Near miss, but we're not out of the woods

Last week, a large space rock numbered 2012 DA14 missed Earth, but now is not the time for a sigh of relief because there are still thousands of potentially hazardous asteroids in space.

"Scientists have discovered 1,379 potentially hazardous asteroids, and even more than that number of PHAs have yet to be found," said Zhao Haibin, an asteroid researcher at Purple Mountain Observatory under the Chinese Academy of Sciences.

Asteroids with a diameter of at least 100 meters closer than 7.5 million kilometers to Earth, are considered, "potentially hazardous".

Apophis, with a diameter of 300 meters, is one of the most talked-about near-Earth asteroids. It caused great concern in 2004 when initial observations indicated a 1-in-29 chance it would strike Earth in 2029.

Although further observation dismissed the possibility of an impact with Earth or the moon in 2029, it has a 4-in-1 million chance of hitting Earth in 2036.

"If an asteroid of this size hit the continent, it would destroy an area equal to half of China. If it hit the ocean, it would cause a tsunami that would affect all coastal cities," Zhao said.

Internationally, plans to prevent asteroid collisions are still in the research stage, Zhao said.

"One way is to detonate a missile on the asteroid so its orbit would be slightly altered to miss Earth. Another option is to slowly change its orbit, for example by attaching a sail to the asteroid.

"But these plans have gone largely unpracticed," he said.

chengyingqi@chinadaily.com.cn

(China Daily 02/22/2013 page5)