Paintballs to Stop Asteroid Impacts
I cannot guess how many movies, books, and games have suggested the end of humanity coming about due to an asteroid impact, which has been known to cause mass extinctions before. Though much of the literature on the subject is fictitious, this is a real danger and researchers are looking for ways to prevent it from happening. One new idea from a researcher MIT is somewhat intriguing though, as it combines two approaches.
An obvious way to stop an asteroid would be to hit it with something hard enough, that it is deflected and does not impact the Earth. What the MIT researcher has added is a change to what you hit the asteroid with. Instead of a simple projectile, paintballs could be used, or some other fragile object containing paint. While the impact with the paintballs itself can deflect an asteroid, the change in reflectivity can also cause the asteroid to change course. Photons, despite being massless, have momentum, so when they hit something, they exert a force on it. Covering an asteroid in white paint will increase this force enough to move the asteroid more than the initial impact did.
It is worth noting that this affect could require years to deflect an asteroid enough to preserve humanity, but for those asteroids that threaten Earth, that is plenty of time. Well, at least the ones we know about.