Science

Ancient meteorites preserve the building blocks of the early solar system

Scientists are shedding light on the mysterious origins of ancient meteorite grains using a new method of analysis.

These grains, which are older than the solar system itself, formed into ancient stars that died before the birth of our sun. Similar stars still exist in the universe, and analysis of these pre-solar grains provides an interesting insight into the chemistry of the stars.

Scientists have tried analyzing presolar grains in meteorites before, but Nan Liu, an assistant research professor of physics at the University of Washington in Missouri and lead author of a new study, believes that previous methods for studying these grains have been too inaccurate. .

Liu and his team analyzed samples from the Murchinson meteorites, which dropped 220 pounds. (100 kilograms) of cosmic rock in the Australian town of Murchinson in 1969. Scientists who previously studied these meteorites quickly realized that this meteor shower was a fluke, and not just because one of the larger pieces broke the roof of a local barn. somehow without hurting anyone.

Related: Blue Meteorite Crystals Reveal The Wild Youth Of The Sun

“Murchinson is a primitive meteorite, which formed at the beginning of the solar system and never melted after its formation,” Liu told Space.com. “Most of the meteorites that come from the asteroid belt experience collisions and heating, which melts them, causing any pristine material from the early stages of the solar system to disappear.”

In the Murchinson meteorite, grains of rock older than the solar system are embedded in younger material. Scientists know from previous research that these grains predate the birth of the solar system because their chemical composition is different.

“These grains are made of silicon carbide, that is, carbon and silicon atoms,” Liu said. “But silicon carbide doesn’t form naturally in our solar system because we have a lot of oxygen around us and all these carbon atoms would first bond with oxygen to form carbon oxide molecules.”

The most likely origin of these grains are carbon stars, bright red giant stars whose atmospheres contain more carbon than oxygen, Liu said. To confirm this theory, scientists must find out whether the compositions of certain isotopes in meteor grains match those of carbon stars. Isotopes are varieties of the same chemical element that are differentiated by the number of neutrons in their nucleus. While some isotope compositions are common in the solar system, others can only arise within specific types of stars.

Spectroscopic images of silicon carbide grains from an ancient meteorite. (Image credit: Nan Liu)

“The isotopic ratios of these grains are very different from what we see in the solar system,” Liu said. “For example, in objects in the solar system, we can see carbon 12 to carbon 13 rations of about 89. But these presolar grains have carbon 12 to carbon 13 ratios ranging from 2 to 200, which results from fusion reactions. in his father stars. “

The same applies to the isotopes of nitrogen, aluminum and magnesium.

Astronomers were especially interested in whether the isotopic compositions found in these grains matched what observations on carbon stars revealed. But before Liu’s study, the coincidence was unconvincing. One reason could be that these stars were not, in fact, the birthplace of these grains, Liu said. However, he wonders if the explanation could be much simpler.

“Past measurements showed much lower carbon and nitrogen isotope ratios in those grains,” Liu said. “But I thought the problem could be in the analytical method. These grains spent hundreds of millions of years in the interstellar medium and billions of years in our solar system, and as a result, their surfaces may have absorbed these materials.”

That would mean that in previous studies, scientists may have measured the younger impurities on the surface rather than the pre-solar grains themselves.

Therefore, Liu and his team came up with a new analytical method designed to remove any material that could adhere to the surface of these grains. As part of this technique, they first dissolved pieces of the Murchinson meteorite in acid until they were left with only the grains of silicon carbide. They then doused the grains with beams of cesium and oxygen ions to get rid of any material that might have come from younger components of the meteorite.

After all this, the team made spectroscopic measurements of the isotopic compositions of the grains. The results were much more in line with data from observations of carbon stars, Liu said. This confirmed Liu’s original suspicion and showed that these grains likely not only came from carbon stars, but can now be used to help scientists advance their understanding of these types of stars.

“The new isotopic data obtained in this study is exciting for stellar physicists and nuclear astrophysicists like myself,” Maurizio Busso, a co-author from the University of Perugia, in Italy, said in a statement. “In fact, the ‘strange’ nitrogen isotopic ratios of presolar silicon carbide grains have been a notable source of concern over the past two decades. The new data explains the difference between what was originally present in the dust grains. of presolar stars and what was later attached, thus solving an old puzzle in the community. “

These new data, for example, provide clues to how carbon stars produce aluminum in their cores, according to Liu. However, this knowledge would have to be verified through further research, he added.

The study was published in the Astrophysical Journal Letters on Tuesday (October 12).

Follow Tereza Pultarova on Twitter @TerezaPultarova. Follow us on Twitter @Spacedotcom and on Facebook.

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