What would happen if an asteroid hit Earth today?

The answer

The impact depends dramatically on size. An asteroid 25 meters across (like the 2013 Chelyabinsk meteor) would explode in the atmosphere with the force of 500 kilotons of TNT, shattering windows for miles. A 1-kilometer asteroid would cause global devastation: firestorms, tsunamis, and enough dust to block sunlight for months, triggering crop failure worldwide. A 10-kilometer impactor (like the one that killed the dinosaurs) would cause a mass extinction. NASA's DART mission in 2022 successfully demonstrated that we can deflect an asteroid by crashing a spacecraft into it.