Search for Asteroid Threats

What is the true long-term threat of Near Earth Objects? NASA defines “potentially hazardous” as a Near Earth Object that will pass within .05 AU from Earth and is at least 140 meters in diameter. (

But consider the damage left by a 30-meter object in the famed Siberian impact of 1908:

“Recent scientific studies by meteorite researcher Christopher Chyba have estimated that the Tunguska event may have been caused by the explosion of a stony meteroid about 30 meters in diameter traveling at about 15 km/s. Compare the energy released by such an object with that of an atomic bomb such as those dropped on Japan in World War II.”

The truth is no one really knows how many asteroids this size or larger are out there. According to NASA sources, the population breaks down as follows:

100 meters in diameter: 300,000
500 meters in diameter: 10,000
Over one kilometer in diameter: 500-1,000

The good news is that eight projects are at work to search for them, including NASA’s NEO-Wise space telescope, and more are coming on line soon. The bad news is that fewer than 8,000 of these have been discovered so far.

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