Deflecting an asteroid, with paintballs

In the event that a giant asteroid is headed toward Earth, you'd better hope that it's blindingly white. A brightly colored asteroid would reflect sunlight — and over time, this bouncing of photons off its surface could create enough of a force to push the asteroid off its course.

How might one encourage such a deflection? The answer, according to an MIT graduate student: with a volley or two of space-launched paintballs.