Real Stardust: Scientists Find the Oldest Solid Material on Earth From a Meteorite
Sun, April 18, 2021

Real Stardust: Scientists Find the Oldest Solid Material on Earth From a Meteorite

Scientists claim they have found the oldest material on Earth: a piece of stardust from a meteorite that fell in Australia 50 years ago. They said the stardust formed about five billion to seven billion years ago, making the fragment older than our solar system / Photo by: Massimiliano Calamelli via Flickr

 

Scientists claim they have found the oldest material on Earth: a piece of stardust from a meteorite that fell in Australia 50 years ago. They said the stardust formed about five billion to seven billion years ago, making the fragment older than our solar system.

"This is one of the most exciting studies I've worked on," said Philipp Heck, the lead author of a paper describing the findings about the stardust. "These are the oldest solid materials ever found, and they tell us about how stars formed in our galaxy."


Studying the Ancient Interstellar Boulders

Dying stars spewed the stardust during its final stages, eventually reaching Earth on an asteroid that produced the 220-pound Murchison meteorite that fell in Australia in 1969. To determine the age of the ancient fragments, the researchers examined 40 "boulders" from Murchison, a town in the Tasman Region of the South Island of New Zealand.

Those "boulders" are presolar grains that the asteroid picked up as it passed through space. They were much bigger than the usual measurement of presolar grains; most measured about one micron, while the Murchison boulders ranged from 2 to 30 microns in length, reported Live Science, a science news website that features groundbreaking developments in science, space, technology, health, the environment, our culture, and history.

The researchers ground up bits of the meteorite and added acid, dissolving minerals and silicates to reveal the acid-resistant presolar grains. They then used a dating technique to measure the grains' exposure to cosmic rays during their billions of years of traveling in space.

Qatar-based media company Al Jazeera said 60% of the grains dated around 4.6 billion to 4.9 billion years ago while the oldest 10% dated more than 5.6 billion years ago. This finding suggested the dust fragments were the product of a star's birth in the Milky Way around seven billion years ago.

"And then it took about two to two-and-a-half billion years for those stars to become dust-producing," Heck said, noting that stars only produce dust "at the end of their lives."

The researchers admitted the findings were unexpected, especially with the other discoveries they unraveled, one of which was that their results supported earlier findings that suggested a dramatic increase in star formation seven billion years ago.

Scientists have long debated 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.

"Some people think that the star formation rate of the galaxy is constant. 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," Heck said, adding that this is one of the key findings of their study.

Real Stardust

Presolar grains are extremely rare and can only be found in about 5% of meteorites that have fallen to Earth. The Field Museum in Chicago has the largest portion of the Murchison meteorite. "They're solid samples of stars, real stardust," Heck said.

Meteorites are not as rare as presolar grains. NASA said there have been more than 50,000 meteorites found on Earth, 99.8% of which are from asteroids while the remaining 0.2% are either from Mars or the Moon.

Data from the Meteoritical Bulletin Database, the primary and official source for information about new meteorites shows that nearly all meteorites are found in deserts like Antarctica (4.7%) and the Sahara (18.4%).

Grinding and analyzing the ancient interstellar dust led to another discovery: "a pungent characteristic; it smells like rotten peanut butter," co-author Jennika Greer from the Field Museum and the University of Chicago said in a statement.

The dating technique used exposure age data to measure the grains' exposure to cosmic rays, some of which interact with matter and form new elements. Heck said the longer the stardust was exposed, the more those new elements form.

"I compare this with putting out a bucket in a rainstorm," the lead author explained. "Assuming the rainfall is constant, the amount of water that accumulates in the bucket tells you how long it was exposed."

Examining how the minerals in the grains interacted with cosmic rays also led them to discover that presolar grains usually travel in large clumps "like granola," Heck said, adding that no one thought it could be possible at such a scale.

The researchers believe these discoveries will help us further understand our galaxy. They said their study of directly determining the lifetime of stardust will hopefully be "picked up and studied so that people can use this as input for models of the whole galactic life cycle."

Learning a Stardust's Lifetime

There are still many questions about presolar grains and the early solar system that will take more than a lifetime to answer. Because of this, Heck said he wishes more people are studying and working on it to learn more about the Milky Way.
"I always wanted to do astronomy with geological samples I can hold in my hand," the lead author said.

"It's so exciting to look at the history of our galaxy. Stardust is the oldest material to reach Earth, and from it, we can learn about our parent stars, the origin of the carbon in our bodies, the origin of the oxygen we breathe. With stardust, we can trace that material back to the time before the Sun."

For Greer, learning about a stardust's lifetime is "the most interesting thing in the world" and getting them is the "next best thing to being able to take a sample directly from a star."

To learn more about our world, we need to look up to the stars.