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Published: Thursday, 10/6/2011

Rest easy

No one has to worry that the Earth has a giant bull's eye painted on it. According to the Wide-field Infrared Survey Explorer, a telescope satellite launched by NASA in 2009, humans don't have to lose sleep -- at least for a few centuries -- over giant asteroids on a collision course with their planet.

WISE's infrared-light survey of near-Earth asteroids catalogued galaxies, stars, comets, asteroids, and the 100,000 objects in the asteroid belt between Mars and Jupiter. Scientists now believe that only 981 of the near-Earth objects out there are big enough to end life on this planet. Those asteroids have a diameter between 3,300 feet and several miles.

For some perspective, the killer asteroid that ended the reign of the dinosaurs some 65 million years ago was roughly 6 miles in diameter. WISE has accounted for at least 911 of these monsters. Prospects for detecting the others is rated as excellent. But, again, none is speeding this way.

WISE also sniffed out 19,500 medium-size asteroids -- between 300 feet and 3,000 feet wide -- that pose a lesser threat, but still are capable of taking out a large city. None of them is on a trajectory with the planet either.

After mapping the positions of 93 percent of all near-Earth asteroids, WISE also has established a census for Earth's corner of the cosmos that cuts the number of medium-size asteroids by 44 percent. That's a second piece of really good news from WISE's mission.

Until 100 percent of the sky is mapped by WISE and other technology, NASA won't be able to say definitively that every potential havoc-causing asteroid has been accounted for.

Still, humans know a lot more about the trajectory of asteroids than they did two years ago. And we can rest easy that there are few of them that might threaten the Earth.

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