A small meteorite could change our understanding of asteroids

Scientists have published an analysis of a meteorite fragment collected after an asteroid collision with Earth in 2008. They show that the parent asteroid was huge, and the results suggest that specific, water-holding asteroids may be larger and have different mineral compositions than previously thought.

The results of the study were published this week in Nature Astronomy magazine and look at the chemical composition of a sliver of these 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 when it entered Earth’s atmosphere and that the remains, if any, would fall into the windswept sands of the Nubian Desert. This provided a unique opportunity for an international team of researchers, including NASA scientists, to anticipate the arrival of the rocks and search the sand for any surviving fragments.

Though the asteroid was relatively small – only about nine tons – its waste was tiny; less than 4 kg of meteorites were collected from the desert. They were collectively called Almahata Sitta after a nearby train station. It was the first time an asteroid was discovered and then its meteorite debris was collected.

Since its extraction, various pieces of Almahata Sitta have been analyzed to obtain information on the origin and chemical composition of various parts of the asteroid. The meteorite sample that the team examined– –Called AhS 202 – was so small that you could put 10 copies of it on a nail head, but it came from a gigantic space rock, a point of origin that precedes the fragment’s connection with the rocky mass of Almahata Sitta. The team examined the sample using infrared and X-ray light. 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, creating … all of this. So far it has not been assumed that carbonaceous chondrites can originate from parent bodies (original asteroids) with a diameter of more than 100 kilometers.

But the researchers found tremolite in its small fragment, a mineral that requires immense pressure to form. The existence of tremolite in the sample suggests that the diameter of the parent asteroid is in the range of 398 to more than 1,119 miles (640 to more than 1,800 kilometers), in the wheelhouse of Ceres, the largest object –a dwarf planet indeed– in the asteroid belt.

“This is evidence of very great parenting that we did not previously know existed,” said Vicky Hamilton, a scientist at the Southwest Research Institute and lead author of the recent paper, while noting that this is the first known presence of Tremolite in a carbonaceous chondrite. “The fact that we have no other evidence of this in our meteorite collections helps confirm what we have already suspected, namely that the meteorites we find on Earth are a biased sample.”

When asteroids race through space, they have to make contact with other bodies. These conglomerates of metals and minerals come together and break apart on their way. If a meteorite is actually found on Earth, it is a composite compendium of stories from space. The only way to read it is to do a whole bunch of analyzes.

“You can have a group of scientists looking at a piece of meteorite and another group looking at another piece of the same meteorite and you will see two different parts of the history of the solar system,” said Hamilton.

In this way, Hamilton’s shard could point to some origins of a massive asteroid, while another piece of Almahata Sitta could point to that unique existence of a protoplanet. The electroscopy work the team recently did is a kind of reverse engineering to get from a typical space rock to its specific story, in this case as an indication of a massive parent asteroid. It’s like finding a crumb on the kitchen counter – it could come from anywhere – but if you look at it chemically, you can tell under what temperature and pressure conditions it was formed and whether this crumb was really from today’s morning’s toast or from last week’s birthday cake.

Although much rarer than other types of asteroids, new information about carbonaceous chondrites could fall from the sky at any time. It’s all about whether meteorites are alert or lucky enough to spot them.