Observations from NASA's Wide-field Infrared Survey Explorer (WISE) have led to the best assessment yet of our solar system's population of potentially hazardous asteroids. The results reveal new information about their total numbers, origins and the possible dangers they may pose. Potentially Hazardous Asteroids, or PHAs, have the closest orbits to Earth's, coming within five million miles, and they are big enough to survive passing through Earth's atmosphere and cause damage on a regional, or greater, scale.