WASHINGTON — Hold on to your hats: an asteroid will zoom within spitting distance of Earth next week, in what Nasa said on Thursday would be the closest fly-by predicted to date for an object this large.
The 2012 DA 14, discovered by chance by astronomers after passing nearby last February, will be just about 27,700km above Earth’s surface when it speeds by, the US space agency said.
That is outside the Earth’s atmosphere, but closer than the orbit of most weather and communications satellites.
However, despite the close shave, Nasa said there was nothing to fear. "This asteroid’s orbit is so well known that we can say with confidence that even considering it’s orbital uncertainties, it can pass no closer than 17,100 miles (27,500km) from the Earth’s surface. So no Earth impact is possible," said Donald Yeomans of Nasa’s Jet Propulsion Laboratory.
"At the same time, it will pass 5,000 miles (8,000km) inside the ring" of satellites, Mr Yeomans told reporters, saying the asteroid’s path put it right in the "sweet spot" to avoid having any damaging impact.
The asteroid is predicted to come closest to Earth on February 15, at about 7.24pm GMT, plus or minus a minute or two, and will pass over the Indian Ocean off Sumatra.
It will be visible, with a little help from a telescope, in eastern Europe, Australia and Asia, astronomers said.
"What you would see through a small telescope would be something like a star, a small point of light ... that moved against a background of stars," said Tim Spahr, of the Harvard-Smithsonian’s Minor Planet Center.
The asteroid measures about 45m in diameter. That makes it relatively small by celestial standards.
"The object that ... took out the dinosaurs was about 10km (wide)," said Mr Yeomans.
Nevertheless, if it were to hit the Earth, the impact would be roughly equivalent to a 2.4-megaton bomb — enough to flatten a large area but not globally catastrophic, he explained.
Nasa estimates an smallish asteroid such as 2012 DA 14 flies close to the Earth every 40 years, on average, but only hits the Earth once every 1,200 years.
Statistically speaking, that means we’re probably safe for quite a while, since a similar asteroid hit just more than 100 years ago.
"With an estimated size of the order of 50m, (2012 DA 14) is comparable in dimensions to the object that destroyed more than 2,000 square kilometres of forest in Tunguska, Siberia, on June 30 1908," said Mark Bailey, director of the Armagh Observatory in Northern Ireland.
Astronomers have detected about 9,500 celestial bodies of various sizes that pass near Earth, but they estimate that is only a 10th of what’s out there.
Even 2012 DA 14 was almost missed last year, because of how quickly it passed through the observable sky, said Jaime Nomen, one of the astronomers who spotted it from the La Sagra observatory in southern Spain.
"It was an elusive target, and it could have been undetected," he said.
But Nasa, in its teleconference on Thursday, emphasised that it was keeping a careful watch on the skies, including telescopes that make nightly sweeps, with ever-improving technology.
"We’ve found about 95% of those larger asteroids that come close to the Earth," said Lindley Johnson, a top official in the space agency’s Near-Earth Object Observations Program.
Smaller objects, such as 2012 DA 14, are more numerous and harder to spot, he said, but Nasa has found "lots" of them.
And based on the agency’s observations and analysis, this is the nearest brush for an serious asteroid impact for the foreseeable future.