Kathy Gibson reports – Scientists have confirmed that a big meteorite exploded close to Gqhberha last week (25 August), with witnesses reporting the flash and sound from hundreds of kilometres away.
Researchers from the University of the Witwatersrand, Nelson Mandela University, and Rhodes University today reported on probable origin and size of the meteorite as well as its trajectory and speed as it entered Earth’s atmosphere.
A meteorite is a small piece of a meteor that enters the Earth’s atmosphere. The one that entered over the Eastern Cape is a bolide, a type of fireball that explodes along its flight path and then disappears. On 25 August, areas of the Eastern Cape experienced hypervelocity bombardment when this happened.
Wits University’s Professor Roger Gibson explains that we are moving fast through space, and objects themselves are moving fast too – so they end up smashing into the planet. The average speed is 20km per second. As they enter the atmosphere, they cause friction, heat, melt and burn up at more than 1 800 degrees.
Most of these are small and are deflected by our atmosphere, but larger meteorites penetrate through the earth’s shield and burn brighter and longer. As they approach the earth’s surface they become more dense and their landing is more impactful.
Different types of meteorites offer rich fields for scientists to examine how the solar system and our earth formed.
About 75 000 meteorites have been collected and categorised – but because the fragments recovered are so small, they would all fit into two passenger buses, Prof Gibson says. Of these, chondrites makes up about 86%. They are the oldest rocks in the solar system and help us understand the makeup of rocky planets. Irons, about 6% of the meteorites we have collected, are the biggest individual samples. Achondrites, about 8% of the total, help us to understand how our own planet was formed.
Dr Carla Dodd, a microbial scientist from Nelson Mandela University, was the first scientist to handle the meteorite.
She relates how the story unfolded: “I was out cycling and when we heard the noise we first thought it might be thunder or an earth tremor.”
Once it was established that it was most likely a meteorite, within less than 12 hours samples had been collected, and a plan for studying them was in place.
Citizen scientists were key in capturing the bolide flight and sonic boom and collecting the first fragments.
By the Monday, Rhodes scientists had received the fragments and had consensus that it was a meteorite.
On Tuesday, Rhodes University’s Dr Deon van Niekerk received a permit to study the meteorite.
On Wednesday, scientists from Wits, Rhodes and NMU spent the day describing and cataloguing the fragments.
On Thursday and Friday, they collected reports from eye-witnesses and ear-witnesses, collaborating the flight path and strewn field.
Field trips also defined the flight path and area where more fragments might be found.
Prof Gibson explains that a bolide explodes in a terminal blast and often forms fragments. Much of it is burnt up, but some pieces do get through – in fact, about 10 to 15 meteorites make it to Earth every day.
“The atmosphere is a very effective shield against small fragments, but bigger rocks have more momentum.”
The fragments will typically be 3 tons to 5 tons, but they are very dense, so smaller than an average car. Indeed, a CNEOS (Centre for Near Earth Object Studies) reports indicates that the bolide – the 20th reported in South Africa in 2024 – was less than 1,5m-cubed.
The bolide punches through the upper atmosphere and then goes through denser and denser atmosphere, encountering more resistance. So it starts to vibrate and any fractures start to open up, causing the terminal blast.
A video captured by Zoe van der Merwe was analysed by Tim Cooper from the Astronomical Society of South Africa. It shows the original body slowing and then blowing apart.
More than 150 eye- and ear-witness reports show sightings were as much as 600km to 650km apart, with loud booms and vibrations focused along the coast near Gqeberha.
The main mass detonated over the Great Winter Mountains north west of Gqeberha.
CNEOS confirms that the bolide was travelling at 20,1km per second, with energy of 92 tons TNT, and exploding at an altitude of 38km.
Dr Van Niekerk points out that meteorites are the only physical part of the universe beyond the Earth that we can hold and touch, which makes it an exciting study.
Last week’s meteorite broke apart, and the five fragments recovered so far are just a few centimetres in diameter. “It is incredible that someone was there and picked them up,” Dr van Niekerk says.
Meteorites typically have a fusion crust, or molten outer crust, he explains.
Initial examinations suggest that the meteorite is an achondrite, and contains no metal. There are some green crystals, which indicates the presence of magnesium and other minerals.
It’s possible these are fragments of a primitive Howardite Eucrite Diogenite (HED) achondrite that possibly formed less than 5-million years after the formation of the solar system.
Some years ago, HEDs were spectroscopically linked to the asteroid 4Vesta, the second-largest asteroid in the asteroid belt, at about 530km in diameter.
A NASA mission, Dawn, visited 4Vesta between 2011 and 2018, which confirmed that long-held hypothesis that HEDs are geochemically related to the asteroid and were possibly ejected from Vesta during a long-ago impact with another space body.
The meteorite has provisionally be named Nqweba, which is the new place name for Kirkwood in the Eastern Cape. Dr Van Niekerk points out that this is a provisional name, as the fragments still have to be classified and the presented to the Meteoritical Society’s Nomenclature Committee.
Wits University’s Dr Leo Vonopartis, takes the story further and explains what will happen next.
Having done the macroscopic examination, the next step will be to measure all the physical properties. Thereafter, a thin section will be made of the material to do an optical microscopic study.
Once the mineralogy is better understood, scientists will do a compositional analysis using the automated scanning electron microscope, the electron probe microscope, and will also perform isotopic analysis.