Scientists Discover Surprising Origin of Most Meteorites that Strike Earth

About 466 million years ago, Earth was bombarded with a massive swarm of space rocks violently crashing on our planet, likely the result of a large asteroid breaking up into smaller fragments while traveling in orbit between Mars and Jupiter. The Massalia asteroid family, a population of asteroids that share similar orbits, may be the main culprit behind this massive infall. In fact, this particular asteroid family dominates nearly 40% of all meteorites that have fallen to Earth, with two other families of space rocks named as the source of most Earth-bound meteorites.

Thousands of meteorites have been recovered on Earth following a hectic journey through space. Now, new research is able to trace the origin of the majority of these fallen space rocks, suggesting that three young asteroid families are responsible for more than 70% of meteorites on Earth. The discovery is detailed in three studies published in Nature and Astronomy and Astrophysics, and the new findings could help scientists uncover mysteries of the early solar system.

The three asteroid families, Karin, Koronis and Massalia, formed through collisions in the main asteroid belt, specifically 5.8 million years ago, 7.5 million years ago, and 40 million years ago. That may seem like a long time ago to our feeble human brain, but it’s relatively recent compared to the age of the solar system (about 4.5 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, told Gizmodo. “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.” By “flux,” Marsset and his colleagues are referring to the flow of meteors that make their way from space to Earth.

Marsset explains that he wanted to trace the origin of the meteorites to resolve this discrepancy between the space rocks found on Earth and the ones observed in the asteroid belt. Up until now, researchers were only able to trace the origin of around 6% of meteorites, which primarily came from the Moon, Mars and one of the largest asteroids in the asteroid belt, Vesta. The source of the remaining rocks, however, was a mystery.

Using a telescopic survey of the composition of all the major asteroid families in the main belt, combined with computer simulations of the collisional and dynamical evolution of these major families, the scientists behind the recent discovery were able to reveal the primary source of most other meteorites. Based on the meteorites’ chemical composition, the researchers traced them back to their parent body, from which they broke off before landing on Earth.

“Such major collisions do not happen every day—every 30 to 50 million years sounds right as a frequency, although there were three major collisions over the past 8 million years or so,” Pierre Vernazza, a researcher at the French National Center for Scientific Research, and lead author of one of the studies, told Gizmodo.

Although the results are surprising, there might be a reason why the young asteroid families are dominating the flow of meteorite material to Earth. Younger asteroid families tend to have many smaller fragments left over from the collisions that caused their breakup. These fragments face a higher risk of colliding with each other, which can send some of the smaller debris hurtling toward Earth. “The collisional cascade inside these families is still active,” Marsset said. “That’s why they’re dominating this production of meteorites.”

Meteorites are tiny, rocky clues to mysteries of the solar system that happen to end up on Earth. Scientists can learn a lot by studying meteorites, allowing them to catch a rare glimpse of the early years of Earth and its neighboring planets.

“The meteorites have preserved in their present day composition a lot of information about our early protoplanetary disk,” Marsset said. “By linking these meteorites that we can study in fine details in our laboratory to specific families in the asteroid belt, we can reconstruct the original compositional gradient and thermal gradient of our protoplanetary disk. This ultimately is the goal of this kind of study. This is what we want to learn.”

Beyond tracing the origin of these space rocks, studying meteorites up close can reveal insights into the chaotic beginnings of our celestial neighborhood—and what might have happened millions of years before we arrived.