How Many Potentially Hazardous Asteroids Are There?

According to the United States' National Aeronautics and Space Administration (NASA), there are about 4,700 potentially hazardous asteroids (PHAs), in Earth's solar system. These relatively large asteroids, also known as minor planets, might orbit close to the Earth and, in a collision, could cause major damage to the planet and its inhabitants. Although space scientists continue to look for potentially hazardous objects, including asteroids, as of 2012, only 20% to 30% of PHAs had actually been located, according to NASA.

More about asteroids:

• There is no record of a person actually being killed by an "impact event," which is the term used in the scientific community to describe a collision between space bodies.


• Potentially hazardous asteroids not only present a risk to the planet, they could also jeopardize space missions.


• The first recorded incident of a space object striking a human was in 1927. A 5-year-old Japanese girl was hit on the head by tiny stone, although she was not injured.