Bizarre, oddly shaped meteorites that crashed into a jungle in Costa Rica in 2019 were “mudballs” that travelled through space unscathed for nearly two million years, a new study has found.
The ultra-rare cluster of space rocks crashed onto the forest town of Aguas Zarcas in northern Costa Rica in April 2019.
Over time, about 27kg of the strange rocks were recovered to be analysed.
“The recovery of Aguas Zarcas, too, was a small step for man, but a giant leap for meteoritics,” said geologist Gerardo Soto from the University of Costa Rica, paraphrasing Neil Armstrong’s famous words.
A new study, published in the journal Meteoritics & Planetary Science, has now unravelled the source and circumstances of the fall of these cosmic rocks.
Researchers also analysed security and dashboard camera videos of the meteor and found that it entered the Earth’s atmosphere at a nearly vertical angle at a speed of 14.6kmps.
“It penetrated deep into Earth’s atmosphere, until the surviving mass shattered at 25 km above the Earth’s surface where it produced a bright flash that was detected by satellites in orbit,” said Peter Jenniskens of the SETI Institute and the Nasa Ames Research Center.
Fragments from the shattered mass remained unbroken as they landed on the relatively soft jungle and grassy surfaces, scientists say.
“Other meteorites of this type are often described as mudballs, as they contain water-rich minerals. Apparently, that does not mean they are weak,” Dr Jenniskens said.
“The steep entry trajectory and high strength resulted in deep penetration in the atmosphere and a relatively large fraction of surviving mass,” scientists wrote.
While the intense heat of collisions with the atmosphere seems to have melted most of the meteorites, the remaining fragments suggest that their parent rock endured an unscathed long journey through space. Scientists found this by measuring how long the meteorites were exposed to cosmic rays.
“The last collision experienced by this rock was 2 million years ago,” said astrochemist Kees Welten from the University of California Berkeley.
Researchers determined the parent rock was about 60cm (23 inches) in diameter when it hit the Earth’s atmosphere.
They could also find from the trajectory that it traveled through the atmosphere that it originated from the asteroid belt.
“We can tell that this object came from a larger asteroid low in the asteroid belt, likely from its outer regions,” Dr Jenniskens said.
“After getting loose, it took two million years to hit the tiny target of Earth, all the time avoiding getting cracked,” he said.
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