Although it's a relatively calm place today, the solar system had a pretty turbulent youth. After it sprung up about 4.6 billion years ago, the Sun was far more active in its early years, but we only really know this from studying other similar stars. Now, researchers have found the fingerprints of this active young Sun in tiny, bright blue crystals preserved in meteorites from a collection at Chicago's Field Museum.
Looking back to a time before the Earth had formed is tricky, but meteorites are the best places to find clues. These rocky fragments are effective time capsules of those early years, when the planets were forming out of a thick disk of dust and gas that surrounded the Sun. By cracking them open, scientists have previously found the ingredients for life, diamonds that hint at huge, long-lost planets, and even a strange stone that may have interstellar origins.
For the new study, researchers at the University of Chicago set out to find evidence of heightened solar activity from the beginning of the solar system. To do so, they investigated meteorites kept in the Field Museum that are loaded with tiny crystals that should have preserved chemical reactions from a more energetic Sun.
"The Sun was very active in its early life – it had more eruptions and gave off a more intense stream of charged particles," says Philipp Heck, one of the authors of the study. "Almost nothing in the solar system is old enough to really confirm the early Sun's activity, but these minerals from meteorites in the Field Museum's collections are old enough. They're probably the first minerals that formed in the solar system."
These minerals are what's known as hibonite, and when viewed under a microscope they show up as bright blue crystals that stand out among the dull backdrop of other grains. They naturally contain elements like calcium and aluminum, but charged particles from the Sun can change their composition, forming atoms of helium and neon. And these are exactly what the researchers were looking for.
"These crystals formed over 4.5 billion years ago and preserve a record of some of the first events that took place in our solar system," says Levke Kööp, lead author of the study. "And even though they are so small – many are less than 100 microns across – they were still able to retain these highly volatile nobles gases that were produced through irradiation from the young Sun such a long time ago."
To check for the presence of helium and neon, the team studied the hibonite crystals using a mass spectrometer and a laser. First, the laser melts a tiny grain of hibonite, then the mass spectrometer watches for any noble gases that are released as a result. Sure enough, the team detected huge signals of helium and neon, marking the first direct evidence of the Sun's rowdy early years.
The research was published in the journal Nature Astronomy.
Source: Field Museum
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