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

Scanning electron microscope image of the 6.2-billion-year-old grain of silicon carbide from the Murchison meteorite. Image credit Heck et al doi 10.1073/pnas.1904573117

Scanning electron microscope image of the 6.2-billion-year-old grain of silicon carbide from the Murchison meteorite. Image credit Heck et al doi 10.1073/pnas.1904573117

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

The researchers studied minerals in the Murchison meteorite, a large space rock that disintegrated in 1969 above cow pastures in Murchison, Australia.

New analysis of dozens of presolar grains from the Murchison meteorite revealed a range of ages, from about 4 million years older than our sun - which formed 4.6 billion years ago - up to 3 billion years older than our sun, researchers reported in a new study.

Though the universe abounds with floating stardust, no presolar grains have ever been found in Earth's rocks.

"They're solid samples of stars, real stardust", said Philipp Heck, the lead author of a study on the particles and a curator at the Field Museum in Chicago, which acquired the largest pieces of the Murchison meteorite.

The stardust is made of grains of presolar silicon carbide, a mineral formed before our solar system was born.

"In order to explain our age distribution, where we have many more younger grains that we would otherwise expect, we have to explain this by this dust forming from more stars than normal", he said. But the grains the scientists analyzed for the study were much bigger, ranging from 2 to 30 microns in length. "With stardust, we can trace that material back to the time before the Sun". "We can see them with an optical microscope".

"But thanks to these grains, we now have direct evidence for a period of enhanced star formation in our galaxy 7 billion years ago with samples from meteorites".

"It's like burning down the haystack to find the needle", said Philipp Heck.

The researchers used a dating technique that measured the grains' exposure to cosmic rays during their interstellar journey over billions of years. In space, high-energy particles emanate from different sources, bombarding and penetrating solid objects that pass by.

"Some of these cosmic rays interact with the matter and form new elements".

By measuring how numerous new cosmic-ray produced elements are present in a pre-solar grain, scientists can tell how long it was exposed to cosmic rays, telling them how old it is.

"I compare this with putting out a bucket in a rainstorm". As long as the rain falls at a steady rate, you could calculate how long the bucket had been outside based on the amount of rain that it collects, Heck explained. "Our hypothesis is that the majority of those grains, which are 4.9 to 4.6 billion years old, formed in an episode of enhanced star formation". The researchers who identified the grains think many of them likely were created following a boom in star formation the Milky Way experienced some seven billion years ago.

However, the oldest yielded a date of around 7.5 billion years old. During most of its life, the star doesn't produce dust. "The stars only produce dust at the end of their lives".

This discovery supports findings by other astronomers that indicate a dramatic spike in star formation around 7 billion years ago, the researchers reported.

What's more, numerous grains weren't traveling through space alone; they journeyed as clumps, "almost like granola clusters", according to Heck.

For Dr Heck, this latest research is one of the most exciting studies he's worked on, but he's sure it won't be the last.

The cosmic ray method doesn't give us an absolute age of the stardust, said planetary scientist and meteorite hunter Phil Bland of Curtin University, who wasn't involved in the research.

As nearly a side note to the main research questions, the researchers also learned that presolar grains often float through space stuck together in large clusters, "like granola", Heck said.

Another meteorite that was recently added to the Field Museum's collection, the Aguas Zarcas from Costa Rica, or "cosmic mudball meteorite", was said to smell like cooked Brussels sprouts.

Notícias recomendadas

We are pleased to provide this opportunity to share information, experiences and observations about what's in the news.
Some of the comments may be reprinted elsewhere in the site or in the newspaper.
Thank you for taking the time to offer your thoughts.