Analyzing data from the agency's Wide-field Infrared Survey Explorer, astronomers estimate there are roughly 19,500 -- not 35,000 -- mid-size near-Earth asteroids, a NASA release said Thursday.
The NEOWISE survey project, the most accurate census to date of near-Earth asteroids that orbit within 120 million of the sun into Earth's orbital vicinity, scanned the entire celestial sky twice in infrared light between January 2010 and February 2011.
"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 of NASA's Jet Propulsion Laboratory in Pasadena, Calif., said. "It's like a population census, where you poll a small group of people to draw conclusions about the entire country."
Scientists say the improved understanding asteroid numbers may indicate the hazard to Earth of a collision could be somewhat less than previously thought.