Fears that a giant asteroid could wack into the planet on March 21 2014 and plunge it into a nuclear winter are misplaced, they said, explaining that fresh calculations showed the monster rock would safely pass us by.

The asteroid, known as 2003 QQ47, was first spotted on August 24, and NASA's Jet Propulsion Laboratory (JPL), making a preliminary estimate of its orbit, said there was a tiny chance -- one in only 909,000 -- that it would collide with Earth.

Around 1.2 kilometers (two-thirds of a mile) across, and hurtling through space at 120,000 kilometers (75,000 miles) per hour, 2003 QQ47 would unleash energy equivalent to 350,000 megatonnes of TNT, or eight million times the power of the Hiroshima bomb.

2003 QQ47 was initially graded the lowest step on the Torino scale, which rates the chances of newly discovered asteroids and comets hitting the Earth.

This grading means the asteroid is not a significant risk but "merits special monitoring."

But asteroid experts, in a circular distributed among their community on Wednesday and received by AFP, have now downgraded that risk and accused the media of hyping the scare.

NASA specialist Ron Baalke said that the agency's Lincoln Near Asteroid Research (LINEAR) telescope in New Mexico was tasked on Tuesday to make further observations of 2003 QQ47.

"We've just computed a new orbit solution, and 2003 QQ47 has dropped to Torino [zero]," Baalke announced. "(...) The 2014 potential impact has been eliminated."

The asteroid is around one-tenth of the size of the rock that is believed to have wiped out dinosaurs on Earth 65 million years ago.

Asteroids such as 2003 QQ47 are chunks of rock left over from the formation of the Solar System 4.5 billion years ago.

Most are kept at a safe distance from Earth in the asteroid belt between the orbits of Mars and Jupiter.

But the gravitational influence of giant planets such as Jupiter can nudge asteroids out of these safe orbits and send them plunging into the Earth's neighbourhood.

SPACE.WIRE