Watch the skies! The meteor lights up New Zealand. Photo / Supplied
Watch the skies! The meteor lights up New Zealand. Photo / Supplied
A dash visible off the North Island's East Cape in a radar was likely nothing that could be blamed on a space rock, the MetService says.
Auckland Civil Defence tweeted an image of the MetService radar last night to show there had been no lightning and that the flash acrossthe North Island sky was likely a meteor.
The MetService this afternoon clarified that a noticeable streak on the radar, seen extending off the coast near the East Cape, was likely interference that had been picked up by the Mahia-based radar at 10.30pm, half an hour after the spectacle.
"This is unrelated to the meteor seen in New Zealand," MetService meteorologist John Law said.
"The spike is a common occurrence on the radars and is often seen during sunrise and sunset."
Stardome astronomer Dr Grant Christie earlier today said it was unlikely any remains of space rock would be found in New Zealand, as its trajectory had likely ended hundreds of kilometres away from the country.
In New Zealand, only nine found objects have ever been confirmed as having come from space.
Dr Christie said it was easy for people to believe the meteorite had come down on land.
"It might look like it has landed just across the hill from where you are, or maybe in somebody's backyard - but in fact it's hundreds of kilometres beyond that - and the reason is these things are travelling so fast, in the order of 20km per second.
"So that's 20 times faster than a bullet - and in the five seconds you are seeing it streaking across the sky, it's already covered 200km - people's brains simply don't register that dimension."
It was also false to compare a meteorite to fireworks coming down - "it's much, much brighter than that" - or to make assumptions on its closeness based on its sound.
That some observers reported a time lag of five minutes after seeing the object gave some indication of its distance.
"Assuming sound is travelling roughly at a kilometre per second, the detonation was 300km away and it took the sound that long to arrive."
Dr Christie said such events happened as regularly as once a day somewhere on Earth.
"The earth is running into these things all the time - it's just that we can only see a small part of the planet from New Zealand, and therefore our chances of seeing one are reduced."
He said the last comparable event in New Zealand was on July 7, 1999, when a meteorite detonated over southern Taranaki with an equivalent energy release of 300 tonnes of exploding TNT.
That blast was powerful enough to force one Waverley farmer hard down on his farm bike - but Dr Christie said last night's event probably only packed the power of tens of tonnes of TNT.
Dr Christie agreed it was a "bolide" that had been knocked off an asteroid millions or billions of years ago.
"These fragments are circulating in the solar system and occasionally they drift into the path of the Earth - but without having a piece of it, you can't really say which asteroid it got broken off."
About 45,000 meteorites have been recorded over Earth, of which just over 1100 have been seen falling.
This Nasa map shows the frequency of small asteroid impacts around the world over a decade.
Bolide spectacle "like a lottery" - physicist
The chances of seeing a bolide soaring across the sky is a lottery, says Professor Richard Easther of the University of Auckland.
"The chance of you winning the big prize are small, but the chances that someone, somewhere will win are pretty good".
Professor Easther, head of the university's Department of Physics, wrote on his blog that those who missed last night's fireball will wait a long time before seeing another one.
Given widespread reports that the object was moving roughly north to south, there was a chance it was a piece of space junk rather than an actual meteor; many spacecraft move in orbits taking them from pole to pole.
"Objects in low earth orbit are routinely tracked from the ground, and if this was a piece of orbiting debris coming back to earth it was easily big enough that its absence will be obvious," he said.
"On the other hand, if this was a space rock it is likely to have been orbiting the sun since the birth of the solar system itself.
"For 4.6 billion years it led a largely uneventful existence, but the last few seconds of its lifetime were spectacular."
Professor Easther expected the object was much smaller than a rock that exploded above Lake Chebarkul in Russia in 2013, which created a widely-reported spectacle in the sky.
A 2002 study in the journal Nature found that hundreds of objects roughly half a metre in diameter and packing an energy equivalent to 100 tons of TNT hit the earth every year; "last night's event would have been in this size range or a tad smaller", he said.
"Really big events with an energy similar to the largest nuclear weapons ever tested occur much less often; maybe once every ten thousand years."
The rate of such large and rare events could be calculated from the number of rocks observed making a close pass to the earth, rather than by counting them as they happened.
