Should we spend billions to monitor space and be able to destroy asteroids and other space junk?

Yes, though it should be a global effort. There are several spacefaring nations now, and many more with nice, dark skies that could host a telescope. The job of detecting and deflecting potentially damaging asteroids should not fall on one country's space program.

The search for potentially-hazardous asteroids already is a joint effort - NASA is partnering with observatories and universities in Spain, Australia, Chile, and a few other countries to survey the skies. This effort is now finding a few thousand asteroids per year and calculating their trajectories.

They can't capture everything with ground-based telescopes, however. The atmosphere distorts the sky too much. The meteor that fell over Russia was probably a meter or so in diameter - about the size of a desk. This would be virtually impossible to detect from the ground, so we'll need some space-based observatories if we want to really get serious about protecting ourselves from space rocks.

And then we've got to do something about the asteroid once we find it. This could be an opportunity for global cooperation, but maybe competition would be better. In fact, I'd like to see this become the new Space Race. Instead of competing to land on the Moon first, different nations should be racing to develop asteroid-deflection technology.

That way, we'll have some back-up plans in case one method fails.