The drawback to Lu’s plan is that it would work only for asteroids up to a few hundred meters across that could be engaged far from Earth. If the rock is small, we could try hitting it with a spacecraft. When all else fails, and for large asteroids and comets, only one strategy has a chance of working: nuclear bombs. Russian scientist Vadim Simonenko and his colleagues concluded that the best way to deflect an asteroid up to 1.5 kilometers (one mile) or so wide would be to explode a nuclear bomb nearby. The explosion would destroy smaller rocks. For larger ones, the explosion would burn a layer of rock off the asteroid’s surface. The expanding gas would act as a rocket motor, pushing the asteroid onto a new course.