>> reporter: they know because of that boom. a 4 kiloton explosion. >> it shook a lot of houses and buildings on the ground. >> reporter: nasa is already working on the armageddon scenario. developing a small probe to ram asteroids and knock them off course. they've even tested it successfully. all that's left of this one are tiny rocks no bigger than a baseball. >> but the men in black are on it? >> they'll be on it. >> reporter: david wright, abc news, pasadena. >> pretty amazing stuff. >> every year at this time the earth passes through the orbit of an old comet and the result is a meteor shower. >> whoa, man. >> check out our cracked meteor. >> it's rough out here, man. what's up, man? it's brutal out here on overnights. what is this? i'm throwing this back out. get out of here. >> two points. swish with the meteor. >> those aren't the kind of rocks they are used to in vegas. i'll tell you that. this is a very serious network news. welcome back to the overnight.