You can sleep easy tonight. Or easy-ish. NASA today announced that it has identified more than 90% of the giant asteroids out there that could threaten Earth (think dinosaur-killing size). "We know now where most of them are and where most of them are going. That really has reduced our risk" of an impact, says a NASA scientist. And as for mid-sized asteroids—those capable of demolishing a metropolitan city—NASA has reduced its estimate of the number in existence by 44%. But it hasn't tracked many of them down yet. "Fewer does not mean none. There are still tens of thousands out there that are left to find."
NASA's updated data comes compliments of the Wide-field Infrared Survey Explorer, or WISE, which launched in 2009 to seek out near-Earth objects. For the largest asteroids—bigger than 3,300 feet across—NASA said 911 of the 981 thought to exist have been found, and none are poised to threaten the planet in the near future. As for the mid-size ones, it believes about 19,500 asteroids between 330 and 3,300 feet wide exist, reports the AP. About 5,200 of those have been IDed. WISE is not equipped to detect the more than a million smallest asteroids that could cause damage if they impact Earth. (Read more NASA stories.)