7-billion-year-old stardust is the oldest material ever found on Earth

The stardust existed long before our solar system and hitched a ride to Earth on a space rock.

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This is a fragment of the Murchison meteorite. The total mass of the meteorite's fragments collected is around 100 kg, or 220 pounds.

Field Museum

The Australian town of Murchison, Victoria, is home to fewer than 1,000 people but is one of the most important sites in the history of astronomy. In 1969, a huge meteorite fell to Earth, breaking up in the atmosphere and showering fragments of space rock south of the town. Decades later, researchers have discovered that locked inside those fragments were minuscule grains of stardust, the oldest material ever known to reach the planet. 

Researchers have found grains that are likely 5 billion to 7 billion years old -- older than our solar system, which formed about 4.6 billion years ago.

"This is one of the most exciting studies I've worked on," Philipp Heck, a geophysicist at the Field Museum of Natural History in Chicago and first author on a paper about the grains, said Monday in a statement

"These are the oldest solid materials ever found, and they tell us about how stars formed in our galaxy."  

The paper, published in the journal Proceedings of the National Academy of Sciences, details how Heck and other colleagues examined 40 grains of stardust that were taken from the Murchison meteorite three decades ago. To determine the age of the grains, they studied isotopes of the element neon, which interact with cosmic rays in space. The exposure to cosmic rays, which are high-energy particles that zip across the universe, creates these isotopes of neon. Seeing their abundance helped reveal the stardust's age.

The grains of stardust were pulled into the Murchison meteorite as it journeyed through space on its eventual collision course with the Earth. The majority of the stardust grains studied formed before our sun's birth around 4.6 billion years ago, and several are even older than 5 billion years. 

Because the stardust is so old, it can tell us more about space before our solar system had taken shape. 

"We have more young grains that we expected," said Heck. "Our hypothesis is that the majority of those grains ... formed in an episode of enhanced star formation. There was a time before the start of the solar system when more stars formed than normal."

Understanding the life cycle of interstellar dust is an important undertaking because it is a key ingredient in the cosmos and can be incorporated into asteroids as well as in stars and planetary systems.

The authors concede that their methodology -- using neon isotopes to age the grains -- does "suffer from relatively large uncertainties." But the research does provide more information on the formation and movement of interstellar dust and can also tell us more about star formation in the Milky Way.

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Originally published 12 p.m. PT