Big asteroid no longer a threat to Earth

WASHINGTON (AP) - Upon further review, a big scary-sounding asteroid is no longer even a remote threat to smash into Earth in about 20 years, NASA says.

Astronomers got a much better look at the asteroid when it whizzed by Earth on Wednesday. They recalculated the space rock's trajectory and determined it was not on a path to hit Earth on April 13, 2036 as once feared possible.

At more than 323 metres wide, the rock called Apophis could do significant damage to a local area if it hit and perhaps even cause a tsunami. But it was not large enough to trigger worldwide extinctions. One prominent theory that explains the extinctions of dinosaurs and other species 65 million years ago says a 9.6km-wide meteorite hit Earth and spewed vast amounts of dust into the air, cooling and darkening the planet.

About nine years ago, when astronomers first saw Apophis, they thought there was a 2.7 per cent chance that it would smack into our planet. Later, they lowered the chances to an even more unlikely 1 in 250,000.

Now it's never mind.

"Certainly 2036 is ruled out," said Mr Donald Yeomans, manager of NASA's Near Earth Object Programme. "It's why we track them so we can be assured that they won't get dangerously close."

He said now the asteroid, named after an evil Egyptian mythical serpent, would not get closer than 31,200 km. That's still the closest approach asteroid watchers have seen for a rock this large. And when astronomers got a closer look, they noticed it was about 54 metres larger than they thought, but not a threat.

Asteroids circle the sun as leftovers of failed attempts to form planets billions of years ago. When asteroids enter Earth's atmosphere, they become meteors and when they hit the ground they are meteorites.

This is the second time in as many months the asteroid watchers have had good news for Earth. Last month, astronomers got a closer look at a smaller asteroid that they had previously calculated had a 1 in 500 chance of hitting Earth, this time in 2040. And they decided the 140-m asteroid was no longer a threat.

If you still want to see a space rock come cosmically close to Earth, there's always next month.

On Feb 15, a small asteroid, only 40m-wide, will come close to Earth, about 27,350 km above the equator. That's so close it will come between our planet and some of the more distant satellites that circle the globe. But it will miss Earth.

"This will be the closest passage of an object this size," Mr Yeomans said.

That asteroid, called 2012 DA14, should be visible with smaller telescopes and binoculars, but mostly in Eastern Europe, Asia and Australia, he said.