"Nemesis is the name given by scientists to a (theoretical) small companion star to our sun. Every 26 million years, the theory postulates, Nemesis's orbit brings it close enough to the sun to bombard our solar system with billions of comets. While most of the comets will float harmlessly away, some will be thrown toward Earth. Such a "large-body impact," the Nemesis theory holds, was responsible for the mass extinction that led to the demise of the dinosaurs. David M. Raup draws on wide research to set forth the evidence - or lack of it - for this revolutionary theory, along the way opening a revealing window on how science works, belief systems in science, and the influence of the press and popular culture on the circulation of scientific ideas."--BOOK JACKET.