Why can some near-Earth asteroids pose an impact hazard to Earth?

Near-Earth asteroids pose an impact hazard primarily because their orbits around the Sun cross or closely approach the orbit of Earth. These objects, categorized as near-Earth objects (NEOs), can have their paths altered over time, potentially leading to a collision with the planet.123

The severity of such an impact is determined by the object's mass and relative velocity, which together dictate the total kinetic energy released upon impact. While smaller objects may break up in the atmosphere, larger bodies—such as those exceeding 1 km in diameter—can cause catastrophic global consequences, including climate disturbances or mass extinctions.312

To manage this risk, scientists identify and monitor potentially hazardous asteroids (PHAs) to refine their orbital predictions. The Torino Impact Hazard Scale is used to communicate the level of public concern based on an object's collision probability and estimated energy. Protecting the planet from such events is a critical scientific and ethical priority, as early detection is essential to potentially averting a catastrophe.412