Threats from space
Earth is the largest of the four rocky planets in our Solar System. It is very heavy for its size. At its centre is a large, iron-rich core, where the temperature reaches 6000 degrees Celsius – as hot as the surface of the Sun.
The liquid outer core churns around as the planet spins, acting like a dynamo on a bicycle. This dynamo causes the Earth to behave like a strong magnet.
Forming an invisible bubble around the planet, Earth's magnetic field acts like a shield. This protects the planet from most of the high speed particles blasted into space by solar storms. Sometimes particles break through the barrier near the magnetic poles. This results in Earth's auroras – commonly known as the Northern and Southern Lights.
Earth's surface is also protected by the thick atmosphere. This blocks out most of the harmful radiation from space. It also causes small incoming objects to burn up as shooting stars. Only the larger meteorites and comets reach the surface and explode, leaving large craters.
Unlike the Moon and other rocky planets, there are few impact craters on Earth today. Most of them have been worn away or filled in by the action of flowing water, wind and ice.
Last modified 06 December 2004