As end-of-the-world scenarios go, an apocalyptic collision with an
asteroid or comet is the new kid on the block, gaining respectability only in
the last decade of the 20th century with the realisation that the dinosaurs had
been wiped out by just such an impact.

Now the science community is making up for lost time, with
worldwide efforts to track the thousands of potentially hazardous near-Earth
objects, and plans for high-tech hardware that could deflect an incoming object
from a collision course - a procedure depicted, with little regard for
scientific accuracy, in several Hollywood movies.

Astrophysicist and science writer Andrew May disentangles
fact from fiction in this fast-moving and entertaining account, covering the
nature and history of comets and asteroids, the reason why some orbits are more
hazardous than others, the devastating local and global effects that an impact
event would produce, and - more optimistically - the way future space missions
could avert a catastrophe.