How big is the asteroid threat, really?

NASA will try out planetary defense technology with its Double Asteroid Redirection Test (DART) this month, but don't worry — it's not because a space rock is just about to hit us.

How big is the asteroid threat, really?
NASA will try out planetary defense technology with its Double Asteroid Redirection Test (DART) this month, but don't worry — it's not because a space rock is just about to hit us.