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Wits researchers and colleagues at the Antananarivo University in Madagascar are tasked with describing, classifying and tracing the story of a meteorite that has landed in and around the small town of Benenitra, in southwestern Madagascar, shortly before the lunar eclipse of July 27, 2018.
The news of the event in this remote area was brought to the attention of a Wits Geosciences graduate, Tim Marais, who was traveling to the area a few days after the meteorite fell. He gathered preliminary eyewitness accounts of a meteor fireball, a loud explosion and a rain of rock fragments falling in and around Benenitra who, fortuitously, seem to have missed all the people and all the buildings, and he could acquire several small fragments. that the residents had managed to locate. He gave them to the teachers Roger Gibson and Lewis Ashwal at the School of Geosciences in Wits and asked them to check their extraterrestrial origin. Signs of a dark melting crust and small spheres in the rock matrix visible on broken surfaces looked promising and the school's senior technician, Caiphas Majola, was immediately instructed to prepare a thin section of the rock. 39, one of the fragments for a microscopic analysis.
Retrace the story
The evaluation of the thin section confirmed that it was a meteorite and, more specifically, a relatively common type called chondrite, which refers to the small spherical chondrules it contains. This established that the meteorite dates from the formation of our solar system about 4.56 billion years ago.
At the same time, on August 4, the local newspaper Triatra Gazette published a report reporting this information and showing a large specimen with a similar black fusion crust. To scientifically corroborate the event, the team contacted Dr. Andry Ramanantsoa of the Laboratory of Seismology and Infrasound of the Institute and the Geophysical Observatory of the University of Beijing. Antananarivo to determine if there was evidence of a major explosion in the atmosphere over Madagascar at any given time. the evening of July 27th. Ramanantsoa was able to confirm, with the help of infrasound data from the IS33 (Comprehensive Nuclear Test Ban Treaty) infrasound treatment plant, outside Antananarivo, that it there had indeed been an "energy release event in the upper atmosphere" at 17:16. GMT (19h16 local). In addition, he was able to identify that it occurred in a south-southwest direction of Antananarivo – the exact bearing of Benenitra.
The next step was to determine whether the shock wave emitted by the atmospheric detonation was large enough to cause ground vibration that can be detected by geophysical seismometers. To do this, the team turned to Dr. Andriamiranto (Ranto) Raveloson, postdoctoral fellow and technical leader of the Africa Array seismic network, coordinated by Wits. He was able to confirm a very slight earthquake at 17:17. GMT the same evening. Dr. Matthias Laubenstein of the Gran Sasso National Laboratory of the Istituto Nazionale di Fisica Nucleare, Italy, confirmed that the fragment was linked to a fall on 27 July. He had measured the meteorite of rare cosmogenic nuclides created when the asteroid in space is bombarded by high energy cosmic rays. Its measurements revealed high levels of cosmogenic nuclides, which is consistent with the fact that the meteorite only entered the protective atmosphere of the Earth in recent months.
Based on these findings, the team has submitted a request to the International Meteorological Society for it to formally name and register Africa's newest meteorite, Benenitra, in its database.
Classify the newest meteorite in Africa
Ashwal and Gibson refined the classification of meteorites as L6 chondrite. The name refers to the fact that it contains a small amount of iron (the "L") and that it contains recognizable chondrules. Chondrules are the original building blocks of rocky bodies – such as asteroids and inner planets – in the space. As these bodies grew, the heat accumulated within them – partly by gravitational collapse and partly by radioactive elements – which led to recrystallization and possibly to be even the melting of metals and chondrules. When the temperatures were high enough to melt the body, the denser metals could then settle to the core of the body, the less dense silicate melts rising to the surface. Eventually, the body would have cooled enough to solidify. The Benenitra meteorite seems to have warmed enough (the number "6" refers to the large amount of recrystallization that has occurred in the chondrules due to this heating process) but has only partially melted, allowing some of the chondrules to survive.
Space probe of the poor man
The meteorite also has a fine shock-fusion vein that is probably related to a collision with another asteroid that broke the original body and sent the fragment on its collision course with the Earth.
"Meteorites are commonly called the poor man's space probe because they deliver free rocks from outer space to our door, where we can study the birth and history of other parts of our solar system, "says Gibson. The meteorite fragment Benenitra is subjected to a series of other tests to establish properties such as its density and its magnetism, and the team plans to write the results in a scientific article.
"The Benenitra meteorite is a new stone of space, but it's also a sample fall, making it part of a special group of meteorites .It is part of our collective heritage in as a species, planet and solar system, it has fallen into a remote region that will now be internationally recognized for the event of the evening of July 27, which will allow us to strengthen scientific collaboration in the SADC region and, ultimately, to inform the people of Benenitra of the importance of witnessing it and thus raise awareness about science, "says Gibson.
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