Asteroid deflection methods, illustration. Large asteroids can cause global devastation and mass extinctions if they impact the Earth. Across top, a missile with a nuclear warhead is being exploded on or near to an asteroid that is threatening the Earth. Rather then destroy the asteroid (upper left), the explosion is designed to deflect the asteroid's orbit (upper right). The same effect is achieved by landing a thruster on the surface of the asteroid (centre left). At centre right, a spacecraft drops 'soot' on the asteroid. The effect of this (lower left) is to increase radiation (yellow arrows) from the warmer 'sooty' surface, leading to a small but sufficient deflection of the orbit (red arrows). Finally, at lower right, simply flying a sufficiently massive 'tractor' spacecraft alongside the asteroid will slightly alter the asteroid's orbit due to gravitational attraction (yellow arrow).