NASA-JPL: Potentially Hazardous Asteroids

Astrogeology, Asteroids, Robots, Space Flight & Extraterrestrial Matters

Date posted: 08/13/09

PHA's are currently defined based on parameters that measure the asteroid's potential to make threatening, close approaches to the Earth. Specifically, all asteroids with an 0.05 AU or less and an absolute magnitude of 22.0 or less are considered PHAs.