Near-Earth Objects: The Asteroids That Pass Close to Earth

Near-Earth Objects (NEOs) are asteroids and comets whose orbits bring them within 1.3 astronomical units of the Sun, meaning they can pass relatively close to Earth. NASA tracks over 34,000 known NEOs, with about 2,000 new discoveries each year. Of these, roughly 2,300 are classified as Potentially Hazardous Asteroids (PHAs) because they are larger than 140 meters and come within 7.5 million kilometers of Earth orbit. The Chelyabinsk meteor that exploded over Russia in 2013 was only about 20 meters across yet injured 1,500 people and damaged 7,200 buildings.

It was undetected before impact because it approached from the direction of the Sun. NASAs Planetary Defense Coordination Office coordinates detection efforts, with the upcoming NEO Surveyor space telescope expected to catalog 90% of PHAs within a decade. The DART mission successfully demonstrated asteroid deflection in 2022 by crashing into Dimorphos, a 160-meter moonlet, and changing its orbital period by 33 minutes. Future missions may use gravity tractors, nuclear devices, or kinetic impactors to deflect threatening objects..