[SunkenCiv]

Would the last person to leave the Earth turn off the, oh, never mind. That last flash of light shouldn't last that long...

Asteroid-impact Study Finds Effects Of Collisions Or Explosions On Small Asteroids May Be Hard To Predict
by Tim Stephens
June 8, 1998

Astronomer Erik Asphaug, a UCSC research associate, used computer simulations to study the effects of powerful impacts on asteroids with different internal structures. He and his colleagues found that the outcome of such impacts depends on the degree to which the asteroid has been fractured and made porous by earlier collisions. "It's a lot more difficult to nudge these asteroids around than we had thought."

Deflecting Asteroids Harder Than Once Thought
June 4, 1998

The fractured, porous nature of many asteroids may make it difficult to use nuclear weapons or other explosions to nudge them off collision courses with the Earth. The effects of a collision or explosion on an asteroid depend strongly on the interior structure of the asteroid. A solid asteroid, they found, might easily shatter when hit by another asteroid. However, a more porous asteroid, one fractured by previous collisions, would tend to damp out the effects of the collision.

[SunkenCiv]

Wanted: small asteroid for use as slingshot to slay a Goliath
by Ian Sample
The Guardian
Saturday July 15, 2006

Scientists at the French space agency, CNES, have calculated how to capture an asteroid and manoeuvre it into a near-Earth orbit, from where it can be flung into the path of a larger asteroid that threatens to collide with Earth... Writing in the journal Acta Astronautica, the scientists show how the asteroid... could be kept in a holding position until it needed to be redirected to intercept a much larger "Goliath". Even if the incoming asteroid was 1,000 times heavier than the orbiting asteroid, the two would still collide at a speed of 23km a second, generating 4 million billion Joules of energy, the equivalent of 40 Hiroshima bombs.