Sun's Activity Was Far More Intense Before Planets Formed, Ancient Meteorite Reveals

A team of researchers exploring an ancient meteorite has discovered that the heart of our solar system, the sun, was much more explosive than today when it came to life some 4.6 billion years ago.

Scientists have been studying the behavior of distant stars for years, revealing new and tantalizing facts about stellar evolution. However, as Earth came to be tens of millions of years after the birth of our star, there is no viable evidence to deduce what exactly happened when our sun was just a newborn star and there were no planets around.

The mystery has been there for long, but just recently, scientists from the University of Chicago found an evidence of sun’s extremely erratic early-life behavior, something pretty similar to a kid going through "terrible twos."

"The Sun was very active in its early life — it had more eruptions and gave off a more intense stream of charged particles,” Philipp Heck, one of the authors of the study, said in a statement.

Heck and colleagues came to this theory after analyzing the makeup of an ancient meteorite that crashed in Australia nearly half a century ago. The rock formed well before Earth came to be and carried extremely tiny crystals known as hibonites.

"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,” Heck added. “They're probably the first minerals that formed in the Solar System."

Scientists have long known that planets form in a disk of gas and dust around a young star. The same was the case of the sun, which probably had a disk heated up to 2700F. But, when this material started cooling, the first minerals, including hibonite, started forming inside space rocks. The crystal was rich in elements like calcium and aluminum and had a distinct icy blue hue.

As the hibonite crystals found in the Australian meteorite also carried very similar traits, the team decided to analyze its makeup in detail. They extracted a sample of the rock and used a mass-spectrometer and laser to understand its makeup. The mineral was melted, providing a signature of noble gases helium and neon.

The presence of these gases indicated that the sun was much more explosive than it is today. It blasted out huge solar flares, irradiating everything in its proximity, including the blue crystals found in this meteorite.

Due to this, solar flare particles — protons and other particles — interacted with calcium and aluminum atoms in the mineral and formed neon and helium isotopes, leaving them trapped for billions of years.

"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,” lead author Levke Kööp said in the statement. “And even though they are so small — many are less than 100 microns across — they were still able to retain these highly volatile noble gases that were produced through irradiation from the young Sun such a long time ago".

Such signs of irradiation were not observed in other, younger meteorites, which clearly suggests that the star grew quiet as things settled and Earth and other planets formed.

The study, titled "High early solar activity inferred from helium and neon excesses in the oldest meteorite inclusions," was published July 30 in the journal Nature Astronomy.