NASA says it has found more than 90 percent of the biggest asteroids that might pose a threat to Earth.
These are asteroids that are 3,300 feet wide or larger. The space agency said its sky-mapping spacecraft called WISE has discovered 911 of the 981 largest asteroids predicted by models.
Scientists say they now think there are fewer medium-sized asteroids than originally thought. They now estimate there are about 19,500 asteroids between 330 feet and 3,300 feet wide, down from 35,000.
WISE was launched in 2009 to map the whole sky in search of hidden asteroids, comets and other celestial objects. The mission is managed by the NASA Jet Propulsion Laboratory in California.