S1, E4: In this second hour of Doomsday Tech, we look at more of the threats-both natural and manmade-that may endanger civilization. From the reaches of space to tiny viruses inside our bodies, the sources of doomsday are many. But so are the technologies used to keep doomsday at bay. We begin with killers from space. Not little green men, but mile-wide chunks of rock traveling at 36,000 miles per hour: asteroids. Asteroids of significant size have hit the Earth before, and they will hit it again with planet devastating intensity. In fact, a series of close calls in the past several years have prompted an acceleration of the world's asteroid hunting programs. We'll meet some of the world's foremost asteroid hunters, from NASA and JPL, who will show us the Near Earth Asteroid Tracking (NEAT) program. We'll not only check out the telescopes and enormous digital cameras used to track the asteroids; we'll examine the methods being developed to nudge or destroy an asteroid that sets its sights on Earth.