Small fragment of a comet found inside a meteorite

A tiny building block from which comets were formed was discovered in a primitive meteorite. The discovery conducted by a team led by the Carnegie Institution of Science, including a researcher from Arizona State University, was published April 15 in Nature Astronomy.

The discovery could offer clues to the formation, structure, and evolution of the solar system.

"The meteorite calls LaPaz Icefield 02342," says Jemma Davidson, a researcher at the USS Meteorology Studies Center, at the School of Earth's Exploration and space. "The name comes from the place where it was found in the LaPaz ice field in Antarctica."

She adds that she belongs to a class of primitive carbonaceous chondrite meteors that have undergone minimal changes since their formation more than 4.5 billion years ago, probably beyond orbit. of Jupiter.

Construction debris

Meteorites were once part of larger bodies, asteroids, which crashed as a result of space collisions and survived the journey through the Earth 's atmosphere. Their composition can vary considerably from one meteorite to another, reflecting their origins in various parent bodies that have formed in different parts of the solar system.

Both asteroids and comets formed from the disk of gas and dust that once surrounded the young Sun, but they aggregated at different distances from it, affecting their chemical composition. Compared to asteroids, comets contain larger fractions of water ice and much more carbon. They usually form farther away from the Sun, where the environment was colder.

By studying the chemistry and mineralogy of a meteorite, researchers such as its lead author, Larry Nittler, of Carnegie, may reveal details about his training and the amount of heating and other chemical treatments that it has been the object during the solar system training years.

Candy with a surprise inside

Inside the LaPaz meteorite, Nittler's team discovered a slice of primitive material rich in carbon. It has striking similarities to the extraterrestrial dust particles that are thought to come from comets formed near the outer edges of the solar system.

About 3 to 3.5 million years after the formation of the solar system, but while the Earth was still growing, this tiny object – about a tenth of a millimeter – was captured by the growing asteroid at the origin of the meteorite.

"The primitive meteorites provide a snapshot of the early solar system that we can study in the lab," Davidson said. "The LaPaz meteorite is a good example because it has suffered minimal ground alteration."

Meteorites like LaPaz, she says, are great places to chase the presolar grains, microscopic pieces of dust stars formed by stars anterior to the solar system. But no member of the team also expected to find evidence of a surviving comet building block inside a meteorite.

Old survivor

"When Larry and Carles showed me the first electronic images of this carbon-rich material," Davidson said, "I knew we were looking for something very rare." It was one of those exciting moments for which you live as a scientist. "

By undertaking sophisticated chemical and isotopic analyzes of the material, Nittler and his colleagues, which include, besides Davidson, Conel Alexander of Carnegie, Rhonda Stroud and Bradley De Gregorio of the US Naval Research Laboratory, and Josep Trigo-Rodríguez, Carles Moyano-Cambero, and Safoura Tanbakouei from the Barcelona Institute of Space Sciences, in Catalonia, were able to show that the coated material probably came from the frozen outdoor solar system and objects from the Kuiper belt, where many comets are originating.

"Because this sample of cometary building block material was swallowed by an asteroid and preserved inside this meteorite, it was protected from the ravages caused by the penetration of the atmosphere into the Earth ", explains Nittler. "This gave us a glimpse of materials that would not have survived to reach the surface of our planet by themselves, helping us understand the chemistry of the primitive solar system."

The existence of this primitive material captured inside the meteorite suggests that because of the drag caused by the surrounding gas, particles like this have migrated from the outer edges of the solar system where comets and objects from the Kuiper Belt have formed, to the nearby area beyond. Jupiter, where the carbonaceous chondrites were formed. This reveals details of how the architecture of our solar system took shape during the early stages of planet formation.

"Discoveries like this demonstrate how important it is to recover valuable meteorites such as LaPaz from Antarctica," Davidson said. "We never know what secrets they will reveal."