New method allows tracking origin of meteorites older than the Sun

Meteorites are fundamental to our understanding of the beginning of the Solar System. They are like the leftovers of a work that keeps part of the environment of this distant past of our planetary system. Some formed with the death of stars similar to the Sun and carry secrets even older than they. Now, a new approach led by scientists at Washington University offers a glimpse into the chemistry of these stars and a pre-solar period.

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One of the biggest challenges in the study of pre-solar grains is to determine their origin, that is, from which star they formed. Previous research has been able to determine, for example, the age of these elements. However, Nan Liu, a professor at Washington University and the main author of the new approach, believes that the methods used so far to determine the nature of these space fragments were not the best.

Electron microscope image of a carbide silicon extracted from the meteorite (Image: Reproduction/NASA/Nan Liu/Andrew Davis)
For the study, Liu and his team analyzed samples of Murchinson meteorites — about 100 kg of meteorites that fell in the Australian city of Murchinson in 660. The scientist explains that these meteorites are primitive, that is, they formed at the beginning of the Solar System and since then they remain practically intact. “Most meteorites that come from the asteroid belt suffer collisions and heating,” he adds.

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These meteorites in question have grains even older than the Sun in its material. “These grains are made of silicon carbide, that is, silicon and carbon atoms,” explains Liu. However, silicon carbide does not form naturally in our planetary system. For researchers, the likely origin of these fragments are carbon stars (red giants) whose atmosphere contains more carbon than oxygen.

Spectroscopy of silicon carbide grains (Image: Reproduction /Nan Liu)

Previous measurements reveal rates of carbon isotopes and much lower nitrogen in these grains, explains Liu. According to her, these space rock fragments spent hundreds of millions of years in the interstellar medium and billions of years in the Solar System. Therefore, the surface of this material may have absorbed other elements at that time. So the researchers developed a method that would remove any impurities from these grains.

First, they dissolved pieces of the meteorite in acid until they became tiny fragments of silicon carbide. These grains were then bathed in beams of cesium and oxygen ions to get rid of any traces of recent components. At the end of the process, the team performed spectroscopic measurements of their isotopic composition.

Now, the results were much closer to the data from observations of carbon stars, according to Liu. In addition to confirming the original suspicion as to the origin of these grains, the discovery offers a new opportunity to understand more about this specific type of star. But Nan Liu points out that further research is still needed to confirm this approach.

The study was published in the scientific journal Astrophysical Journal Letters.


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