Over 460 million years ago, one huge collision in the solar system produced many of the meteorites that still rain down on Earth. Researchers, for the first time, have probed the meteors that came before the asteroid collision, revealing that their composition is quite a far cry from those today.

Most of the meteorites seen today are quite rare, while many that are rarely seen today were much more common before the collision event, the scientists’ review discovered.

"Looking at the kinds of meteorites that have fallen to Earth in the last hundred million years doesn't give you a full picture," explained lead author Chicago’s Field Museum researcher Philipp Heck.

Meteorites From Ancient Past And Today

Meteorites are space rocks falling to Earth, formed from the debris of the collision of heavenly bodies such as asteroids and planets. The rarest meteorites detected today emerge from either differentiated or partially differentiated entities, namely huge dust and debris clusters that sizzle enough to form (or just partially) a core, mantle, as well as crust. Today it’s more common to find undifferentiated bodies, or a simple mix of dust, rock, and metal.

The new study revealed, however, that kind of meteorite, known as an ordinary chondrite, was much less common from its differentiated counterparts. For instance, 34 percent of the pre-collision meteorites belong to primitive achondrites, which today are only 0.45 percent of the meteorites landing on Earth. This lends further insight on more collisions in the solar system’s ancient past and therefore its evolution.

The team also saw micrometeorites originating from a billions-year-old collision at Vesta, or the most striking asteroid seen from Earth, as well as meteorites believed to hail from the birth of the Flora asteroid family about 1 billion years earlier.

Astounding Findings

The findings surprised not only the researchers but other planetary geologists not involved in the study.

“[It’s] incredibly inventive,” said Tasha Dunn of Colby College about using relict minerals in the rock record in order to determine the previous asteroid flux.

She added that the proportions of the types of meteorites raining down today do not match the asteroid belt populations, a puzzling point for scientists and among the biggest question marks in meteor studies.

Heck and his colleagues analyzed samples dating back from the targeted era, with its Russian and Swedish members using micrometeorites about 0.08 inches across. They sifted through rock samples from a Russian river valley that used to be seafloor.

In addition, they measured oxygen isotopes, or oxygen with varying numbers of neutrons, whose proportions tend to represent how distant from the sun the heavenly body formed.

In the future, the multidisciplinary effort seeks to delve on the different time windows to better understand earlier collisions, such as the blasted fragments from Vesta.

"Ultimately, we want to study more windows in time, not just the area before and after this collision during the Ordovician period, to deepen our knowledge of how different bodies in solar system formed and interact with each other,” Heck added.

The findings were discussed in the journal Nature Astronomy.

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