The researchers constructed a mathematical representation of the irregularly spaced near Earth asteroid Castalia for their calculations. They assumed it would be made of solid rock, a pair of solid rocks separated by rubble, or a 50% porous agglomeration of large boulders. To simulate a collision they imagined a 8m diameter basalt sphere travelling at 5 kms-1 hitting the asteroid. This would impart a explosive force equivalent to a 17 kiloton nuclear device. They found that in most cases only 10 percent of the asteroid's mass reached escape velocity, the rest of the material stayed loosely bound in the area. A hard rock object on the otherhand was more likely to simply split into two. As well as suggesting that deflecting or destroying asteroids may not be as easy as first thought, it also suggests that most binary asteroids were formed in collisions this way.