The Earth survived a close call with a 143,000-tonne asteroid Friday as it whizzed by our planet at a distance closer than any other cosmic rock its size.
Asteroid 2012 DA14, as labelled by NASA, came within 27,600 kilometres, closer than some satellites orbiting the Earth.
The asteroid is only about 50 metres wide, but scientists said it could have done 鈥渋mmense鈥� damage if it ever struck our planet because of its weight.
By comparison, the asteroid that struck Earth 65 million years ago and is believed to have wiped out dinosaurs was nearly 10 kilometres across.
Astronomers watched DA14 pass us by over the Indian Ocean at about 2:25 p.m. Eastern time. It was very difficult to see the rock with a naked eye, but residents of some parts of Asia, Australia and eastern Europe were able to catch a flash of light with telescopes and binoculars.
NASA said the close encounter was not related to another spectacular cosmic event on Friday 鈥� a meteor explosion above Russia鈥檚 Ural Mountains.
NASA estimates that the meteor was about 15 metres wide and weighed 7,000 tonnes before it burst into the atmosphere. The explosion injured an estimated 1,000 people, shattered windows and caused panic among the residents of Russia鈥檚 Chelyabinsk region.
Experiencing a meteor explosion and a close asteroid sighting is 鈥渧ery rare and historic,鈥� said Jim Green, NASA's director of planetary science.
"These fireballs happen about once a day or so, but we just don't see them because many of them fall over the ocean or in remote areas. This one was an exception."
As for the asteroid, NASA estimates that an object of that size makes a close approach every 40 years. The likelihood of it striking the Earth is every 1,200 years.
The chances of us getting hit by a large asteroid without warning are 鈥渆xtremely low, so low that it鈥檚 ridiculous,鈥� said former Apollo astronaut Rusty Schweickart, who is now the chairperson emeritus of the B612 Foundation monitoring dangerous asteroids.
鈥淏ut the smaller ones are quite different," Schweickart said. "If we get hit by one of them, it's most likely we wouldn't have known anything about it before it hit."
A spacecraft could theoretically be launched in an effort to change the direction and speed of an asteroid that鈥檚 on a collision course with Earth.
But scientists would need to know up to 30 years in advance of a large asteroid鈥檚 approach to successfully deflect it, Schweickart said.
Experts say there could be anywhere between 500,000 and one million 鈥渘ear-Earth鈥� asteroids in space, but less than one per cent have been spotted. Only 9,600 asteroids have been catalogued by astronomers.
NASA says the Earth鈥檚 atmosphere gets hit with 100 tonnes of 鈥渟pace junk鈥� every day. Most of it is tiny and burns up before reaching the ground.
With files from The Associated Press
