The equivalent of 1,800 tonnes of TNT: what we now know about the meteor that lit up the daytime sky over New Zealand
Meteorites hit New Zealand three or four times a year, but the fireballs that shot through the skies over the Cook Strait last week were unusual.
It had an explosive power of 1,800 tons of TNT and was captured from space by US satellites. This triggered a sonic boom that was heard throughout the southern part of the North Island.
Witnesses described a “giant bright orange fireball” and flashes that left “a trail of smoke that hung for several minutes”.
The fireball was most likely caused by a small meteor, several meters in diameter, that crossed Earth’s atmosphere. That is one of only five impacts greater than a thousand tonnes of energy globally in the past year. Most meteors are small, creating “shooting stars” that only briefly penetrate the atmosphere.
The meteor’s fragmentation generated a shockwave strong enough to be picked up by GeoNet, a network of earthquake seismometers, with flashes bright enough to be recorded by global lightning-tracking satellites. The Metservice’s Wellington Radar caught the trail of smoke that remained on the southern tip of the North Island.
But what are the chances of finding the fragments, or meteorites, that fell to Earth?
As part of Fireballs Aotearoa, a recent collaboration between the universities of Otago and Canterbury and the astronomy community to track recently fallen meteorites, we deployed dedicated night sky meteor cameras throughout New Zealand.
Fireball The Aotearoa meteor camera operates only at night, but collected witness reports reveal that the July 7 fireball traveled from northwest to southeast and most likely fragmented over the ocean. Unfortunately, any meteorites may therefore be inaccessible.
Meteorites on Earth
Earth mainly gets meteorites from the asteroid belt, the Moon and Mars. Ranging from those that are only visible with a microscope to giant ones, such as the 10 km wide meteorite that triggered the extinction of the dinosaurs 65 million years ago.
Meteorites are a scientific gold mine. Some contain material from before the Sun formed. Others tell us about the history of the planet-forming disk of the young Sun, when the dust circulating around it began to agglomerate into larger rocks and, eventually, planets.
Read more: When the Perseverance rover landed on Mars, there was much more we already knew about the red planet from meteorites found on Earth
Lunar meteorites show the Moon came from the collision of a small planet with Earth. Martian meteorites tell us about the surface and interior of our nearest planet. We don’t even need to send a spaceship.
If a meteor is recorded by multiple night sky cameras, its trajectory can be calculated and any resulting meteorite has the potential to be found. The trajectory also tells us the meteor’s orbit before the impact, allowing us to estimate where it came from in the Solar System.
How to help find meteorites
New Zealand has nine known meteorites. Although the fireball was not visible, the most recent was the Auckland meteorite that hit the roof of Ellerslie in 2003. Our analysis shows this rock belongs to the common chondrite group and is therefore part of a small asteroid only slightly younger than the Sun.
Last year, British-led fireball network UKFall captured footage of a massive fireball in southern England. The wreckage lay in the driveway in Winchcombe, Gloucestershire – where the owners initially thought someone had emptied their barbecue.
Now on display at the Natural History Museum in London, the Winchcombe meteorite is surprisingly rare on Earth.
This is similar to the 5g of matter returned in 2020 from the asteroid Ryugu by the Hayabusa 2 spacecraft, except the meteorite gave scientists a hundred times more to work with.
Read more: What are asteroids made of? A sample returned to Earth reveals the building blocks of the Solar System
While the Wellington fireball on July 7 may not have dropped a meteorite to land, the next one might. And you can join the meteorite hunt by reporting any sightings to Fireballs Aotearoa.
We would like to thank Jim Rowe and Jeremy Taylor, our colleagues at Fireballs Aotearoa, for their assistance in compiling this article.
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