U.S. astronomers say a big asteroid is no longer even a remote threat to smash into Earth in about 20 years. 

They got a much better look at the asteroid when it whizzed by Earth on Wednesday. They recalculated, determining it was not on
path to hit Earth on April 13, 2036 as once feared.

At more than 300 metres wide, the rock could do significant damage but not cause worldwide extinctions.

About nine years ago, when astronomers first saw the asteroid, they thought there was a 2.7 per cent chance that Apophis would
smack into the planet. Later, they lowered the chances.

The asteroid is named after an evil Egyptian mythical serpent.

Donald Yeomans, who manages NASA's asteroid-tracking office, said now the asteroid will not get closer than 31,220 kilometres.

Photo: Asteroid Apophis was discovered on June 19, 2004. Image credit: UH/IA via NASA