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Why can near-Earth asteroids pose an impact hazard to Earth?
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Small body
Asteroid Ida and its satellite, Dactyl, photographed by the Galileo spacecraft on August 28, 1993, from a distance of about 10,870 km (6,750 miles). Ida is about 56 km (35 miles) long and shows the irregular shape and impact craters characteristic of many asteroids. The Galileo image revealed that Ida is accompanied by a tiny companion about 1.5 km (1 mile) wide, the first proof that some asteroids have natural satellites.
Near-Earth asteroids (NEAs) pose an impact hazard to Earth primarily because their orbits cross or closely approach the path of our planet around the Sun.12
These objects, particularly those classified as Apollo or Aten asteroids, move through the inner solar system and can be gravitationally perturbed, leading to potential collisions. The hazard is significant due to the immense kinetic energy released during such an event. For example:123
- Local Destruction: Objects roughly 50–100 meters in diameter can cause significant localized damage, similar to historical events like the Tunguska explosion.4
- Global Catastrophe: Larger asteroids, such as those 1 km or more in diameter, could trigger global climate disturbances or massive tidal waves. An impact from an object approximately 10 km across is widely believed to have caused the mass extinction of the dinosaurs.134
Because these impacts pose a fundamental threat to human life and the environment, astronomers actively track potentially hazardous asteroids to assess collision probabilities and develop strategies for planetary defense.154