An asteroid half the size of a football field passed closer to Earth than any other known object of its size today.
It came just hours after an unrelated and much smaller space rock blazed over central Russia, creating shock waves that shattered windows and injured 1,200 people.
Asteroid 2012 DA14, discovered just last year, passed about 27,700 km from Earth at 8.25am NZT, closer than the networks of television and weather satellites that ring the planet.
New Zealand astronomers tracked the asteroid's path early today.
While the spectacular space rock display above the Ukraine was going viral around the world, Dr Grant Christie of Auckland's Stardome Observatory was preparing for an astronomical close-call.
"DA14 is the closest body of this size that's ever been observed to the Earth. So that was about 27,000 kilometres above the surface of the Earth," Christie told ONE News.
Twenty seven thousand kilometres is a tight squeeze in space terms - one tenth of the distance to the Moon and closer than many satellites.
Just 50 metres in diametre, DA14 is not a big asteroid. But if it had hit Earth, all 190,000 tonnes of it would have caused a lot of damage.
"That's a very near miss," Christie said.
"In 1908 something of similar size barreled into the atmosphere over Siberia and detonated above the ground and flattened thousands of square kilometres of forest."
An asteroid and a meteor are the same thing, space rocks. But unlike a meteor, which burns brightly as it enters the atmosphere, an asteroid passing through space is a less spectacular affair.
But for amateur astronomer John Whitby, observing from Carterton, it was all worthwhile.
He said the asteroid was "a little wee pinhead of white light passing through the sky amongst the stars."
It was "very exciting because it was the first time I've actually tracked an asteroid, especially exciting with one coming so close to the Earth," he said.
Christie said there are possibly one million objects of the asteroid's size that potentially could hit the Earth that aren't known.
We don't find out about them very long in advance. Most of the time you might only get days," he said.
Scientists said the two events, both rare, are not related. The body that exploded over Chelyabinsk, Russia, yesterday came from a different direction and different speed than DA14.
"It's simply a coincidence," said NASA scientist Paul Chodas during a webcast showing live images of the asteroid from a telescope in Australia.
NASA has been tasked by the US Congress to find and track all near-Earth objects that are 1 km 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 of sending up a spacecraft or taking other measures to avert catastrophe.
About 66 million years ago, an object 10 km in diameter 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.
Scientists estimate that only about 10% of smaller objects, such as DA14, have been found.
"Things that are that tiny are very hard to see. Their orbits are very close to that of the Earth," said Paul Dimotakis, a professor of aeronautics and applied physics at the California Institute of Technology in Pasadena.
Asteroid DA14, for example, was discovered last year, and it was found serendipitously by a group of amateur astronomers.
"This is a shot across the bow," Dimotakis said. "It illustrates the challenge of the observation campaign which is now in progress."
The planet is regularly pelted with objects from space, adding up to about 100 tonnes of material per day, said astronomer Donald Yeomans, with NASA's Jet Propulsion Laboratory in Pasadena, California.
Rocks the size of basketballs come in every day. Things the size of a small car arrive every couple of weeks. Larger meteors are less common, so the frequency of hits decreases, Yeomans added.
Difficult to see ahead of time
The rock that broke apart over Russia was believed to be a tiny asteroid, estimated to be about 15 metres - more than twice the size of a small car - and travelling at 18 km per second, NASA said.
"These things are very faint until they get close enough to the Earth to be seen. An asteroid such as this, which approaches the Earth from the daytime sky, is virtually impossible to see ahead of time because telescopes have to look in the night-time sky to discover asteroids," Chodas told reporters on a conference call.
The asteroid weighed about 7000 tonnes, and created a fireball trail visible for 30 seconds - in daylight - as it plummeted through the atmosphere.
Shock waves from the blast shattered thousands of windows and damaged buildings. Many of the 1200 people injured were hit by flying glass, Russia's Interior Ministry said.
"You can see what sort of destruction and shock wave that a smaller asteroid can produce.
It's like Mother Nature is showing us what a tiny one can do," Chodas said.
The Russian fireball was the largest space rock to hit Earth's atmosphere since the 1908 Tunguska event when an asteroid or comet exploded over Siberia, levelling 80 million trees over 82,150 sq km, NASA said.
Asteroid DA14 blazed past the planet at about 13 km 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 tons of dynamite, the equivalent of hundreds of Hiroshima-type bombs.
"It's a good thing it's not hitting us, because truth be told there's nothing we could do about it except possibly evacuate, which is not going to be easy given the uncertainty about where the impact would take place," Dimotakis said.
"We would essentially take the hit," he added.