Nasa survey 4,700 potentially hazardous asteroids, plus or minus 1,500 space rocks


A new NASA survey has pinned down the number of asteroids that could pose a collision threat to Earth in what scientists say is the best estimate yet of the potentially dangerous space rocks.

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The survey found there are likely 4,700 potentially hazardous asteroids, plus or minus 1,500 space rocks, that are larger than 330 feet (100 meters) wide and in orbits that occasionally bring them close enough to Earth to pose a concern, researchers said. To date, only about 30 percent of those objects have actually been found, they added.

Potentially hazardous asteroids, or PHAs in NASA-speak, are space rocks in orbits that come within 5 million miles (8 million kilometers) of Earth and are large enough to cause damage on regional or global scale if they were ever to hit our planet.

The new study was based on observations from NASA’s Wide-field Infrared Survey Explorer (WISE), an infrared space telescope. While the telescope data returned an estimate of the potentially dangerous near-Earth asteroid population that is similar to previous projections, it also revealed some surprising new results.

According to the survey, about twice as many asteroids are in so-called “lower-inclination orbits” — which are more closely aligned with Earth’s path around the sun than other objects — than previously thought researchers said. [Video: WISE Telescope’s Asteroid Census]

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