Asteroids are rocky and metallic objects too small to be considered planets. They are sometimes called minor planets. The name asteroids means "star-like". In the night sky asteroids look like stars since they do not emit gases and dust like comets.
Asteroids on a collision course with Earth are called meteoroids. When a meteoroid burns up as it falls through our atmosphere, it is called a meteor, or "shooting star". If a meteoroid crashes into the Earth it is called a meteorite.
The main asteroid belt orbits between Mars and Jupiter. It is thought that asteroids are remnants of the rotating disk of dense gas surrounding our Sun when it was a young newly formed star. The material was unable to fuse together into a planet because of the powerful gravity of Jupiter.
Some asteroids have moons or are found in pairs known as binary systems. The total mass of all the asteroids is less than that of the Moon.
Image : Tobias Mixer