Eyeing the sky for danger

There are a million asteroids in space big enough to destroy a city, and scientists only know where one percent of them are

Though scientists are keeping an eye on most of the large asteroids and comets capable of causing global destruction by colliding with Earth, they have been able to track only one percent of the smaller ones that are capable of destroying an entire city, Anderson Cooper reports this Sunday on 60 Minutes.

Cooper's story also reveals that NASA scientists first learned about the asteroid that exploded in Russia in February from Twitter and YouTube. There was no advance warning. "We didn't see it coming," say Paul Chodas, a scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "It was coming from the general direction of the sun, so it was in the daytime sky as it approached."

Cooper's report will be broadcast on 60 Minutes Sunday, Oct. 6 at 7:30 p.m. ET/PT. The segment explores the scientific importance of near-Earth objects -- comets and asteroids whose orbits bring them close to the Earth -- as well as the difficulty scientists have detecting many of them.

Scientists estimate there are over a million objects that come near Earth and are large enough to destroy an entire city. Ed Lu, a former astronaut, uses a computer representation of our solar system to show Cooper the 10,000 asteroids astronomers have found so far. It's just the tip of the iceberg, Lu says. "We've only been able to observe a small fraction of the sky and we know that there are about 100 times more asteroids than we've found...about a million asteroids big enough to destroy a city out there," Lu tells Cooper.

Paul Chodas and his boss Don Yeomans, manager of NASA's Near Earth Object Program Office, tell Cooper that asteroids capable of destroying a city are relatively small (over 40 yards wide) and are likely to land in uninhabited areas or in the ocean if they were to collide with Earth. That's why NASA has focused on finding the larger objects that could do much greater damage first and will then work its way down to the smaller ones, Chodas says.

If astronomers find an object that is on a collision course with Earth many years in advance, then it would be possible to ram an unmanned spacecraft into the object and deflect it away from Earth, Yeomans and Chodas say. But it's impossible to deflect what you have yet to detect, which is why new tools may be needed.

Former astronaut Ed Lu, who is now chairman and CEO of the B612 Foundation, is trying to raise private funds to build a space-based telescope that would use infrared sensors to detect near-Earth objects. Asteroids are often dark and difficult to detect in the inkiness of space, but an infrared telescope would notice the heat they emit, making them much easier to spot.

"I don't think there's any other... global-scale catastrophe that we can prevent...for the cost of building a freeway overpass," says Lu.

Over long periods of time, Lu argues, the odds are high that there will be more impacts. He says it's like a game of "cosmic roulette," but one that mankind cannot afford to lose.

"The phrase that they have in Vegas is that the house always wins, right?" Lu tells Cooper. "The sort of secret to all this is we're not the house. At some point...the solar system's going to get you."