Mainzer said between 20% and 30% of the estimated 4, 700 potentially hazardous objects have been discovered so far.

CNN: NASA estimates 4,700 'potentially hazardous' asteroids

More than 1, 300 near-Earth objects have been classified as potentially hazardous to Earth, meaning that someday they may come close or hit our home planet.

CNN: While you were working: An asteroid just flew by