A meteorite that fell in Australia 50 years ago contains the oldest solid material ever found on Earth: stardust.
The remnants of a celestial body that’s burnt up and died, cosmic dust eventually forms new stars, planets, moons, and meteorites.
The Murchison meteorite—so named for its landing place in Murchison, Victoria, Australia—fell to Earth in 1969.
Weighing in at 220 pounds, the well-studied space rock contains rare presolar grains: minerals formed before the Sun was born.
“This is one of the most exciting studies I’ve worked on,” according to Philipp Heck, a curator at the Field Museum, associate professor at the University of Chicago, and lead author of a paper describing the findings.
The bits of dust became trapped in meteorites, preserved in the solid time capsules for upwards of seven billion years.
“These are the oldest solid materials ever found,” Heck said in a statement. “And they tell us about how stars formed in our galaxy.”
Presolar grains—so tiny that a hundred of the largest ones could fit on the period at the end of this sentence—were isolated from the Murchison meteorite some 30 years ago at the University of Chicago.
“It starts with crushing fragments of the meteorite down into a powder,” Jennika Greer, a graduate student at the Field Museum and UChicago, and co-author of the study, explained.
“Once all the pieces are segregated, it’s a kind of paste, and it has a pungent characteristic,” she said. “It smells like rotten peanut butter.”
(A scent I am thankful to not recognize.)
That “rotten peanut butter meteorite paste” was then dissolved with acid, until only the presolar grains remains.
“It’s like burning down the haystack to find the needle,” Heck said.
Researchers then measured the grains’ exposure to cosmic rays to determine from what types of stars they came and how old they are.
Based on the number of cosmic rays they’d soaked up, most of the sample was declared 4.6 to 4.9 billion years old; some, however, were even more ancient—around 5.5 billion years.
For context, the Sun is 4.6 billion years old, while Earth is 4.5 billion.
But there’s one more thing.
Some 7 billion years ago, before the start of the Solar System, there was what the Field Museum called an “astral baby boom,” when more stars formed than normal.
“Some people think that the star formation rate of the galaxy is constant,” Heck said. “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.”
There are lifetimes’ worth of questions left to answer about presolar grains and the early Solar System, and researchers can’t resolve them all. Though Greer certainly wishes she could.
“Once learning about this, how do you want to study anything else?” she asked. “It’s awesome, it’s the most interesting thing in the world.”
Researchers can, however, dig deeper into the bizarre finding that stardust floats through space in large clusters, “like granola,” Heck said.
“It’s so exciting to look at the history of our galaxy,” he continued. “Stardust is the oldest material to reach Earth, and from it, we can learn about our parent stars, the origins of the carbon in our bodies, the origin of the oxygen we breathe.”
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