Diamonds found inside a meteorite have revealed the story of a “lost planet” from the era in which our solar system was first formed.
The unusual composition of the Almahata Sitta meteorite immediately drew the attention of scientists after it plummeted to Earth in 2008, crash-landing in Sudan’s Nubian Desert.
Examination of its structure has now provided the first physical evidence for a theory about how the planets of the solar system – including Earth – came to be.
The analysis revealed the meteorite is a fragment of one of the “building blocks” of which they are thought to be constituted.
“Before you end up with the nine planets, you had a population of larger bodies a few thousands of kilometres in size – Mercury to Mars size I would say – that were populating the solar system,” Professor Philippe Gillet, a geophysicist at the Ecole Polytechnique Federale de Lausanne (EPFL), told The Independent.
“These ‘proto-planets’ were colliding into each other, forming the planets we know today.
“These were the building blocks.”
This is the theory, but what scientists have been missing before now is the evidence to support it. Remnants of those early planets have never been found.
“Because we had collisions you should find some remnants of that,” said Prof Gillet, explaining what led him and his team to the Almahata Sitta meteorite.
Upon examining the astronomical body, the researchers found signs in its mineral structure that suggested a remarkable origin story.
“We have in our hands the remnants of one of these planets that were populating the solar system just before the end of its formation,” he said.
The rock belongs to a rare class of meteorites known as ureilites, which have long been thought to have ancient origins.
Work by Prof Gillet and his colleagues has now provided the first evidence these bodies are in fact left over from proto-planets.
In making this discovery, the team led by graduate student Farhang Nabiei has substantiated the existence of these “lost” planets long predicted by planetary formation models.
The results of this analysis were published in the journal Nature Communications.
To arrive at their conclusion, the scientists used electron microscopes to zoom in on the crystal structures of tiny diamond clusters embedded in the meteorite.
“Ureilites are very rich in carbon, and many of them are very full of diamonds – and we were trying to understand the mechanisms that formed these diamonds,” said Prof Gillet.
Generally, these kinds of clusters can be formed when the material is subjected to sharp shocks of temperature and pressure – a fairly unremarkable finding for a body such as this one.
However, the scientists noticed that within the meteorite were larger chunks of diamond, which would take much longer to form.
Examination of imperfections found within the diamonds allowed the scientists to determine the exact conditions in which they came to be.
“These imperfections, they tell us a lot about the pressure and temperature history of the body,” said Prof Gillet.
The scientists found the diamonds had been created under enormous pressures above 20 gigapascals, indicating they were formed inside a large planet-like body from the first 10 million years of the solar system.
As other fragments from the solar system’s early days came together to form planets, collided with the sun or were ejected into the wider galaxy, the Almahata Sitta meteorite remained nearby for billions of years – before finally crashing down to Earth a decade ago.
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