Eastern Cape meteorite find revealed
- Wits University
The spectacular entry of a meteorite into Earth’s atmosphere has unleashed a chain of events that would not be out of place in a Hollywood movie script.
At 8:52 am, residents from areas as far afield as the Garden Route on South Africa’s South Coast (200km away), the Karoo, the Western Cape and Free State Provinces – all 300km (186 miles) away, saw a bright streak of blue-white and orange light moving through the sky before it split into several smaller streaks, which then disappeared.
Sitting on a dune at the top of Cape St. Francis bay on the South Coast, friends Zoë van der Merwe, Stephen Sharp, and MC Fereira were enjoying the rare mild and calm weather. Facing north, Stephen saw a bright flash in the sky to his left. As he yelled, Zoë pulled out her cell phone and started filming several streaks of light travelling from left to right above the large dune in front of them before the lights winked out one by one.
The friends rushed down from their perch and ran in the direction of the streaks, to see if they would see pieces falling into the sea. While they saw no obvious signs on the calm sea, they heard three loud explosions, one after the other, which died away in a low rumble.
“We could actually feel the sound vibrating through our bodies, and the ground shaking under our feet,” said MC.
Not far from where they were standing, the event was witnessed by Rocco Erasmus, a boat skipper on a whale-watching tour off Cape St Francis point. He later recalled what he had seen as bright moving lights and a loud noise like thunder.
Up north, near the town of Nqweba (formerly Kirkwood), nine-year-old Eli-zè du Toit was sitting with her family on the porch of her grandparents’ house. She heard a sound like thunder that rumbled on for several seconds and getting louder. The noise was so loud that her mother thought a plane had crashed nearby, while her grandfather speculated that a part of the cliff up the valley had collapsed.
Looking up into the partly cloudy sky, however, Eli-zè was surprised to see a large dark rock fall from the sky, near a Wild Fig tree in the garden, and hit the ground.
The rock looked black and shiny on the outside. However, it had broken up into multiple pieces and looked like concrete on the inside. When she picked up the largest piece, she said it felt “felt warm like a cup when you’ve just finished drinking the tea or coffee from it on the outside, but the inside felt cold.” By the time she carried it to the porch, the warmth was gone.
The initial media reports of the fireball speculated that it was “space junk” falling through Earth’s atmosphere. However, Dr Carla Dodd, a postdoctoral research fellow in the Department of Geoscience at the Nelson Mandela University, who was cycling with her mother in Elands River Valley northwest of Gqberha (formerly Port Elizabeth), 50km south of Nqweba, experienced the sonic boom and immediately started checking for reports of an earthquake. As the morning progressed, however, all evidence suggested that this may have been a meteorite fall.
Meanwhile, in Johannesburg, Professor Roger Gibson and his colleagues Dr Leonidas Vonopartis and Professor Lewis Ashwal, had come to the same conclusion. Having worked on other recent meteorite falls in southern Africa, the three Wits University scientists had set up a meteorite falls response action plan.
“My involvement in responding to and researching the 2 June and 27 July 2018 bolide events and meteorite recoveries in Botswana and Madagascar taught me that our response time was going to be critical if we were going to collect valuable scientific data and meteorite fragments, as well as to explain to the local public that this was a natural event and how the individual parts linked together,” says Gibson.
“Event such as these are incredible and are very exciting, both for the public who witness these falls and the scientists who gain invaluable information from studying the bolides and rocks,” says Vonopartis.
Meteorites provide scientists with the ability to “sample” the solar system, providing them with material from other planetary bodies that they are otherwise unable to acquire.
Dodd secured the sample collected by Eli-zé, and Dr Deon van Niekerk from Rhodes University was granted permit authority by the Eastern Cape Provincial Heritage Resources Authority (ECPHRA) to collect and study any meteorite samples related to the incident.
From preliminary examination of the sample, which weighs less than 100g and has a pre-fragmentation diameter of less than 5cm, the researchers suspect that the meteorite is an extremely rare type of meteorite. The specimen has a dark black glassy coating (fusion crust) with a light grey interior, peppered with dark-green and light-green grains.
This meteorite is preliminarily considered to be a brecciated achondrite from the Howardite-Eucrite-Diogenite (HED) group.
“Achondritic meteorites are less common than other meteorites and are analogous to some of Earth’s rocks. Achondrites are of great interest to geoscientists, as they give us a glimpse into the inner workings of other planetary bodies,” says Vonopartis. “They also demonstrate that processes that formed the rocks of Earth occur elsewhere in the solar system, and analysis of these meteorites help us better understand the formation of other rocky planets and asteroids.”
According to the Meteoritical Society, meteorites are named after a geographical locality near to the location of their initial recovery, which can be easily found on a map. So the meteorite has been provisionally named after the town, “Nqweba.”
Over the next weeks, a joint team involving researchers from Wits, Nelson Mandela University and Rhodes University, as well as professional and amateur astronomers affiliated with the Astronomical Society of South Africa will gather data from official observatories and eyewitnesses to piece together the details of the events. They will also search for further samples of the meteorite.
As meteorites that fall within the borders of South Africa are classified as heritage objects by the National Heritage Resources Act (No. 25 of 1999), they may not be collected, bought, or sold without a permit.
“This is a unique and exciting opportunity for our universities to work together, but it is a massive undertaking. We will be searching for rocks as small as a 10c coin over a vast area of rugged terrain and it may be that, even with dedicated search parties, we don’t recover any additional samples. That is why it is so crucial to have observant citizens during these events, as young Eli-zé has demonstrated,” says Dodd.
While millions of meteoroids enter Earth’s atmosphere on a daily basis, these are exceptionally small; the streak of light that they emit as they enter the atmosphere, and the friction that heats them up, is very faint and brief as they burn up or slow down very quickly (hence the name “shooting star”).
Events such as the one that occurred in the Gqberha region last Sunday are rare.
“The fact that the fireball, or bolide, could be seen in daylight, and that it lasted as much as 10 seconds according to reliable eyewitnesses, signals that it was considerably bigger than the sand-to-pea-sized meteoroids and that it was thus able to travel further through the atmosphere before slowing down,” says Gibson.
The size of the fireball and the time of day also meant that many people saw it although, unfortunately, the automated meteor detection camera networks run by astronomers - which would have provided a comprehensive analytical dataset of the event – are switched off between sunrise and sunset.
Bolide events are increasingly being recorded by the global meteor camera network and satellites, and by atmospheric and ground sensors that detect the sonic booms caused by the high speed.
“What may make the Nqweba event special is that Eli-zé not only saw a small piece of rock actually falling to the ground but picked it up while its fusion crust was still cooling down. As far as I know, that has not yet been reported in other falls close to people,” says Gibson.
“At that moment, Eli-zé became the youngest ever astronaut, as she was closer to a space object than anyone on Earth. Not even the astronauts who landed on the moon were able to touch a space object that came straight out of space,” says Professor Lewis Ashwal, a meteorite expert at Wits University, who previously worked at NASA.
Although more than 75,000 meteorites have been named in the international Meteoritical Bulletin that catalogues all meteorites found on Earth, the average size of all these meteorites is little more than half of the stone found by Eli-zé. Only 51 meteorites have been documented in South Africa prior to the Nqweba fall. Of these, close to half (21) come from falls where a bolide was observed. As the global ratio of meteorites collected from falls is only 2% of the total number of discoveries, this means that in South Africa we have not really detected our fair share of meteorite finds (meteorites that cannot be linked to an observed bolide). The last meteorite to be collected from an observed bolide in South Africa occurred in Lichtenburg in 1973.
“Meteorites are rare and hold deep scientific value as they give us a glimpse of the make-up and birth of our solar system, so it is extremely important for us to track, trace and find possible meteorites that may have fallen in our country,” says Gibson. “The way they interact with Earth’s atmosphere is also important as they pose a potential threat to people if they land in the wrong place.”
In the next few days and weeks, the team will focus on collecting all the scientific data about the bolide to refine its exact trajectory. This will help narrow down the search area for other fragments, which would have scattered over many tens of square kilometres and will also, ultimately, help confirm the source region in space, and even the parent body, from which the meteorite originated.
However, the initial scientific focus will be on slicing one of the fragments to obtain a thin section for microscopic mineralogical, textural, and mineral chemical analysis, which is mandatory to fully classify the meteorite and complete the submission to the Meteoritical Bulletin Database. After that and depending on the amount of material collected and the quality of the samples, a further range of geochemical and geophysical analytical methods will be applied to learn more of its source and its history.