A meteorite was holding a secret: Researchers recently discovered a tiny, ancient piece of the building blocks from which comets formed encased inside a meteorite, like an insect in amber.

The finding, published in Nature Astronomy, could offer clues to the formation and evolution of our Solar System, researchers from the Carnegie Institution for Science said.

The meteorite, the LaPaz Icefield 02342, was discovered in Antarctica’s LaPaz Icefield in 2002 and is a type of meteorite called a carbonaceous chondrite, which are rarely found on Earth.

Meteorites were once part of larger bodies, asteroids, which broke up due to collisions in space and survived the trip through Earth’s atmosphere. Their makeup can vary substantially from one meteorite to the next, reflecting their origins in diverse parent bodies that formed in different parts of the solar system.

Illustration how a sliver of cometary building block material was swallowed by an asteroid and preserved inside a meteorite. (Image Credit: Larry Nittler and NASA)

The LaPaz Icefield 02342 is a particularly pristine example with minimal weathering since its landing on Earth’s surface.

Asteroids and comets both formed from the disk of gas and dust that once surrounded the young Sun, but they aggregated at different distances from it, which affected their chemical makeup. Compared to asteroids, comets contain larger fractions of water ice and far more carbon, and typically formed farther from the Sun where the environment was colder.

Inside the LaPaz meteorite, Nittler’s team found a very carbon-rich slice of primitive material that bears some striking similarities to extraterrestrial dust particles that are thought to have originated in comets that formed near the Solar System’s outer edges.

Approximately 3-3.5 million years after the Solar System formed, but still long before Earth finished growing, this object — about one tenth of a millimeter (about four-thousandths of an inch) across — was captured by the growing asteroid from which the meteorite originated.

Using chemical and isotopic analysis of the material, Nittler and his team determined that the encased material likely originated in the icy outer Solar System along with objects from the Kuiper Belt, where many comets originate.

“Because this sample of cometary building block material was swallowed by an asteroid and preserved inside this meteorite, it was protected from the ravages of entering Earth’s atmosphere,” Nittler said. “It gave us a peek at material that would not have survived to reach our planet’s surface on its own, helping us to understand the early Solar System’s chemistry.”

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