Belfast Telegraph

Sunday 20 April 2014

Asteroid passes Earth in fly-by

A simulation of asteroid 2012 DA14 approaching from the south as it passes through the Earth-moon system (AP/NASA/JPL-Caltech)

An asteroid has come within an incredible 17,150 miles of the Earth - making the closest known flyby for a rock of its size.

In a chilling coincidence, a meteor exploded above Russia's Ural Mountains just hours before the asteroid zoomed past the planet.

Scientists across the world, along with Nasa, insisted the meteor had nothing to do with the asteroid since they appeared to be travelling in opposite directions. The asteroid is a much more immense object and delighted astronomers in Australia and elsewhere who watched it zip harmlessly through a clear night sky.

"It's on its way out," reported Paul Chodas of Nasa's Near-Earth Object program at Jet Propulsion Laboratory in California.

Asteroid 2012 DA14, as it is called, came closer to Earth than many communication and weather satellites orbiting 22,300 miles up. Scientists insisted these, too, would be spared, and they were right.

The asteroid was too small to see with the naked eye even at its closest approach around 8.25pm GMT over the Indian Ocean near Sumatra. The best viewing locations, with binoculars and telescopes, were in Asia, Australia and eastern Europe. Even there, all anyone could see was a pinpoint of light as the asteroid buzzed by at 17,400 mph.

As asteroids go, this one is a shrimp. The one that wiped out the dinosaurs 65 million years ago was six miles across. But this rock could still do immense damage if it ever struck given its 143,000-tonne heft, releasing the energy equivalent of 2.4 million tonnes of TNT and wiping out 750 square miles. By comparison, NASA estimated that the meteor that exploded over Russia was much smaller - about 49ft wide and 7,000 tonnes before it hit the atmosphere, or one-third the size of the passing asteroid.

As for the back-to-back events, "this is indeed very rare and it is historic," 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 the countdown for the asteroid's close approach entered the final hours, Nasa noted that the path of the meteor appeared to be quite different than that of the asteroid, making the two objects "completely unrelated." The meteor seemed to be travelling from north to south, while the asteroid passed from south to north - in the opposite direction.

Most of the solar system's asteroids are situated in a belt between the orbits of Mars and Jupiter, and remain stable there for billions of years. Some occasionally pop out, though, into Earth's neighbourhood.

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