In related news, NASA has released results from its Near-Earth Orbit Wide-field Infrared Survey Explorer (NEOWISE) orbiting telescope, which included 10 new near-Earth objects that NASA believe are large enough to pose a threat. The article states:
PHAs are classified as asteroids that have a minimum orbit intersection distance of 0.05 astronomical units (1 AU is the distance from Earth to the Sun, so 0.05 AU is about 7.5 million kilometres, or 4.6 million miles).
They also must be big enough to have an absolute magnitude of 22 or brighter, which would make them bigger than 140 metres (around 500 feet) in size, assuming they were reflective enough.
So far, we know of 1,806 of these objects, and while some will give us a close shave in coming years, none seem to be destined for our backyard.