A space scientist has a likely explanation for a mysterious light streaking through the night sky seen by scores of people around the country – it was a meteoroid.
Dozens of people reported a mysterious explosion akin to a “sonic boom” that coincided with strange lights streaking across the sky shortly after 9pm on Saturday.
Reports flooded in from residents throughout Canterbury and as far as Wellington, Timaru and the Wairarapa.
Crown science institute GNS had said “seismic traces moving at about the speed of sound” picked up by monitoring equipment was not likely to be an earthquake but could not confirm when and where it had come from.
But Dr Duncan Steel of Xerra Earth Observation Institute said the light, as well as the noise, was “very likely” to have been the entry of a natural meteoroid – a “lump of rock in space”.
Steel guessed the meteoroid was between the size of a basketball and a fridge – though likely closer to the former – with a mass of between 20 and 200 kilograms.
He said the meteoroid, also known as a “fireball” or “bolide” when this bright, was likely to be a chip off of an asteroid.
Meteoroids start to glow as they heat up entering the atmosphere at “extremely high speed”, about 20 kilometres per second, something often mistaken for burning, before parts break off or it shatters.
“A lot of the brightness you see is actually due to the atmosphere glowing as it’s hit by the object, as opposed to the object itself glowing.”
Typically, it would be possible to see a meteoroid light up at about 100km above Earth until it was “all over and done with at about 30km”.
Steel estimated the meteoroid could have been seen across half the country, given its altitude.
The sudden bright light often seen as meteoroids hit the atmosphere is due to energy being “dumped”, after which the celestial display is “more or less over”. Witnesses often report seeing a green light or red glow.
It was possible for pieces to reach the Earth’s surface, but Steel said that was unusual and not dangerous to people.
Anna-Marie Miller, who lives in Wellington overlooking the South Island, was among those who saw the strange lights, describing it as a “bright greenish bluish shooting star that fizzled out as it came down”.
Stef Bell, who also lives in the capital, said she and her husband saw a “distinctively large, fast green streak across the sky”.
Others believed it had been a “massive falling star” that had broken up and landed in the sea.
The noise, Steel said, was likely to be from when the meteoriod shattered.
“One sees the light essentially instantaneously, but the sound is slower,” he said.
Steel, who lives in Nelson and did not see the event himself, said meteoroids enter the atmosphere about once a day, but are not often seen due to the time or location.
Meteoroids are chunks of asteroidal matter still in space before it hits the atmosphere. Meteors are the streak of light emitted when the item enters the atmosphere, and anything that makes it to Earth’s surface is called a meteorite.
The Earth is hit by about meteoroids a day but the vast majority are tiny and erode to nothing in the upper atmosphere.
To see something by the human eye, meteoroids needed to be at least about a pea or marble size, he said.
A MetService spokesman said the service had not received any reports after Saturday’s sighting, while cameras at Tekapo’s Mt John Observatory were not operating at the time.
This is not the first time a mysterious sound has left Kiwis scratching their heads.
Earlier this month, residents across six Christchurch suburbs complained about a noise described as a “heavy bass sound”, while in May last year, a nighttime droning noise was reported in North Canterbury likened to a pulsing hum.
In mid-2014, a series of puzzling “explosions” reported across West and North Auckland left police mystified.
All remain a mystery.