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Saturday, November 26, 2022

What we now know about the meteor that lit up the daytime sky above New Zealand

Meteorites hit New Zealand three or four times a year, but the fireball that shot through the sky above Cook Strait last week was unusual.

authors


  • James Scott

    Associate Professor in Geology, University of Otago


  • Michele Bannister

    Professor of Astronomy, Te Kura Matū School of Physical and Chemical Sciences, University of Canterbury

It had the explosive power of 1,800 tons of TNT and was captured from space by US satellites. It set off a sonic boom heard throughout southern parts of the North Island.

Witnesses described a “giant glowing orange fireball” and a flash that left a “trail of smoke that hovered for a few minutes”.

The fireball was likely caused by a small meteor, up to a few meters in diameter, making its way through Earth’s atmosphere. It was one of only five impacts of more than a thousand tons of energy globally last year. Most meteors are tiny, creating “shooting stars” that only briefly graze the atmosphere.

The meteor’s fragmentation produced a shock wave strong enough to be picked up by GeoNet, a network of earthquake seismographs, with a flash bright enough to be recorded by a global ray-tracing satellite. Metservice’s Wellington radar picked up the trail of smoke that remained south of the tip of the North Island.

But what is the chance of finding any of its fragments, or meteorites, that fell to Earth?

As part of Fireballs Aotearoa, a newly established collaboration between the universities of Otago and Canterbury and the astronomy community to track newly fallen meteorites, we are deploying specialized night sky meteor cameras across New Zealand.

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Fireballs Aotearoa’s meteor cameras operate only at night, but reports compiled from witnesses reveal that the July 7 fireball traveled from northwest to southeast and likely fragmented over the ocean. Unfortunately, any meteorites are therefore likely to be inaccessible.

Meteorites on Earth

Earth mainly receives meteorites from the asteroid belt, the Moon and Mars. They range from those visible only with a microscope to gigantic ones, such as the roughly 10 km wide meteorite that triggered the extinction of the dinosaurs 65 million years ago.

Meteorites are scientific gold mines. Some contain material from before the formation of the Sun. Others tell us about the history of the young Sun’s planet-forming disk, when the dust that circled around it began to clump together into larger rocks and, eventually, into planets.

Lunar meteorites show that the Moon originated 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 meteorites potentially located. The trajectory also tells us the meteor’s pre-impact orbit, allowing us to estimate where in the Solar System it originated.

How to help find a meteorite

New Zealand has nine known meteorites. Although the fireball was not seen, the most recent was the Auckland meteorite that collided with an Ellerslie roof in 2003. Our analysis shows that this rock belongs to the common group of chondrites and was therefore part of a small asteroid. just a little younger than the Sun.

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Last year, the British fireball network UKFall captured footage of a massive fireball over southern England. The wreckage was located on a sidewalk in Winchcombe, Gloucestershire – where the owner initially assumed someone had emptied his grill.

Now on display at the Natural History Museum in London, the Winchcombe meteorite turned out to be an incredibly rare type on Earth.

It’s similar to the 5g of material returned in 2020 from the asteroid Ryugu by the Hayabusa 2 spacecraft, except the meteorite gave scientists a hundred times more to work with.

While Wellington’s July 7 fireball likely didn’t knock 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 help in compiling this article.

The Conversation

James Scott receives funding from the MBIE Participatory Science Platform to build and deploy night cameras in Otago.

Michele Bannister receives funding from the Royal Society of New Zealand Te Apārangi to explore small worlds across the Solar System.

/Courtesy of The Conversation. This source organization/author(s) material may be one-off in nature, edited for clarity, style, and length. The opinions and opinions expressed are those of the author(s).

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