Christmas Eve asteroid to whizz harmlessly past the Earth

After a comet for Halloween, another Earthly holiday will be marked by a visit from a celestial body -- this time a large asteroid zipping past on Christmas Eve, astronomers said Thursday.

The massive space rock, about two kilometres (1.2 miles) in length, will cruise by our planet about 28 times farther than the distance between Earth and the Moon, Mark Bailey, director of the Armagh Observatory in Northern Ireland, told AFP.

"It's not what you would call an Earth-grazer or anything like that," he said -- contradicting media reports that it could pass near enough to trigger earthquakes and volcanoes.

"It's at a distance such that you could expect several such encounters with objects of that sort of size every year -- so maybe every couple of months you would get one coming that close, and of the same size."

The asteroid, dubbed 163899 or 2003 SD220, will pass at a distance of some 11 million kilometres.

The year 2015 had already seen several flit by much closer than that.

The objects that truly concern astronomers, are those that get closer to Earth than the Moon -- out there at a distance of more than 300,000 km.

Once every 100,000 years does it happen that a space rock larger than a kilometre collides with our planet, said Bailey.

"Asteroids of that size are interesting -- it's about the kilometre or half-kilometre size range that, it doesn't matter where on Earth it hits, has a globally devastating impact on the environment."

Maria-Antonietta Barucci, an astronomer at the Paris Observatory, affirmed the asteroid was "not on our list of dangerous objects".

"We can all be calm, relaxed, and enjoy Christmas," she said.

The next truly "close encounter" will be with the asteroid Apophis, a few hundred metres wide, which is expected to shave past Earth at about a tenth of the Earth-Moon distance on April 13, 2029, said Bailey.

Apophis will be visible with the naked eye as a faint moving point of light in the sky, but again, won't risk colliding with Earth.

"Apophis is a really unusual encounter, approaching the Earth around 400 times closer than 163899," said Bailey.

A comet with an eery skull-like face passed by earth on October 21, at some 486,000 kilometres.