(CBS News) "One of these days, an object with our name on it is going to hit the Earth," according to Michio Kaku, "CBS This Morning" contributor and physics professor at City College of New York, about the threat of an undetected asteroid or comet colliding with Earth.
It's happened before -- most recently in Russia, when a meteorite struck the city of Chelyabinsk, damaging buildings and injuring hundreds.
But before you go out and buy a helmet to protect yourself from falling space rocks, Kaku put the risk in perspective on "CTM," noting that the frequency with which "city-busting" sized meteorites strike the planet is about once every 100 to 200 years.
But there is still a real danger of smaller asteroids -- those about the size of a football field -- slipping by undetected because there is no formal program designed to search for them. Kaku suggests building an early-warning telescope dedicated to this purpose.
"It would cost chump change - a few hundred million," he said. "But we have the giggle factor. Every time you talk to a politician about asteroids they start to giggle."
He calls the meteorite that struck Russia in 2013 a "wake-up call" because if that hit the Earth, instead of exploding in outer space, it would've hit with the force of 20 Hiroshima bombs.
"The dinosaurs did not have a space program," Kaku said, "and that's why they're not here today. But we do have a space program but even then, we are sitting ducks."
For more with Kaku, watch his full interview above.
Editor's note: An asteroid is a rocky body in space. It's called a meteor once it enters the atmosphere, and a meteorite once it hits the ground.