Scientists Find 7-Billion-Year-Old Stardust in Murchison Meteorite | Planetary Science

James Marshall
January 14, 2020

Stars are formed when dust, gas and heat combine in just the right way.

When large, orphan space rocks form - such as the asteroid that produced Murchison - they, too, can pick up ancient, interstellar dust.

They discovered that the grains are the oldest solid material ever found on Earth.

"We've used this really old sample, the oldest solid samples available to science, to try to learn something about the history of our galaxy", said Philipp Heck, a meteorite expert at the Field Museum of Natural History in Chicago.

Heck and an global team of cosmochemists published the new study on Monday in the Proceedings of the National Academy of Sciences journal.

As these boomer stars reached the end of their 2-billion-year lifetimes, the stardust they sloughed off could be responsible for the spike that Heck detected.

Presolar grains are more abundant in what we would call these primitive meteorites, Professor Bland said.

In the future, Heck and others will isolate more presolar grains from meteorites such as Murchison and continue to date them using the cosmic ray technique.

The researchers detected the tiny grains inside the meteorite by crushing fragments of the rock and then segregating the component parts in a paste they described as smelling like rotten peanut butter.

"What I would do now is pick another sample and go through the same process and say 'Okay, do we find that same distribution of stuff or is there something weird about this one?'".

Once the presolar grains were isolated, the team figured out from what types of stars they came and how old they were.

They also measured the exposure of the grains to cosmic rays, highly energised particles zipping through our galaxy.

"Some of these cosmic rays interact with the matter and form new elements". So the longer a sample is exposed, the more secondary elements are formed. Heck compares it to "putting out a bucket in a rainstorm, then measuring how much water accumulated, and then we can tell how long it was outside". That means the scientists can measure the amount of these new elements in the grains to determine how long they were floating around in space - and, ultimately, how old they are.

The oldest of 40 tiny dust grains trapped inside the meteorite fragments retrieved around the town of Murchison in Victoria state dated from about 7 billion years ago, about 2.5 billion years before the sun, Earth and rest of our solar system formed, the researchers said.

In 1969, a 4.6-billion-year-old meteorite struck Murchison, Australia.

Most of the grains in the Murchison meteorite came from various stars that formed around the same time.

This stardust is between between 5 billion and 7 billion years old - older than the sun and our solar system.

"We have more young grains that we expected", Dr.

But the oldest of the grains were dated to more than 5.5 billion years, making them the oldest known material on Earth. During the solar system's birth, this dust was incorporated into everything that formed including the planets and the sun but survived intact until now only in asteroids and comets. This in turn acts as a food, helping to create new stars.

While some astronomical models assume stars form at a constant rate, Dr Heck and his colleagues' work shows that isn't the case.

"Our hypothesis is that the majority of those grains, which are 4.6 to 4.9 billion years old, formed in an episode of enhanced star formation. This is one of the key findings of our study".

Heck notes that this isn't the only unexpected thing his team found. As nearly a side note to the main research questions, in examining the way that the minerals in the grains interacted with cosmic rays, the researchers also learned that presolar grains often float through space stuck together in large clusters, "like granola", says Heck. "No one thought this was possible at that scale", Philipp Heck explained.

Scientists believe these discoveries will help to improve our knowledge of the galaxy and how it developed. "And when we know how many cosmic ray-produced helium and neon atoms we have, we can calculate an age, because the production rate is pretty constant over time". "It contains some of the oldest condensates in the solar system and also presolar materials".

Other reports by Click Lancashire

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