BEWARE OF ERRANT ASTEROIDS

On February 15 an asteroid designated 2012 DA14 will pass safely within about 17,200 miles of Earth's surface - closer than the communication satellites that will be broadcasting the news of its arrival. The asteroid is about 150 feet in diameter and has a mass estimated at about 143,000 tons.

Should an object of that size hit Earth, it would cause a blast with the energy equivalent of about 2.4 million tons - or 2.4 megatons - of TNT explosives, more than 180 times the power of the atomic blast that leveled Hiroshima.

It's almost as if nature is firing a shot across our bow to direct our attention to the vast number of nearby rocky asteroids and a few icy comets that make up what we call the near-Earth object population. We should take the warning seriously. While no known asteroids or comets represent a worrisome impact threat now, NASA's Jet Propulsion Laboratory shows more than two dozen asteroids have better than a one in a million chance of smacking into Earth within the next 100 years. That may sound reassuring, but we estimate that less than 10 percent of all near-Earth objects have been discovered. And while we are keeping a vigilant eye out for these objects in the Northern Hemisphere, we are considerably less watchful in the Southern Hemisphere.

It has been only within the last 15 years that astronomers, mostly supported by NASA, have begun discovering the vast number of near-Earth objects. Our findings have led us to the realization that Earth runs its course around the sun in a cosmic shooting gallery - with us as the target. Basketball-size rocky objects enter Earth's atmosphere daily and Volkswagen-size objects every few months, but they burn up before they hit the ground.

- THE NEWYORK TIMES