Dr. Michio Kaku is on a mission to save planet Earth. Nearly 90 percent of the rocks in space are big enough to destroy our civilization. And it's not a question of if they'll hit our planet, but when. He shows what would happen if we really did use nuclear weapons to blow up an incoming asteroid and comes up with a safer, rocket-powered solution. Kaku meets up with Harvard's Professor Brian Marsden, who explains how a massive comet could smash into Earth without warning. To deal with the multiple threats, Kaku takes a lead from Star Wars and designs a system of laser-equipped Death Stars to zap the space rocks before they hit us.