With close encounters due in 2029 and 2032, space scientists are getting to grips with an existential threat

It is a scenario beloved of Hollywood: a huge asteroid, several miles wide, is on a collision course with Earth. Scientists check and recheck their calculations but there is no mistake – civilisation is facing a cataclysmic end unless the space rock can be deflected.

It may sound like science fiction, but it is a threat that is being taken seriously by scientists.