The risk of an impact from an asteroid or comet increases in proportion to its size. Most objects entering Earth's atmosphere would disintegrate before reaching the surface, causing particles to fall in seconds to the ground. Objects tens of meters in diameter or the size of a large house would cause severe local damage, but would not cause a global threat. It would take an object 1-2 km in diameter (more than 1 mile) to cause a global threat.Many scientists believe that an asteroid 10 km in diameter was responsible for the extinction of the dinosaur.

The impact of an object weighing several tens of billions of tons would likely cause a ground explosion comparable to one million megatons of TNT. The destruction of the Earth would be blown into the stratosphere, encircling the Earth and blocking out the Sun. The effect would be perpetual winter, which would prevent plants from growing. The ozone would be destroyed creating a greenhouse effect. If there were early warnings of several years, it might be possible to launch rockets to explode the objects before they entered Earth's atmosphere; without exploding, there would be no option but to evacuate.

QUESTIONS - BACK

Please send any comments to:
Curator: Tom.Benson@grc.nasa.gov
Responsible Official: Kathy.Zona@grc.nasa.gov