is the centre of our Solar System and was formed from the collapse of a giant molecular cloud about 4.6 billion years ago. Eight main planets revolve around the Sun and are kept in their roughly circular orbits by gravity. Between the four small inner planets and the four large outer planets lies the asteroid belt, a ring of hundreds of thousands of small, odd-shaped bodies made of rock and metal. Beyond Neptune there are five small, icy dwarf planets. One of them is Pluto.

The four closest planets to the sun are categorised as the terrestrial planets, which are primarily composed of rock and metal. They are Mercury, Venus, Earth and Mars. The four outer planets are much bigger than the terrestrials. The gas giants, Jupiter and Saturn, are mainly composed of helium and hydrogen. The ice giants, Uranus and Neptune, contain ices of water, ammonia and methane.

There are billions of solar systems in the known Universe. Our Solar System is like a tiny island within a constantly expanding cosmic ocean. Unfortunately mankind has not yet travelled to other solar systems, but we have managed to explore and document the beauty of ours for many years from unmanned robotic spacecraft. Here’s some of what we’ve learnt about the planets in our Solar System, which were all named after Roman gods.

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