The U.S. space agency is a decade behind in meeting a congressional mandate to detect meteors capable of destroying a city, and it needs a new telescope in space to improve tracking, the nation's top science officials said.

NASA's leaders said most asteroids large enough to trigger a global catastrophe have been found and tracked, and no impact within the next several centuries is likely. Smaller objects are harder to track and arrive more often.

"Unfortunately, the number of undetected potential 'city killers' is very large," John Holdren, assistant to President Barack Obama for science and technology, said yesterday at a hearing of the House Science, Space and Technology Committee. "It's in the range of 10,000 or more."

A meteor blast over Russia Feb. 15 that injured 1,200 people in Chelyabinsk put fresh focus on the concerns, and on exploring whether incoming space objects can be knocked off a collision course. The Air Force wasn't aware of the meteor until it streaked toward Earth, Gen. William Shelton said. He declined to elaborate.

Congress asked NASA to find and track 90 percent of the asteroids that are 140 meters or greater in size by 2020. Under current funding, the goal won't be met until 2030, Charles Bolden, the NASA administrator, said.

"Smaller objects, such as the recent impact in Russia will always be difficult to detect and provide adequate warning," Bolden said. But "if you really want to find and detect near-Earth objects early enough that we can do something, you need to have something in space," and that would cost billions of dollars, he said.

Scientists are powerless if a large asteroid big enough to threaten civilization was found to be on course to collide with Earth in a few weeks, Bolden said. "The answer to you, is, if it's coming in three weeks, pray," he said.

Latest Videos