Scientists break down South Africa’s Nqweba Meteorite

Geologist Carla Dodd was cycling with her mother in the Elands River Valley near Nqweba in the Eastern Cape when they heard a sonic boom. 

Like everyone else who heard the thunderous noise on the morning of 25 August, their first reaction was: “What was that?” 

“We thought this could probably be some thunder,” said Dodd, a postdoctoral research fellow in the department of geosciences at Nelson Mandela University. “Looking up, no the clouds did not look very promising and my mom thought that maybe it’s an earth tremor.”

Back at home, Dodd checked her social media feeds and came across Jessica Botha’s post on the Snow Report SA website about meteorite fragments that had landed in her garden in Kirkwood, formerly Nqweba. A friend also forwarded her child, Zoë van der Merwe’s video of the flight of the bolide — a large exceptionally bright meteor that often explodes.

Botha’s nine-year-old daughter, Eli-zé du Toit, was sitting on her grandparents’ porch when she saw a dark rock fall from the sky and land near a wild fig tree in the garden. The rock, black and shiny on the outside with a light grey, concrete-like interior, was still warm when she picked it up. 

“When she took it to her mom, her mom thought maybe this is related to Zoe’s video, which she also saw on social media,” Dodd said. “So, she posted photos of the rocks to Snow Report SA and the rest is history.”

At 8:51am that Sunday, residents from places as far afield as the Garden Route, the Karoo, Western Cape and Free State observed a bright blue-white and orange streak of light in the sky. The meteorite, after splitting into several smaller fragments, disappeared from view. Shortly afterwards, witnesses reported hearing loud explosions and sensing vibrations.

Dodd was one of a group of scientists from the University of the Witwatersrand, Nelson Mandela University and Rhodes University who, after mounting a collaborative scientific investigation into the meteorite fall, this week unveiled the rare meteorite fragment, provisionally named the Nqweba Meteorite after the nearby town of its discovery.

Earth moves through space at a speed of 1  600 kilometres an hour. As it does, it sometimes collides with other objects in space such as meteorites, much “like a car collides with bugs on the highway”, explained Roger Gibson of the School of Geosciences at Wits University. The meteorites enter Earth’s atmosphere with a light streak, called a bolide. If large enough, the meteorites may hit Earth’s surface or will burn up in the friction from entering the atmosphere. 

“Somewhere just before 8.51am this object, which had been in space for tens of millions, hundreds of millions of years, coming from the dawn of our solar system, encountered Earth’s atmosphere and as it did so, it came in over the coastline,” said Gibson, who keeps a close watch on meteorite finds and falls in the country. 

“When you start to put it all together, the external variants are all sightings of the bolide and the bright light, but as we get closer to Gqeberha and west towards George, we find that there’s sightings, there’s also loud sound noises, sonic booms up in the air and moderately violent vibrations, you could feel the ground tremor. 

“From that, we conclude that the focus of the event was in this region between Gqeberha and George and that the body, from the eyewitness accounts, was moving towards the east-north east or north-east essentially from the coastline, moving inland.”

Bolides are one part of the spectrum of material that blitz into the atmosphere and can weigh 100 to 200 tonnes. Most are sand and pea-sized material that gets burnt up in the upper atmosphere or drifts slowly down through it 

The fragments that fall into the bolide category are typically metre-sized and heavier than a car.

“Think of [rugby player] Eben Etzebeth running into you; you’re not going to stop him. They are the lock forward of the meteor world and it’s estimated that between 10 and 50 meteorites land on the Earth’s surface every day,” Gibson said.

Two thirds of Earth’s surface is water, “so there are a lot of them sitting at the bottom of the ocean so we get excited about the few that might end up on land”.

Within two days after the event, the Centre for Near Earth Object Studies had worked out that the object was travelling at the cosmic velocity of 20km a second — or 72  000km an hour — while the energy released was equivalent to 92 tonnes of the explosive, TNT. The meteorite exploded about 38km above the Earth’s surface where it “met its match”. 

The Boshof Infrasound Array near Kimberley, which was set up to monitor missiles during the Cold War, recorded the sound of the explosion.

The object was probably the size of a motorcycle, “but we hope it was bigger. Geologists always hope stones are bigger,” Gibson quipped. 

The scientific team had so far received more than 150 eyewitnesses and “earwitness” reports. He urged the public to “keep them coming”.

Dodd, recognising the rarity and importance of Eli-ze’s find, secured the sample, while geologist Deon van Niekerk, of Rhodes University, was given permission by the Eastern Cape Provincial Heritage Resources Authority to recover all fragments from this meteor for scientific analysis.

The Nqweba Meteorite is believed to be an achondritic meteorite — a rare type in the Howardite-Eucrite-Diogenite group. It weighs less than 90g and has a pre-fragmentation diameter of about 5cm. 

The specimens have a dark black glassy coating — fusion crust — with a light grey interior peppered with dark-green and light-green grains and clasts. 

There are five fragments in total, said Van Niekerk. “It is incredible that somebody actually was at the location where these rocks fell. There might be more rocks out there that we’re going to look for but it really is a needle in a haystack.”

Leonidas Vonopartis, of Wits University’s School of Geosciences, agreed. “Having a sample, especially something with a story as it fell, and was picked up, is incredibly rare and very exciting for the South African people, international community, international scientists and South African heritage.”

The initial scientific focus will involve microscopic and geochemical analysis of the meteorite fragment to fully classify it and understand its origin. This investigation could provide insights into the meteorite’s source region in space and possibly identify its parent body. 

The hunt for more fragments will deepen. “We are working on getting permission from landowners where we are thinking that there may be some fragments,” said Dodd.

Only 51 meteorites have been documented in South Africa, and 22 meteorite falls have been recorded. As with fossils, meteorites are items of national heritage and are regulated by the South African Heritage Resources Act.

For the public, the Nqweba Meteorite is a meteorite, but for scientists, these remnants of space rock are “many different things”, Gibson said. 

“Each of these different types of meteorites plays a role in our understanding of the origins of our solar system, the formation of our Earth and possibly even our own origins as carbon-based life forms.”

Niekerk said: “You know it takes a special person to study rocks. Geologists are frequently at the brunt of jokes, but if you consider that meteorites are the only physical pieces of the world beyond our atmosphere of the universe that we can actually hold and touch, it’s really cool being able to study these rocks. They might look boring but it’s very exciting.”