The formation of the Solar System is only partially understood. Discovering tidbits about how the Sun and planets came to be is not an easy task, especially working out what the Sun was up to before any rocky planets formed. Luckily, researchers found some crucial clues trapped inside meteorites.
As reported in Nature Astronomy, researchers have discovered tiny hibonite crystals trapped inside meteorites that formed over 4.5 billion years ago. The composition of these ice-blue crystals shows all the signs of intense radiation, suggesting just how active the Sun was in the first few hundred million years after its formation.
"The Sun was very active in its early life – it had more eruptions and gave off a more intense stream of charged particles. I think of my son, he's three, he's very active too," co-author Philipp Heck, a curator at the Field Museum and a professor at the University of Chicago, said in a statement. "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."
The hibonite crystals contain calcium and aluminum atoms and when these are struck by high-energy protons, they split forming neon and helium that gets trapped within the crystal. The team used a powerful laser to melt the crystals and a mass spectrometer to measure their components. They detected a large signal for the presence of neon and helium.
This data shows that over 4.5 billion years ago the Sun must have been a lot more active than it is today. There must have been enough protons emitted by the Sun to create the amount of neon and helium witnessed when these crystals formed. The team thinks there is no other good explanation for this.
"In addition to finally finding clear evidence in meteorites that disk materials were directly irradiated, our new results indicate that the Solar System's oldest materials experienced a phase of irradiation that younger materials avoided," said lead author Levke Kööp, also of the University of Chicago and Field Museum. "We think that this means that a major change occurred in the nascent Solar System after the hibonites had formed – perhaps the Sun's activity decreased, or maybe later-formed materials were unable to travel to the disk regions in which irradiation was possible."
This evidence confirms what has long been suspected about the young Sun. Its effects might have played a role in the chemistry of the later Solar System and understanding them could help us figure out how our planet came to be.