What are the chances of the Earth being hit by an asteroid - another and much smaller world orbiting the Sun? Just over 40 years ago the Earth was nearly in collision with an asteroid called Hermes. Statistically the danger of a collision is slight, but by no means nil. In America the NASA authorities have announced plans for destroying any approaching asteroid with a nuclear missile. Can we predict the possibility of a collision? In this programme Patrick Moore discusses the whole question of asteroid collisions with Dr David Hughes of Sheffield University.