to miss us by a cosmic inch, just 17,000 miles. That's closer than some of our weather satellites. In fact, it's so close scientists are springing into action and here's abc's nearly neal karlinsky.... See More
to miss us by a cosmic inch, just 17,000 miles. That's closer than some of our weather satellites. In fact, it's so close scientists are springing into action and here's abc's nearly neal karlinsky. Reporter: Right now, you're watching this -- a chunk of space rock big enough to level a city is heading toward our speeding bullet. The good news -- scientists say it will miss. The scary news -- the 130,000 met rein ton asteroid called da- 14 -- is the size of half a football field and it will be much closer than the moon. It will thread the needle between earth and the roughly 600 satellites around us, the ones that your cellphone relies on, possibly smashing one on its way by. But that's while you're thinking all of that is still a long, long way from all of us way down here, walking the streets -- you want to think again. The last close call turned out to be a direct hit. It was 1908 and the only thing -- luckily, it hit the middle of nowhere, siberia. Decimating a thousand miles of trees, but no people. If a very large asteroid hit, I am talking about something that is miles across, it would probably create the same kind of disaster that wiped out the dinosaurs. Reporter: Amazingly, no one knew d4-14 was headed our way until a spanish dentist and amateur astronomer randomly discovered it a year ago. Nasa doesn't have the resources to look for asteroids. Which is why a trio of american astronauts and rocket scientists are raising money to launch their own asteroid warning system called sentinel -- a dedicated telescope scanning the stars for threats. This asteroid is a wake-up call. We should be looking out there. Things do hit the earth. But scientists say we can keep the planet safe if we just know what's out there, headed our way. Neal karlinsky, abc news, seattle.
This transcript has been automatically generated and may not be 100% accurate.