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ASTROPHYSICS

A meteorite in Serra Pelada

Fragments of one of the largest asteroids in the solar system recovered by researchers in Amazonia

At 10:35 a.m. on June 29, 2017, a fireball crossed the sky from northeast to southwest and exploded with a boom that was heard for miles around. The meteorite broke apart and fell to the ground in the village of Serra Pelada, in the southeast of the Brazilian state of Pará. Some residents collected pieces that fell near a school; one 5.4-kilogram (kg) fragment fell on the premises of a mining company and was collected by an electrician. Geologist Marcílio Rocha, who was born in the village, had an idea about what the rock was and contacted meteorite specialist Maria Elizabeth Zucolotto, a researcher at the National Museum of the Federal University of Rio de Janeiro (UFRJ).

Studies conducted by researchers from the states of Rio de Janeiro, Pará, Bahia, and São Paulo indicated that it was a rare type of meteorite that probably broke apart from Vesta, one of the largest and brightest asteroids in the solar system. At 500 kilometers (km) across, Vespa is part of the asteroid belt located roughly between the orbits of Mars and Jupiter. “Asteroid collisions can cause pieces to break off and enter into orbit around the Sun,” says astronomer Thais Mothé Diniz, who studied meteorites at UFRJ’s Valongo Observatory and is currently a professor at the Norwegian University of Science and Technology in Alesund.  “When they pass close to Earth, they can enter our atmosphere, which is when they become known as meteors.” When they reach the surface of the planet, they are called meteorites.

The meteorite that landed in Pará, which was named after Serra Pelada, is a basaltic rock primarily composed of two minerals—feldspar and silicates—known as pyroxenes, as well as lower volumes of quartz and apatite, as described in an article published in the journal Anais da Academia Brasileira de Ciências (Annals of the Brazilian Academy of Science) in February 2018.

According to Zucolotto, who was lead author of the paper, the Serra Pelada meteorite entered Earth’s atmosphere at a speed of somewhere between 11 and 70 km per second. As it was slowed down by friction with the air, it exploded into several fragments. But only two pieces were recovered—many others, possibly smaller in size, were lost in the rainforest. Zucolotto’s study reinforces the hypothesis that the meteorite came from Vesta, based on the unique chemical composition of the asteroid.

It was the first recorded meteorite to have landed in Amazonia and is the third Vesta fragment to have been collected in Brazil. The first was the Serra de Magé, which weighed about 1.8 kg and fell in the municipality of Alagoinha, Pernambuco, in 1923. The second was the Ibitira, which weighed about 2.5 kg and fell in the municipality of Martinho Campos, Minas Gerais, in 1957. The largest meteorite ever found in Brazil is the Bendego, weighing in at 5.36 tons, which was discovered in the state of Bahia in 1784. To date, 74 meteorites have been identified in Brazil.

“Meteorites are composed of the remnants of what formed our solar system, as well as fragments of larger bodies, such as asteroids, the Moon, Mars, and possibly comets. They are important pieces in the puzzle of how the planets formed and evolved, offering samples of the bodies from which they originated, from the core to the surface. Some of them, such as chondrites, retain the same composition as they had 4.56 billion years ago, dating back to the origin of the solar system,” says Zucolotto.

When Rocha called to tell her about the event, Zucolotto was searching for fragments of another meteorite in Palmas de Monte Alto, Bahia. She changed her plans and traveled immediately to the village of Serra Pelada, 1,800 km away, where she and collector André Moutinho began looking for traces of the rock. They searched through hidden gold mines, met members of the Landless Workers’ Movement in Eldorado dos Carajás, and travelled along isolated stretches of the Trans-Amazonian Highway.

After six days of searching, they found no signs of the meteorite, and they knew that the 5.4 kg piece they came for had already been sold to a foreign buyer. They left with just a few fragments, which they bought for R$37,000. “Sometimes, the Friends of the National Museum Society provides funding to support these purchases,” she says.

Zucolotto has experience hunting meteorites. In 1997, she helped track down two Americans who had stolen a very rare type of meteorite from the National Museum in Rio de Janeiro. The Angrito, weighing 1.5 kg, fell in the municipality of Angra dos Reis in 1869, and the thieves replaced it with a worthless replica. The Angrito is one of the oldest rock types in the solar system, with only 28 confirmed specimens in the world. The switch was quickly noticed and the meteorite recovered with the help of the Federal Police at Galeão International Airport in Rio de Janeiro. “At the time, the Angrito had a high commercial value because of its rarity, but a very similar meteorite weighing 40 kg was recently found in Argentina, causing its value to plummet,” she says. When it was stolen, the meteorite could have been worth as much as US$3.5 million to collectors.

Scientific article
ZUCOLOTTO, M. E. et al. Serra Pelada: The first Amazonian meteorite fall is a eucrite (basalt) from asteroid 4-Vesta. Anais da Academia Brasileira de Ciências. Vol. 90, pp. 3–16, Feb. 2018.

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