Maybe we won't all die soon, after all

NASA has found more than 90 percent of the biggest asteroids that come close enough to Earth to be a worry, the space agency said Thursday. It's also cut by more than a third the number of mid-sized asteroids that could be a threat.

Astronomers using the Wide-field Infrared Survey Explorer, or WISE, said they now estimate there are 19,500 mid-size near-Earth asteroids, a big decrease from the previous estimate of 35,000. That means it's possible, but not certain, that the threat to Earth is not as bad as feared.

"The risk of a really large asteroid impacting the Earth before we could find and warn of it has been substantially reduced," Tim Spahr, director of the Minor Planet Center at the Harvard Smithsonian Center for Astrophysics, said in a statement.

The results come from what NASA calls the most accurate census to date of near-Earth asteroids, those that orbit within 120 million miles of the sun and also near Earth's orbit. The researchers didn't count every single asteroid but took a representative slice, they write in the Astrophysical Journal.

"It's like a population census, where you poll a small group of people to draw conclusions about the entire country," said Amy Mainzer of NASA's Jet Propulsion Laboratory, who led the study.

They found 93 percent of the estimated population of the largest near-Earth asteroids, which are 3,300 feet across and larger. "The new data revise their total numbers from about 1,000 down to 981, of which 911 already have been found," NASA said in a statement.

NASA'S Spaceguard effort, which uses ground and space-based observations, is tracking more than 5,200 near-Earth asteroids 330 feet or larger. Astronomers believe 15,000 or more are yet to be sighted.