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Astronomers have reconstructed the 22m-year journey of an asteroid that passed through the solar system and exploded over Botswana, spraying meteorites in the Kalahari Desert.
This is the first time that scientists have traced the spreading space rock to its source – in this case Vesta, one of the largest bodies in the asteroid belt that circles the sun between Jupiter and Mars.
The six-ton asteroid entered Earth’s atmosphere at 37,000 km / h in June 2018 and split above the central Kalahari reserve, creating a fireball almost as bright as the sun. Immediate searches of the suspected landing site found a small meteorite, called Motopi Pan.
NASA researchers had tracked the dangerous object as far as the moon using telescopes in Arizona and Hawaii. After the impact, they asked Australian astronomers to check images from the SkyMapper Telescope in New South Wales – used to study black holes and the like – in case it also captured the asteroid’s flight path. Much to the amazement of researchers, this was the case.
“We would not have noticed that it had not been the report of the American discoverers, and it is striking close to home,” said Christian Wolf, astronomer at Australian National University. “Granted, this is the Kalahari and I have never been there, but when your daily job is to orient yourself along a chain of black holes with an average pitch of 1 billion light years between points on the way, the Kalahari feels awfully close to your keyboard. “
Snapshots of the asteroid, named 2018LA, from three distant telescopes on the Earth’s surface have allowed astronomers to reconstruct the rock’s path and locate its origin. The trail led to Vesta, a 300 mile wide asteroid that is sometimes visible without a telescope.
Armed with a good idea of the asteroid’s trajectory, scientists were able to refine the location of its landing in the game reserve. This led to expeditions that recovered more than 20 other meteorites spread over a 3 mile plot.
Mineralogical analyzes of the fragments suggest that the piece of rock that became 2018LA was originally buried deep below Vesta’s surface but was thrown into space in an impact that left a crater on the asteroid. about 22 million years ago.
The ejected space rock wandered through the solar system, its surface being battered by cosmic rays, until it fell into Earth’s gravitational arms and collapsed to the ground.
Laboratory tests have shown that the oldest grains inside the meteorites discovered date back to 4.56 billion years ago, a time when the solar system was still forming from a very hot disk. of interstellar gas and dust. Details are published in Meteoritics and Planetary Science.
“It’s a really exciting study,” said Ashley King, a planetary scientist at the Museum of Natural History who was not involved in the work. “This is only the second time that a rock has been detected in space before entering Earth’s atmosphere and eventually becoming meteorites on the ground.”
He said the rocks recovered were a mixture of types of igneous meteorites known as HED, an acronym for howardites, eucrites and diogenites, which have long been considered fragments of the asteroid Vesta. The asteroid was visited by NASA’s Dawn mission a few years ago.
“Because the team followed the rock from space to the impact site, they were able to calculate a very precise orbit that corresponds to an origin near Vesta, providing one of the best links we have between an asteroid and meteorites, ”King said. “Knowing where meteorites come from gives us a context of how they formed and is really important for understanding the history of our solar system.”
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