Death from above: 4,700 asteroids pose risk for Earth

AsteroidJust when we thought we had escaped Armageddon, this: NASA announced late Wednesday that approximately 4,700 potentially hazardous asteroids (PHAs) are currently buzzing around “near” Earth. The estimate — which could be off by as many as 1,500 PHAs — is based on analysis of new information gathered by NASA’s Wide-field Infrared Survey Explorer (WISE) telescope.

NASA defines PHAs as any asteroid within 5 million miles of Earth that has a diameter greater than 330 feet (or 100 meters). At that size, the asteroid would be large enough to survive the plunge through Earth’s atmosphere, thus allowing them to wreak havoc on humanity.

The updated PHA estimate comes as a result of the a WISE mission called “NEOWISE.” As part of NEOWISE, NASA scientists sampled 107 PHAs to come up with their 4,700 PHA figure, as well as other predictions about the population of PHAs in general. Only about 20 to 30 percent of the PHAs have yet been detected.

“The NEOWISE analysis shows us we’ve made a good start at finding those objects that truly represent an impact hazard to Earth,” said Lindley Johnson, program executive for the Near-Earth Object Observation Program, in a statement. “But we’ve many more to find, and it will take a concerted effort during the next couple of decades to find all of them that could do serious damage or be a mission destination in the future.”

Of those PHAs discovered, many of those closest to our planet shine more brightly than asteroids that often stray farther away from Earth. The researchers say that their brightness is likely because they are made of either rock, like granite, or some type of metal. The composition of the PHAs matters, as it helps the researchers determine how well they would survive a trip through our atmosphere. NASA says that the PHAs that are closer to Earth may one day be available for human or robotic missions.

NASA says that an asteroid that measures 40 meters in diameter would strike Earth with the same force as a 3-megaton nuclear bomb.

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