Metric analysis

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

This image shows meteors skimming the atmosphere on a single night in March this year. Author provided

Meteorites hit New Zealand three or four times a year, but the fireball that streaked across the sky over the Cook Strait last week was unusual.

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

Witnesses described a “giant bright orange fireball” and lightning that left a “smoke trail that lingered for a few minutes”.

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

The fragmentation of the meteor produced a shock wave powerful enough to be picked up by GeoNet, an array of earthquake seismometers, with a flash bright enough to be recorded by a global lightning tracking satellite. Metservice Wellington radar detected the remaining smoke trail south of the tip of the North Island.

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

As part of Aotearoa FireballsA recently established collaboration between the Universities of Otago and Canterbury and the astronomical community to track down freshly fallen meteorites, we deploy specialist meteor cameras in the night sky across New Zealand.

Fireballs Aotearoa’s meteor cameras only operate at night, but compiled witness reports reveal that the July 7 fireball traveled northwest to southeast and most likely broke up over the ocean. Unfortunately, all meteorites are therefore probably inaccessible.

Meteorites on Earth

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

Meteorites are scientific gold mines. Some contain materials from before the formation of the sun. Others tell us the story of the young sun’s planet-forming disk, when dust circulating around it began to clump together into larger rocks and, eventually, planets.

Lunar meteorites show that the moon was born from the collision of a small planet with the 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 the resulting meteorites potentially located. The trajectory also tells us the orbit before the impact of the meteor, allowing us to estimate where it came from in the solar system.

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 hit an Ellerslie roof in 2003. Our analysis shows that this rock belongs to the ordinary group of chondrites and was therefore part of a small asteroid barely younger than the sun.

Last year the British citizen led UKFall fireball network captured footage of a massive fireball over southern England. The the debris was located on a driveway in Winchcombe, Gloucestershire, where the owner first assumed someone had emptied his barbecue.

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

This is similar to the 5g of hardware returned in 2020 from asteroid Ryugu by spacecraft Hayabusa 2except the meteorite gave scientists a hundred times more to work with.

Although the July 7 Wellington fireball probably didn’t drop a meteorite on earth, the next one might. And you can participate in the hunt for meteorites by reporting any sightings to Aotearoa Fireballs.

All-sky cameras capture a bright fireball event

Provided by The Conversation

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