NASA planetary defense officer Kelly Fast warns that humanity is largely defenseless against up to 15,000 undetected “city-killer” asteroids, roughly 500 feet across, which could cause regional devastation.

While large asteroids are tracked and smaller ones frequently hit Earth harmlessly, these mid-sized asteroids are difficult to detect because they orbit close to Earth and reflect little sunlight.

To address this, scientists plan to launch the Near-Earth Object Surveyor telescope next year, using thermal imaging to spot previously hidden space rocks.

Even if detected, current defense capabilities are limited: the 2022 DART mission demonstrated that asteroid deflection is possible, but there are no ready-to-launch systems for mid-sized threats, the New York Post has reported.

Experts caution that funding and preparedness are lacking, and some asteroids, like YR4, may even pose future lunar collision risks, prompting extreme mitigation proposals such as nuclear disruption.