AP Photo

Lurking in space are asteroids even bigger than the city busters—to wit, “nation busters” big enough to destroy Germany or England. The most dangerous one is called Apophis, which is 1,000 feet across and will come dangerously close to Earth in 2029 and again in 2036. The most recent calculations show that Apophis will barely miss Earth in 2029, but will actually graze our atmosphere. But because of the uncertainty of its path as it whizzes past, there is a small possibility that its orbit may be perturbed so it might actually hit Earth in 2036. NASA scientists are reasonably confident it will still miss Earth in 2036, but the head of the Russian space agency takes the threat of a collision seriously, stating that we have to prepare for the worst. If Apophis hits...