A small asteroid will pass closer to Earth next week than the TV satellites that ring the planet, but there is no chance of an impact, NASA said last night.
The celestial visitor, known as 2012 DA14, was discovered last year by a group of amateur astronomers in Spain.
The asteroid is about the size of an Olympic swimming pool at 46m in diameter and is projected to come as close as 27,520km from Earth during its 15 February approach.
That would make it the closest encounter since scientists began routinely monitoring asteroids about 15 years ago.
Television, weather and communications satellites fly about 800km higher. The moon is 14 times farther away.
Even so, "no Earth impact is possible," astronomer Donald Yeomans, with NASA's Jet Propulsion Laboratory in Pasadena, California, told reporters during a conference call.
The time of the asteroid's closest approach will be 7.24pm Irish time.
It will be daylight in the United States, but dark in eastern Europe, Asia and Australia, where professional and amateur astronomers will be standing by with telescopes and binoculars to catch a view.
DA14 will soar through the sky at about 13km per second. At that speed, an object of similar size on a collision course with Earth would strike with the force of about 2.4 million tonnes of dynamite.
The last time that happened was in 1908 when an asteroid or comet exploded over Siberia, levelling 80 million trees over 2,150 sq/km.
"Although they wouldn't [cause] a global catastrophe if they impact the Earth, they still do a lot of regional destruction," said Lindley Johnson, who oversees the Near-Earth Object Observations Program at NASA headquarters in Washington DC.
NASA has been on a mission to find and track all near-Earth objects that are 1km in diameter or larger.
The effort is intended to give scientists and engineers as much time as possible to learn if an asteroid or comet is on a collision course with Earth, in hopes sending up a spacecraft or taking other measures to avert catastrophe.
About 66 million years ago, a 10km object smashed into what is now the Yucatan Peninsula in Mexico leading to the demise of the dinosaurs as well as most plant and animal life on Earth.
The planet is regularly pelted with objects from space, adding up to about 100 tonnes of material per day, Mr Yeomans said.
"Basketball-sized objects come in daily. Volkswagen-sized objects come in every couple of weeks. As you get to larger and larger sizes the number of objects out there is less and less, so the frequency of hits goes down," Mr Yeomans said.
Something the size of DA14 can be expected to strike Earth about every 1,200 years.
"For objects of this size, this is the closest predicted encounter that we're aware of," Mr Yeomans said.