NASA's biggest asteroid threat: The asteroids NASA can’t see and why they’re the ones that worry scientists most

NASA's top planetary defense expert reveals the biggest threat isn't Hollywood-style doomsday rocks, but undiscovered 'city-killer' asteroids. While large and small threats are known, an estimated 25,000 mid-sized objects remain unfound, posing a significant regional danger. Despite a successful deflection test, Earth currently lacks an immediate defense system.