Asteroids are ancient space rocks left over from the formation of the Solar System, thought to have brought complex molecules and possibly early life to Earth, billions of years ago. The Chicxulub asteroid is probably the most famous space rock in the world. Although you may not know its name, its impact 66 million years ago is legendary – causing a mass extinction event that saw most non-flying dinosaurs and many other species wiped out. Impacts from such large asteroids are immensely rare, but small- and medium-sized rocks are far more common in the Solar System and can still do serious damage.