Astronomers Uncover the Origin of Most of Earth's Meteorites, Shedding Light on Our Solar System's Past | Smithsonian

Prior to the new research, scientists had traced the source of just 6 percent of the known meteorites that fell on our planet

Margherita Bassi

Daily Correspondent

Every day, 48.5 tons of meteoritic material hits Earth’s atmosphere. Almost all of it burns up during its descent, but the pieces that make it to the surface of our planet are called meteorites. Since some of those space rocks date back to the very early days of our solar system—and have remained unchanged since their formation—they can provide clues about the environment in which our sun and its planets came to be.

Up until recently, however, scientists had only traced the origin of 6 percent of the more than 70,000 known meteorites, linking them to the moon, Mars or Vesta (one of the largest asteroids in our solar system’s asteroid belt), per a statement.

Now, though, an international team of experts has identified the origin of more than 90 percent of all known meteorites, demonstrating that a staggering 70 percent came from just three asteroid families in the asteroid belt, which lies between the orbits of Mars and Jupiter. Their findings were presented in three papers published in the journals Astronomy and Astrophysics and Nature in September and October.

“It’s absolutely like a pot of gold at the end of a rainbow for a meteoriticist to know what asteroid the samples come from,” Sara Russell, a planetary scientist at London’s Natural History Museum who wasn’t involved with the new research, tells Science News’ Robin George Andrews.

The team studied the composition of meteorites found on Earth and conducted a telescopic survey of the materials that make up the major asteroid families in the asteroid belt. Via simulations, they modeled the formation of those asteroid families, per the statement.

An asteroid family “is a group of asteroids which have similar orbits because they were fragments created during a collision between two asteroids,” within the asteroid belt, Miroslav Brož, an astronomer at Charles University in the Czech Republic and lead author of two of the studies, explains to Reuters’ Will Dunham.

The three major asteroid families identified in the studies are called Karin, Koronis and Massalia. They formed as a result of three collisions 5.8 million, 7.5 million and about 40 million years ago, respectively. Those are recent origins, compared to the overall age of our solar system, which is about 4.6 billion years old.

“The most recent collisional events that happened in the asteroid belt are completely dominating the flux of material to our planet,” Michaël Marsset, a research fellow at the European Southern Observatory and lead author of one of the papers, tells Gizmodo’s Passant Rabie. “You might think that the meteorite flux should be a blend of all the compositional classes we observe in the asteroid belt, but it’s not at all the case, it’s dominated by three asteroids that fragmented recently.”

That makes sense, because younger asteroid families consist of more asteroid fragments because of their relatively recent formation, per the statement. These pieces collide with each other, in turn, which can sometimes knock the fragments onto a course toward Earth. Over tens of millions of years of these crash impacts, the cluster becomes depleted.

Researchers found that the Karin and Koronis families account for a type of meteorites called H chondrites, which make up 33 percent of Earth’s known meteorites, per Reuters. The Massalia family, on the other hand, is responsible for a type of meteorite called L chondrites, which make up 37 percent of Earth’s meteorites.

In all, chondrites make up 85 percent of the meteorites found on Earth. They are stony meteorites with distinctive round particles called chondrules, and they often contain olivine and pyroxene, silicate minerals commonly considered the building blocks of our solar system, as Trevor Ireland, a researcher at the University of Queensland in Australia, writes for the Conversation.

“Chondrites are primitive meteorites that have mostly preserved their original composition since their formation in our protoplanetary disk,” Marsset tells Reuters. Protoplanetary disks are rotating rings of gas and dust that surround stars at their birth and are hypothesized to lead to the creation of planets.

In other words, chondrites are the perfect meteorites to study for clues about the origin of our solar system.

Russell, however, is troubled at the thought of Earth’s meteorites representing such a limited sample of asteroids. “Maybe we’re only just seeing a tiny fraction” of the asteroid belt’s full bounty of material, she tells Science News. Perhaps scientists could learn more about the formation of the solar system if they had access to a broader range of meteorites.

There is a potential—and expensive—solution, Russell tells the publication: “We’ve got to have space missions to go out there.”

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Margherita Bassi | READ MORE

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.