Quirks & Quarks

A comet fragment trapped inside a meteorite captures a time capsule of the early solar system

The surprising finding shows how material mixed as planets were forming

The surprising finding shows how material mixed as planets were forming

The 'LaPaz Icefield 02342' meteorite was found in Antarctica and had something special hidden inside. (Carlton Allen, NASA)

A tiny comet fragment from the outer edges of the solar system was found on Earth — inside a meteorite.

Scientists discovered a tiny blob of carbon about the width of a human hair inside a rocky meteorite discovered in Antarctica.

They think this speck of carbon is part of a comet that formed in the distant outer regions of our solar system and contains grains that are older than our Sun. It was trapped in a meteorite that landed on Earth, where scientists say it could help tell the story of the chaotic nature of our early solar system formation.

"It's like a fossilized piece of the outer solar system trapped in this meteorite," said Larry Nittler, a cosmochemist in the Department of Terrestrial Magnetism at the Carnegie Institution of Washington in D.C., in conversation with Quirks & Quarks host Bob McDonald.

Meteorites as time capsules

Meteorites land on Earth all the time. Most go unnoticed and many land in the oceans. But for researchers, a great place to find these space rocks is Antarctica, where the dark specks are obvious on the uniform white surface of the ice sheets.

Every year, a U.S.-funded meteorite hunting expedition heads to Antarctica and brings back hundreds of meteorites, each with a story to unlock about the formation of our solar system.

The arrow in this view of the LaPaz meteorite points to where the scientists found the carbon-rich comet fragment. The colours are produced polarized light shining through a thin slice of the meteorite; the grid lines are spaced one millimetre apart. (Carles Moyano-Cambero, Institute of Space Sciences, Barcelona)

Nittler and his team were doing a routine study of one of these meteorites, called "LaPaz Icefield 02342," when they found something special in it.

They did a chemical map of a thin slice of the object.

"One of my colleagues was looking at the maps and just said 'Oh my gosh, what's that?'"

Grains from outer realms

More detailed testing of the unusual inclusion revealed that it was quite different from the rest of the meteorite. In particular, it contained oxygen isotopes quite different from what is typically found on Earth, asteroids and other objects from the inner part of our solar system.

"It immediately told us that maybe this is not from the meteorite but from farther out in the solar system," said Nittler.

In fact, the oxygen isotopes more typically would be found in objects that formed before our solar system was created. Nittler said these presolar grains came from red giant stars or supernova explosions and were the raw material that eventually formed the solar system.

Along with the strange isotopes, the small object hidden in the meteorite was very rich in carbon. Meteors are made up largely of metals and rocky materials, whereas comets often have higher proportions of organic material, like carbon compounds.

Inside a meteorite, a carbon-rich section was found made of the material comets are built from. It is coloured red in this scanning electron microscope image. (Larry Nittler, Carnegie Institution for Science)

Based on the team's findings, this carbon blob is thought to have come from a comet that formed on the outer rim of our solar system, but then travelled into the solar system where it was trapped in an asteroid as it was forming.

They suspect that at some point part of that asteroid broke off and travelled to Earth as a meteor, protecting this tiny blob of presolar material with its hard rocky exterior.

Chaos in the Solar System

This may help illustrate the story of the chaos of the early solar system.

Scientists have previously found evidence that material from the inner solar system travelled to the outer solar system during the few million years when the solar system was forming. But there hasn't been much evidence that showed that this was also happening in reverse — material from the outer solar system travelling inward.

This tiny piece of a comet showed that material was going both ways. Nittler's team wants to find more evidence like this so they can further develop their understanding of how the solar system formed.

"I am eternally awed by the fact that I can study these rocks...take them apart and learn clues about these more exciting processes that happened billions of years ago. It just blows my mind," said Nittler.


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