Fifteen years ago, in the movie "Armageddon," Bruce Willis led a team of roughneck astronauts who tried to blow up a threatening asteroid with a nuclear weapon. Lu and other scientists -- even those who spend their careers watching for threats -- say the reality would be much less dramatic. If you spot an incoming asteroid well in advance -- and that's the idea behind Sentinel -- you just have to nudge it ever so slightly.
Lu and astronaut Stan Love have proposed a space tug, a rocket that would launch to the same orbit as an asteroid threatening to hit the Earth, and push it just enough to make it harmless.
"You don't have to change much. One hundred thousandth of a mile an hour is enough, 10 years ahead of time, to cause an asteroid to miss the rendezvous with Earth," Lu said.
With this month's visitor, 2012 DA14, no action will be necessary. Some scientists will use the opportunity to take a relatively close-up look at a passerby; others say to think of it as a sort of shot across our bow.
"We have been given a gift, the ability to protect our planet," Lu said. "We shouldn't squander it."