一颗约喷气式飞机大小的小行星，将会在下周与我们近距离擦肩而过。 请看CBC有关报道

 

http://www.cbc.ca/news/world/story/2013/02/07/technology-asteroid-flyby.html

 

Jet-sized asteroid to pass between Earth and satellites

 

But no risk that it will hit us

 

A space rock about the size of a jet plane will zip so close to Earth that it will briefly come between us and our weather satellites next week.

Asteroid 2012 DA14 will be just 27,700 kilometres from the surface — a mere tenth of the distance between the Earth and the moon — when it makes its closest approach around 2:24 p.m. ET on Feb. 15. At that time, it will be zooming by at about 28,100 kilometres per hour or 7.82 kilometres per second relative to Earth.

DA14 will come 8,100 kilometres closer to Earth than man-made weather and communications satellites that are in geosynchronous orbit, which means they circle the Earth once a day.

In fact, the 45-metre diameter, 130,000-tonne asteroid will come closer than any object its size has ever been predicted to come before.

The asteroid's orbit is so well known that "there's no chance of a collision," said Donald Yeomans, manager of NASA's Near Earth Object Office, at a news conference Thursday.

Nor is it likely to hit any satellites, as it's too close to Earth to hit the geosynchronous satellites, but a lot further out than the bulk of satellites orbiting, including the International Space Station, located 386 kilometres above the surface.

"This asteroid seems to be passing the sweet spot between the GPS satellites and weather and communications satellites," Yeomans said.

He added that just to be safe, the U.S. space agency is giving satellite providers detailed information about the asteroid's position at different times so they can compare that to the position of their satellites.

Less frequent visits expected

While DA14 has been coming relatively close to Earth about twice a year, that's about to change, Yeomans said. As it flies by, the Earth's gravity will actually perturb the asteroid's orbit, shaving a couple of months off its usual 12-month travel time around the sun.

"It won't come back in the Earth's neighbourhood anywhere near as frequently as it has in the past," he said. "The Earth is going to put this one in an orbit that is considerably safer than the orbit it has been in."

NASA estimates that asteroids the size of DA14 actually fly this close about once every 40 years and hit the Earth roughly once every 1,200 years. The last time it happened was on June 30, 1908, when a meteorite crashed in Tunguska, Russia, and levelled trees over 2,200 square kilometres.

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