Mysterious asteroid fragment is a time capsule of the early solar system

Objects from space are being thrown onto Earth all the time – asteroids, meteorites, scrap metal from dead satellites – but there is something about a space rock that could tell us more about it. dawn of the solar system.

In 2008, a meteorite later named Almahata Sitta (AhS) crashed in Sudan. Now scientists have taken another look at this meteorite and believe he was part of a monster 9-ton meteor that exploded into 600 pieces in the atmosphere, and this meteor was probably thrown here by an even bigger asteroid. It’s almost as if he’s projecting a piece of the nascent solar system directly onto our planet. Its mineral makeup reveals things about minerals that have never been found before in carbonaceous chondrites. This means that it could help us find out how water got to Earth.

“I think discoveries like ours are unexpected results,” Vicky Hamilton, who led a study recently published in Nature astronomy, said SYFY WIRE. “Meteorites containing aquifer minerals are indirect evidence of the delivery of water to early Earth, as we don’t know exactly what types of asteroid materials impacted the planet. Asteroid parent body (which no longer exists) means that ‘It is possible that even more water would be available for delivery to Earth, especially if there were other asteroids like this one. “

This piece of Alhama Sitta is identified by the Hamilton team as Alhama Sitta 202, as it is only one of the many types of meteorites crammed into Alhama Sitta.

Metamorphic rocks like asteroids and meteorites are transformed by different natural forces, and those that begin to transform at low temperatures are usually made up of many water minerals or aquifers. Water metamorphism is rare in meteorites that have reached Earth. In rocks that begin to change at higher temperatures, hydrated minerals either become more reactive or break down. The AhS fragment studied under an infrared microscope showed properties of water metamorphism. AhS is a carbonaceous chondrite, a stony meteor containing carbonaceous compounds and dotted with chondres, or pieces of spherical minerals. Some of these carbon compounds are organic materials that may or may not have been the space ingredients of life on Earth.

Carbonaceous chondrites are also believed to be one of the sources of water that occurred here when things shattered in the chaos that was the start of the solar system 4.6 billion years ago. The same goes for comets, essentially huge scoops of ice shooting through a vacuum.

“Minerals differ in their chemistry and / or their arrangement of constituent atoms,” Hamilton said. “As such, they have unique spectral signatures in the infrared, and this is what allowed us to identify the presence of amphibole in the meteorite.”

Asteroids, and their disembodied pieces that end up being meteors and meteorites, are considered debris from the birth of the solar system. Most of them float in the asteroid belt between Mars and Jupiter. Because Mars is a barren wasteland that is not covered with grass, forests, or cities like Earth, you can see the blows it received from these rogue rocks. Craters are simply harder to find on Earth, as many of them have been buried for billions of years. There is still no shortage of meteorites, but there is something that sets AhS apart from anyone you see in museums or on eBay (it really is is one thing).

Integrated in AhS are amphiboles, which are rare in carbonaceous chondrites. They are water minerals whose presence probably means that all they came loose from was a rock that contained water and underwent a long and excruciating metamorphosis. There has only ever been one other meteorite in which traces of amphiboles have been identified, and it was Allende, whose chemical composition indicates that it came from an object other than AhS. The mysterious rock that threw AhS to Earth could have been 400 to 1,100 miles in diameter. It’s about the size of the dwarf planet Ceres, and Ceres alone is equivalent to almost the entire mass of the asteroid belt.

“When we find things like AhS 202 that tell us that there were once other bodies of the same size that are now gone, it’s unexpected,” Hamilton said. “It is also unexpected because the carbonaceous chondrite meteorites that we have studied for decades have all been assumed to have originated from bodies approximately 62 miles in diameter, which tells us that our collections are not complete.”

Because AhS is more evidence of a different formation process than most known meteorites, it suggests that this process may have been more common in the early solar system than we think, although we are still not in. ignorance of its real frequency. was. Samples from Ryugu and Bennu might offer more information on this. Spectroscopy performed by JAXA’s Hayabusa-2 and NASA’s OSIRIS-REx spacecraft already suggests that the two meteorites could be carbonaceous chondrites that have undergone water metamorphism. Hamilton believes the recently explored Bennu and Ryugu are types of carbonaceous chondrites as well.

“While we don’t think Bennu or Ryugu are made of the same material as Almahata Sitta 202, all three have compositions compatible with carbonaceous chondrite meteorites,” she said. There is evidence from OSIRIS-REx and Hayabysa2 that Bennu and Ryugu’s compositions are different from known meteorites, so in this regard, all three can tell us more about the early solar system than current meteorite collections. “

This may be the only time we would want the asteroid AhS to come and throw another meteorite at us.

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Arline J. Mercier

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