The big question from theoretical physicist and occasional blogger Dr. Michio Kaku isn’t “Can we terraform Mars for human habitation by bombarding it with comets and asteroids” but “Why haven’t we started yet?” After appearing on the Sci Fi channel to explain his idea, Kaku took to his blog to answer reader questions about what, exactly, he was talking about. He begins by dismissing the idea of terraforming Mars with nuclear power plants as the reckless insanity it obviously is, going on to explain his much more modest idea of shooting asteroids at the red planet’s surface. Kaku goes on to set up a timeline for terraforming Mars. He predicts the first astronauts will arrive “mid-century,” the first human colonies will be built “later in the 21st century,” and terraforming will happen in the “mid 22nd century.” Just to give a sense of scale, 2250 is 240 years from now; the date 240 years ago was 1770. So, according to Kaku, the distance between the American Revolution and today is roughly equivalent to the distance between today and the terraforming of Mars.