Scientists have released an analysis of a meteorite fragment collected after an asteroid’s near collision with Earth in 2008. They show that the parent asteroid was massive, and the results suggest that special, water-bearing asteroids may be larger and have different mineral compositions than previously thought.
The findings of the investigation were published this week in the journal Nature Astronomy and look at the chemical composition of a piece of those meteorite fragments.
The story of the fragments begins in October 2008, when scientists became aware of an asteroid on a collision course with Earth. They knew that most of the rock would burn up upon entry into Earth’s atmosphere, and that its remains, if any, would fall into the windy sands of the Nubian desert. It presented a unique opportunity for an international team of researchers, including NASA scientists, to anticipate the arrival of the rocks and then comb the sand in search of leftover fragments.
Although the asteroid was relatively small – only about nine tons – the debris was miniscule; less than 8.8 pounds (4 kilograms) of meteorite were collected from the desert. They were collectively called Almahata Sitta, after a nearby train station. It was the first time an asteroid had been seen and after that the meteorite debris was collected.
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Since the recovery, several pieces from Almahata Sitta have been analyzed, revealing information about the origin and chemical composition of different parts of the asteroid. The meteorite sample the team studied–called AhS 202 – was so small you could place 10 copies of it on a nailhead, but it came from a giant space rock, an origin point that precedes the fragment’s merging with the rocky mass of Almahata Sitta. The team used infrared and X-ray light to study the sample. They found that the fragment was a carbonaceous chondrite, a type of meteorite that formed in the early days of the solar system that may have brought water to Earth, giving rise to … all of this. Carbonaceous chondrites were generally not thought to be from parent bodies (native asteroids) larger than about 100 kilometers in diameter.
But the researchers found tremolite in their tiny fragment, a mineral that requires a tremendous amount of pressure to form. The existence of tremolite in the sample suggests that the diameter of the original asteroid is in the range of 398 to over 1,119 miles (640 to over 1,800 kilometers), placing it in the wheelhouse of Ceres, the largest object-actually a dwarf planet– in the asteroid belt.
“This is evidence of a very large maternal body that we were unaware of existed,” said Vicky Hamilton, a staff scientist at the Southwest Research Institute and lead author of the recent paper, noting that this was the first known presence. from tremolite in a carbonaceous chondrite. “The fact that we have no other evidence for it in our meteorite collections helps confirm what we already suspected, namely that the meteorites we can find on Earth are a biased monster.”
As asteroids sweep through space, they will undoubtedly make contact with other bodies. These conglomerations of metals and minerals converge and disintegrate as their trajectory progresses. When a meteorite is actually found on Earth, it is a sequential compendium of stories from space, and the only way to read it is to run a whole series of analyzes.
“You can have a group of scientists look at one piece of a meteorite and another group at another piece of that same meteorite, and you will see two different parts of the history of the solar system,” Hamilton said.
That’s how Hamilton’s strip could speak of an origin in a massive asteroid, while another stretch of Almahata Sitta could hint at the one-off existence of a proto-planet. The electroscopy work the team did recently is kind of reverse engineering, going from what looks like a typical space rock to its specific story, in this case the reference to a massive parent asteroid. It’s like finding a crumb on your counter – it could come from anywhere – but if you look at it chemically, you can tell what temperature and pressure conditions triggered it, and if that crumb was really from this morning’s toast or came from last week’s birthday cake.
Although much rarer than other types of asteroids, new information about carbonaceous chondrites could fall out of the blue at any time. It’s just a matter of whether meteorites are watchful – or lucky – to see them.