Asteroid deflection. Artwork of an impact flash caused by the collision between an unmanned spacecraft and an asteroid. The collision is an attempt to create momentum and deflect the asteroid from hitting the Earth. This method is known as kinetic impactor deflection. Asteroids are minor planets with diameters of less than 100 kilometres. A collision with Earth would cause massive tsunamis if it hit the oceans and block sunlight due to the huge quantities of dust thrown in to the stratosphere. It is thought that the extinction of the dinosaurs around 65 million years ago was caused by an asteroid impact. An asteroid, comet or other large body posing a danger to Earth is known as a Near-Earth Object (NEO).