Asteroid deflection. Artwork of astronauts travelling over the surface of an asteroid. They will install nuclear bombs which, upon detonation, will vaporise a small portion of the asteroid which should deflect it's path away from an Earth- bound trajectory. 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).