Pasadena's Nasa Jet Propulsion Laboratory said Thursday it has pinpointed 90 percent of the asteroids that could pose a threat to Earth.
The mission, managed by JPL, says all of the mapped asteroids are 3,300 feet wide or larger. The asteroids were mapped by a spacecraft called WISE that so far has discovered 911 of the 981 largest threats predicted by models.
"NEOWISE allowed us to take a look at a more representative slice of the near-Earth asteroid numbers and make better estimates about the whole population," Amy Mainzer, the lead author of the new study and principal investigator for the NEOWISE project, told NASA.
"It's like a population census, where you poll a small group of people to draw conclusions about the entire country," she said.
Scientists say they now think there are fewer medium-sized asteroids than originally thought. They estimate there are about 19,500 asteroids between 330 feet and 3,300 feet wide, down from 35,000.
Tim Spahr, the director of the Minor Planet Center at the Harvard Smithsonian Center for Astrophysics, told NASA that the findings greatly improve the chance earthlings will be caught off guard.
"The risk of a really large asteroid impacting the Earth before we could find and warn of it has been substantially reduced," Spahr said.
WISE was launched in 2009 to map the whole sky in search of hidden asteroids, comets and other celestial objects.
KPCC's Lily Mihalik contributed to this report.