The Solar System's oldest minerals reveal the Sun's violent past

Blue crystals hidden in space rocks open hidden secrets

meteorite

An analysis of hibonite, thought to be among the oldest minerals in the Solar System, has shown the turbulent and violent early history of our sun.

A team of scientists analysed meteorite samples containing hibonite using a scanning electron microscope and a mass spectrometer. The mineral contains small pockets of inert gases preserved from the chemical reactions from when the Sun’s energetic protons smashed into the calcium and aluminium atoms in the crystals.

"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," said Philipp Heck, co-author of the study and a curator at the Field Museum and a professor at the University of Chicago.

They formed when the young Sun was wrapped around an accretion disk full of gas and dust. The temperature would have been more than 1,500 degrees Celsius (2,732 Fahrenheit) and as the disk cooled, the blue hibonite crystals formed.

The elements making up the hibonite split apart to create neon and helium, which remained trapped inside for over 4.5 billion years. These crystals eventually got swept up into meteorites that eventually fell onto Earth.

“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. 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," said Levke Kööp, lead author of the paper published in Nature Astronomy and a postdoctoral researcher from the University of Chicago.

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The samples were first melted by heating with powerful laser beams. The gases released were then passed to a mass spectrometer to be analysed.

There was a surprisingly strong signal for helium and neon in the oldest minerals, which suggests that the newer material did not experience the same levels of radiation.

"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. 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," said Kööp. ®

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