A Halloween asteroid the size of four football pitches is due to fly past Earth today.
The massive space rock, affectionately called the “Great Pumpkin” by astronomers, is expected to miss the planet by just 483,000km.
But scientists have insisted there is no need to be scared, as the asteroid will remain further away than the moon.
Dr Detlef Koschny, of the European Space Agency (ESA), said: "The fact that such a large near-Earth object capable of doing significant damage if it were to strike our planet was discovered only 21 days before closest approach demonstrates the necessity for keeping daily watch of the night sky."
There is no chance of the asteroid hitting the Earth for the next 100 years at least, and it is not included in the agency’s official list of potentially threatening NEOs (near-Earth objects).
The 400 metre-wide asteroid, given the official designation TB145, was spotted by astronomers in Hawaii on October 10th.
It is due to fly past the Earth at about 5pm, Irish time.
Very little is known about the object, other than what scientists have been able to infer from observations made so far.
‘Large uncertainty’
Dr Marco Micheli, an astronomer from ESA's NEO Coordination Centre in Italy, said: "The diameter of about 400 metres has a large uncertainty, as is usual in cases of any object for which we do not yet know details, such as its composition."
Scientists estimate that there are about 5,000 NEOs of similar size hurtling through Earth’s region of the solar system, of which a significant number have not yet been discovered.
To watch out for them, ESA is developing automated “fly-eye” telescope technology which should be ready for testing at the end of next year.
“Objects of this size are often spotted by automated surveys,” said Dr Koschny.
“The only difference is that, being so large, they are often found when they are quite far away, out to 2.5 times the sun-Earth distance, and not just before a close approach, as in this case.”
PA