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Q. Could a killer asteroid hit Earth? — Lenora A.
A. Yes, but it's really not likely to happen anytime soon.
Astronomers have calculated that there may be more than a thousand asteroids of one kilometer (0.6 miles) diameter and larger near Earth's path around the Sun. That size would be big enough to devastate our planet.

NASA is compiling a census of the so-called NEOs — Near Earth Objects — which should be completed by 2008. Already, hundreds have been identified.

Why is it important? Scientists have suggested that one big boulder from space may have struck Earth 65 million years ago, changing the global climate and bringing about the extinction of millions of dinosaurs that had roamed Earth.

Fortunately for Earth's current residents, collisions with asteroids are rare. Scientists figure really big crashes of those one-kilometer or larger rocks take place only about once every million years.

Smaller asteroids smash into Earth every few centuries, mostly splashing into the oceans. However, if even a small one were to hit near a populated area, it could touch of a large regional disaster.

Could one hit before we knew it? There wouldn't seem to be any way for a killer asteroid to crash into Earth without at least a minimal warning period. Around the world, professional and amateur astronomers are on the lookout for NEOs. Many are so keenly interested they constantly access data calculations from observations of the skies.

Learn more:

• About asteroids STO  »»
• Near Earth Object Program NASA  »»

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