Earth is constantly bombarded by objects from outer space - about 500,000 meteoroids enter the planet''s atmosphere every day, though only a small fraction reach the surface. Most of these space-rocks pose no danger to the inhabitants of Earth, however according to scientists, every ten million years or so, a truly massive asteroid hits our planet causing global devastation ? the last such event took place 65 million years and resulted in the extinction of dinosaurs. There are currently 1203 known hazardous near earth objects identified by NASA''s Near Earth Object Project. Learn more about them in this book.