This is part of the Murchison meteorite, a famous rock discovered on Sept. 28, 1969. (Photo: James St. John [CC by 2.0]/Flickr)
Fifty years ago a meteorite landed on Earth near Murchison, a rural village located in Victoria, Australia. Over the years, scientists have studied each crevice of the celestial rock.
Recently, a new team of researchers discovered stardust on the meteorite that dated back 7 billion years, making it the oldest known material on Earth.
"This is one of the most exciting studies I've worked on," said Philipp Heck, lead author of the paper describing the findings in PNAS . "These are the oldest solid materials ever found, and they tell us about how stars formed in our galaxy."
Stardust forms when stars burn out and pitch their particles into space, creating new planets, moons and meteorites.
Heck and his colleagues found presolar grains on the meteorite, which are minerals formed before the sun was born. And they are tiny — about 100 presolar grains would fit on the period at the end of this sentence.
This is a scanning electron micrograph of a presolar grain. It may not look like much, but it's rare — only found in about 5% of the meteorites on Earth. (Photo: Janaina N. Avila/Australian National University)
The stardust has remained trapped and unchanged for billions of years, making it a time capsule of space before our solar system was born.
Presolar grains are rare; they've only been found in 5% of the meteorites on Earth.
A large chunk of the Murchison meteorite was given to the Field Museum about 30 years ago, and since then University of Chicago researchers have isolated some of the solar grains.
"It starts with crushing fragments of the meteorite down into a powder," said Jennika Greer, a graduate student at the Fi eld Museum and the University of Chicago. "Once all the pieces are segregated, it's a kind of paste, and it has a pungent characteristic — it smells like rotten peanut butter."
The paste was then dissolved with acid until only the presolar grains remained and Heck and his team were able to determine their age and origin.
"We have more young grains that we expected," Heck said. "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. There was a time before the start of the Solar System when more stars formed than normal."
Stardust is the next best thing to taking samples directly from stars, allowing us to learn more about the history of our galaxy. Heck hopes the methods used in his team's research will help other scientists as well.
"With this study, we have directly determined the lifetimes of stardust," Heck said. "We hope this will be picked up and studied so that people can use this as input for models of the whole galactic life cycle."