* Director, Spaceguard Centre
* Knighton, Wales
* Professor of Earth Sciences
* University of California, Santa Cruz
Santa Cruz, California
*Manager, Near Earth Object Program
*Jet Propulsion Laboratory
Sixty five million years ago, scientists say, an asteroid the size of a small city obliterated the dinosaurs. Are more killer asteroids on their way? Scientists around the world are scanning the heavens for dangerous Earth-bound objects, but the question remains — if they find them, can they be stopped? On this hour of Science Friday we'll talk about close encounters with asteroids, and plans for an asteroid defense system.