Detective Mission will help Researchers to Trace the History of a New African Meteorite

Detective Mission will help Researchers to Trace the History of a New African Meteorite

Benenitra received debris from an ancient meteorite, which is now named after the town.

On 27 July 2018, debris from a meteorite landed in and around the small remote town of Benenitra in southwestern Madagascar, shortly before a lunar eclipse. This prompted researchers from Wits and colleagues from the University of Antananarivo in Madagascar to investigate, describe, classify, and trace the history of the meteor.

Tim Marais, a Wits Geosciences graduate, traveled to the area soon after the meteorite fall and collected some preliminary eyewitness accounts and several fragments from residents who reported a bright meteor fireball, a loud explosion, and a rain of rock fragments that fell in and around Benenitra. Fortuitously, the debris missed the people and buildings. He delivered these fragments to his Professors (Roger Gibson and Lewis Ashwal) and asked them to verify their extra-terrestrial origin.

Small spheres in the rock matrix appeared promising indicators of a dark fusion crust and school’s Senior Technician, Caiphas Majola, was immediately commissioned to prepare a thin section of a fragment for microscopic analysis. The assessment of the fragments confirmed its meteorite status and identified it as a common chondrite. Results dated the meteor back to our Solar System formation, 4.56 billion years ago.

On 4th August, the local Triatra Gazette newspaper reported eyewitness accounts of a large specimen showing a similar black fusion crust. Seeing similarities, Dr. Andry Ramanantsoa from the Laboratory of Seismology and Infrasound at the University of Antananarivo was asked to investigate if a significant explosion occurred around the evening of 27 July in the atmosphere above Madagascar. Ramanantsoa confirmed that an upper atmosphere energy release event did take place at 5.16 p.m. GMT (7.16 p.m. local time). He used infrasound data from the International Comprehensive Nuclear Test Ban Treaty Infrasound Station IS33 outside Antananarivo.

In order to gauge if the blast wave from the atmospheric detonation had the magnitude to generate ground vibrations, the researching team turned to Dr. Andriamiranto (Ranto) Raveloson, a Postdoctoral Fellow and Technical Manager of the Africa Array Seismic Network co-ordinated from Wits. He confirmed an extremely faint seismic tremor at 5.17 p.m. GMT, the same night. Final confirmation of the 27 July event was obtained by Dr. Matthias Laubenstein, who works at the Istituto Nazionale di Fisica Nucleare in Italy. He measured the meteorite for rare cosmogenic nuclides, created when an asteroid in space is bombarded by high-energy cosmic rays. His measurements showed high levels of cosmogenic nuclides that could only form within the meteorite if it entered Earth’s atmosphere within the past few months.

Ashwal and Gibson refined the meteorite’s classification, L6 chondrite, referring to its low iron content. The digit ‘6’ refers to high levels of recrystallization occurring within the chondrules via temperature build-up. Chondrules are cosmic building blocks for rocky bodies like asteroids and the Inner Planets. As these bodies grew larger, heat built up inside them — partly through gravitational collapse and partly because of radioactive elements — causing metals and chondrules to recrystallize and perhaps melt. Sufficiently high temperatures melt the body, allowing denser metals to settle near the bodies’ core, and dense silicate melts to rise towards the surface. Eventually, the body cooled down and solidified.

Apparently, the Benenitra meteorite got quite hot but melted partially, allowing some chondrules to survive. Evidence in the form of a thin shock-melt vein within fragments suggests a collision with another asteroid shattering the meteor sending fragments hurtling towards Earth. Gibson referred to that by saying,

“Meteorites are commonly called The Poor Man’s Space Probe, because they deliver rocks from Outer Space to our door for free, where we can study the birth and history of other parts of our Solar System. The Benenitra meteorite is a new Space rock, but it is also a witnessed fall, which makes it part of a special group of meteorites. It is part of our collective heritage as a species, planet, and Solar System. It fell in a remote area that will henceforth be recognized internationally for the event on the evening of 27 July. Our project provides an opportunity to further strengthen scientific collaboration in the SADC region. Ultimately, one of our goals is to inform the people of about the significance of what they witnessed and thus build greater awareness of science.”

A range of tests is being conducted on the meteorite fragment to establish its properties, its density, and magnetism. The team plans to deliver a comprehensive scientific paper on Benenitra (the name given to this meteorite) pretty soon.

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