So when Clarke published his novel The Hammer of God, about just such an effort, in 1993, he did not consider it merely science fiction. "It was my duty to show what could be done about the asteroid menace," he wrote. "By creating a self-fulfilling prophecy, I might even save the world – though I"d never know." The following year, 21 fragments of the comet Shoemaker-Levy 9 collided with Jupiter, giving NEO-watchers a preview of what one might do to us. One of the impacts was equivalent to six million megatons of TNT, creating a cloud of debris as wide as Earth.