An edge-on view of our solar system with the dots representing a snapshot of NEAs (blue) and PHAs (orange) on a typical day (Image: NASA/JPL-Caltech)
Diagram showing the differences between orbits of a typical near-Earth asteroid (blue) and a potentially hazardous asteroid, or PHA (orange) (Image: NASA/JPL-Caltech)
Potentially hazardous asteroids (PHAs) are a subset of near-Earth asteroids (NEAs) that have the potential to come within five million miles (eight million kilometers) of Earth, and are of a size large enough to make it through Earth’s atmosphere to cause significant damage on a regional, or greater, scale. NASA’s asteroid-hunting NEOWISE mission has now provided the best estimate yet of the number of PHAs in our solar system, along with their origins and the potential dangers they might pose.
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