Such collisions have occurred throughout the history of the solar system, shaping and forming asteroids and planets. They realized their results might shed some insight on whether nuclear weapons could successfully deflect or destroy asteroids. In the case of solid rock, the smaller asteroid obliterates about 10 percent of Castalia and changes the speed of the rest of the asteroid by about 0.4 mph. That wouldn't be enough deflection to make the asteroid miss Earth unless the change in direction took place years before it was to hit. An object farther away needs to be knocked less, because the farther an object travels, the farther it veers from its original path.
Gravity pulls the fragments down onto the other, nearly unscathed rock.
The rubble pile structure dispersed the shock waves quickly. Although the crater blows half the rubble into space, the other half is nudged less than 1 mph. The other surprise was just how differently they responded to the impact. That, in turn, could help the Pentagon and the Energy Department design weapons to deflect or destroy threatening asteroids. The nuclear approach calls to mind two summer movies, Deep Impact and Armageddon .