Asteroid deflection. Artwork of a near-Earth asteroid being pulled by a solar sail. Light photons from the Sun exert tiny amounts of pressure on the sail which enables it to accelerate and pull the asteroid 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).