A mystery space object, believed to be an asteroid, is set to pass close by the earth, Nasa has said, as astronomers attempt determine its origins.
The object, called 2010 AL30, is set to pass within 122,000km of the Earth, or just a third of the distance out to the moon, around lunchtime on Wednesday.
Its discovery earlier this week has baffled scientists, with some astronomers speculating it may be space junk given its width is similar to a man-made object.
Nasa said it was more likely to be a tiny asteroid, one of approximately 2 million such objects in near-Earth space.
Measuring between 10 to 15 metres wide, experts say it is too small to cause any damage to the earth.
The object, which will pass the earth at 1247 GMT, was discovered by, NASA-funded Lincoln Near-Earth Asteroid Research programme on Monday and pictured by the Australian Skylive-Grove Creek Observatory in Trunkey Creek, New South Wales.
Experts say professional astronomers will be able to see it shining with a brightness of a 14th-magnitude star similar to that of Pluto in the constellations of Orion, Taurus, and Pisces.
Italian scientists Ernesto Guido and Giovanni Sostero, from the Remanzacco Observatory, told Ria Novosti, the Russian News Agency, that it had an orbital period of almost exactly one year and might be a man-made object such as a spent rocket booster.
A Nasa spokesman said the asteroid did not pose a risk with stony asteroids under 25 meters in diameter more likely to “burn up in our atmosphere, causing little or no ground damage”.
He also dismissed claims it was a man-mad object.
“Because its orbital period is nearly identical to the Earth's one year period, some have suggested it may be a manmade rocket stage in orbit about the sun,” he said.
“However, this object's orbit reaches the orbit of Venus at its closest point to the sun and nearly out to the orbit of Mars at its furthest point, crossing the Earth's orbit at a very steep angle. This makes it very unlikely that 2010 AL30 is a rocket stage.
“Furthermore, trajectory extrapolations show that this object cannot be associated with any recent launch and it has not made any close approaches to the Earth since well before the Space Age began.”