2023-06-03 03:30:13
“It was an asteroid, 1 meter in diameter and weighing around 1 tonne, spotted over 200,000 kilometers from Earth. And 72 hours later, we had a piece of it in our hand,” said Brigitte Zanda, still very emotional, three and a half months after the discovery. And yet, the adventure of this teacher-researcher at the National Museum of Natural History in Paris had only just begun.
For the first time in France, and only the third time in the history of science, an interplanetary object observed by astronomers was identified as heading for Earth (the asteroid), then seen, photographed and filmed as it entered the atmosphere (the meteor), and finally found in fragment form (the meteorites). An exceptional sequence of events… but also a public one. As the Vigie-Ciel (Skywatch) network called on scientists and volunteers to find as many eyewitness accounts of this event as possible in Normandy, meteorite hunters flocked in from France, Germany and Poland. A race against time was on.
The first 93-gram meteorite found by a student in a field in Saint-Pierre-le-Viger on February 15, two days after the luminous flash observed over the English Channel, signed the success of the Fripon Vigie-Ciel participatory science program. Created in 2017 to bring together researchers (Natural History Museum, Paris Observatory, Paris-Sud and Grenoble universities, etc.) and amateurs, the scheme includes around a hundred cameras spread across the country to determine the fall zone of any meteorites and attempt to find them.
Unlike archaeological artifacts, which can wait underground, meteorites can rapidly degrade. “They’re the only natural objects that contain metal. So they rust. You have to get them out of the ground quickly to analyze their properties,” said Zanda, an astrophysicist and cosmochemist.
The most mercantile of meteorite hunters, by picking up such a pebble from the ground, helps to preserve it. “They’re not our enemies, we need them too, but we lack a regulatory framework, and there’s no law to say who owns a meteorite found on French soil,” Zanda said.
‘Catastrophic fragmentation’
Americans Steve Arnold and Roberto Vargas, renowned for auctioning off the smallest gram of meteorite that has fallen from the sky, responded quickly. With more than 20 years of experience behind them, they were undoubtedly better than most at directing their search. The ellipse drawn on the ground by the scattering of fragments generally extends over many kilometers.
On reaching the upper layers of the atmosphere, the bolide is heated and ionized, forming a plasma at a temperature of several tens of thousands of Kelvin (K), incomparable to the 5,700 K at the Sun’s surface, which erodes most of it. It then breaks repeatedly against the wall created by the atmosphere, a process known as “catastrophic fragmentation.” The smaller, more numerous fragments are slowed down more and end up at the rear of the ellipse, with the larger, rarer ones, at the front.
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