Planetary defense exercise uses asteroid Apophis as hazardous asteroid stand-in

Watching the skies for large asteroids that could pose a hazard to Earth is a global endeavor. So, to test their operational readiness, the international planetary defense community will sometimes use a real asteroid's close approach as a mock encounter with a "new" potentially hazardous asteroid. The lessons learned could limit, or even prevent, global devastation should the scenario play out for real in the future.