for National Geographic News
A hundred years after a mysterious and massive explosion struck Russia, experts are warning that Earth is ill prepared to face a cosmic catastrophe that could do similar damage.
The blast, known as the Tunguska event, leveled some 770 square miles (2,000 square kilometers) of forest with the power of nearly 200 Hiroshima-size atomic bombs.
Remarkably few people witnessed the event, and debate has raged for decades about its cause.
One of the leading theories is that a comet or asteroid hit Earth or exploded upon entering the atmosphere above remote western Siberia.
"Had that same object exploded over a metropolitan area, there would have been millions of people killed," U.S. Representative Dana Rohrabacher (a Republican from California) said yesterday at a briefing at the Planetary Society in Pasadena, California.
"Right now we have no plan in place to detect these objects far enough out to deflect them."
Odds Are Slim
Meteors in the form of about a hundred tons of dusty particles reach Earth every day.
In fact meteors seen on an average night or during an annual shower are mostly small particles burning up as they enter our atmosphere.
Because Earth is pelted with tiny objects all the time, assessing the probability of larger impacts is far more difficult and controversial.
Experts admit they don't yet know how many so-called Near-Earth Objects (NEOs) orbit close enough to pose a threat.
Most NEOs are asteroids, and NASA currently classifies about 959 asteroids as potentially hazardous.
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