Scientists announced on Tuesday that they have found the crater from which the oldest known Martian meteorite was originally shot at Earth, a discovery that could provide clues as to how our own planet formed.
Nicknamed the Black Beauty, meteorite NWA 7034 has fascinated geologists since its discovery in the Sahara Desert in 2011.
It’s easy to hold, weighs just over 300 grams (10.6 ounces) and contains a mix of materials including zircons that are nearly 4.5 billion years old.
“That makes it one of the oldest rocks studied in the history of geology,” Sylvain Bouley, a planetary scientist at France’s University of Paris-Saclay, told AFP.
Its journey dates back to the very beginning of the solar system, “about 80 million years after planet formation began,” said Bouley, who co-authored a new study of the meteorite.
Tectonic plates long ago covered the Earth’s ancient crust, meaning “we’ve lost that primitive history of our planet,” Bouley said.
But Black Beauty could offer “an open book about a planet’s first moments,” he added.
To open this book, a team of researchers from Australia’s Curtin University went in search of the meteorite’s original home on Mars.
They knew it was probably an asteroid hitting the red planet that sent Black Beauty rocketing into space.
The impact “had enough force to eject the rocks at very high speeds — more than five kilometers (three miles) per second — to escape Mars’ gravity,” said Anthony Lagain of Curtin, the study’s lead author in Nature Communications AFP.
Such a crater would have to be massive – at least three kilometers in diameter.
The problem? The pockmarked surface of Mars has about 80,000 craters at least as large.
– Follow the clues –
But the researchers had a clue: By measuring Black Beauty’s exposure to cosmic rays, they knew it was driven from its first home about five million years ago.
“So we were looking for a crater that was very young and big,” Lagain said.
Another clue was that its composition showed that it had suddenly heated up about 1.5 million years ago – likely from the impact of a second asteroid.
The team then created an algorithm and used a supercomputer to search through images of 90 million craters taken by a NASA satellite.
That narrowed it down to 19 craters, allowing researchers to rule out the remaining suspects.
They found that Black Beauty was excavated from its first home by an asteroid that impacted about 1.5 billion years ago, forming the 40-kilometer-long Khujirt Crater.
Then, a few million years ago, another asteroid struck not far away, creating the 10-kilometre-long Karratha crater and sending the Black Beauty tumbling toward Earth.
Like Black Beauty, the southern hemisphere region of Mars is rich in the elements potassium and thorium.
Another factor was that Black Beauty is the only strongly magnetized Martian meteorite.
“The region where Karratha was found is the most magnetized on Mars,” Lagain said.
Known as the province of Terra Cimmeria – Sirenum, it is “a relic of early crustal processes on Mars and thus a region of great interest for future missions,” says the study.
Bouley pointed to a “bias” in currently planned missions to Mars in favor of searching for signs of water and life.
But understanding how the first planets formed would answer some fundamental questions, Lagain said, including “how Earth became such an extraordinary planet in the universe.”
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