Oldest solid meteorite material found in Australia

A meteorite that fell in Australia back in 1999 has the oldest solid meteorite material found on Earth till date, proved a recent study.

The research indicates that stars are like phoenixes, after one dies, their dust and bits travel through space and eventually forms new stars, along with new planets, meteorites and satellites.

This study was contributed by researchers from the Field Museum, University of Chicago, Lawrence Livermore National Laboratory, Washington University, Harvard Medical School, ETH Zurich, and the Australian National University.

"This is one of the most exciting studies I have worked on," says Philipp Heck, a curator at the Field Museum, associate professor at the University of Chicago, and lead author of a paper describing the findings in the Proceedings of the National Academy of Sciences.

The materials Heck and his colleagues examined are called presolar grains-minerals formed before the Sun was born.

"They're solid samples of stars, real stardust," says Heck. These bits of stardust became trapped in meteorites where they remained unchanged for billions of years, making them time capsules of the time before the solar system.

But presolar grains are hard to come by. Theyare rare, found only in about five per cent of meteorites that have fallen to Earth, and they are tiny-a hundred of the biggest ones would fit on the period at the end of this sentence.

But the Field Museum has the largest portion of the Murchison meteorite, a treasure trove of presolar grains that fell in Australia in 1969 and that the people of Murchison, Victoria, made available to science.

Presolar grains for this study were isolated from the Murchison meteorite for this study about 30 years ago at the University of Chicago.

The researchers learned that some of the presolar grains in their sample were the oldest ever discovered-based on how many cosmic rays they'd soaked up, most of the grains had to be 4.6 to 4.9 billion years old, and some grains were even older than 5.5 billion years. For context, our Sun is 4.6 billion years old, and Earth is 4.5 billion.

But the age of the presolar grains wasn't the end of the discovery. Since presolar grains are formed when a star dies, they can tell us about the history of stars. And 7 billion years ago, there was apparently a bumper crop of new stars forming-a sort of astral baby boom.

"We have more young grains that we expected," says Heck. Their 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. There was a time before the start of the Solar System when more stars formed than normal.

This finding is ammo in a debate between scientists about whether or not new stars form at a steady rate, or if there are highs and lows in the number of new stars over time.

He goes on, "But thanks to these grains, we now have direct evidence for a period of enhanced star formation in our galaxy seven billion years ago with samples from meteorites. This is one of the key findings of our study."

Heck notes that this isn't the only unexpected thing his team found. As almost 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."

Heck and his colleagues look forward to all of these discoveries furthering our knowledge of our galaxy.

Heck notes that there are lifetimes' worth of questions left to answer about presolar grains and the early Solar System. "I wish we had more people working on it to learn more about our home galaxy, the Milky Way," he concluded.