An asteroid half the size of a football field passed dangerously close to the Earth today, coming inside the orbital distance of some of our own satellites, in fact. And following news this morning that a meteor struck near an industrial city in Russia and injured more than 500 people, the question remains: what if a big rock his someplace dense, like Moscow? Or Shanghai? Or New York? It would explode in the atmosphere about at the cruising altitude of most passenger jets, with the force of an atomic bomb 138 times more powerful than the one that the U.S. dropped on Hiroshima. At that power, it wouldn’t have to hit a city to create the worst day in life insurance history. It would just have to land in the same county.