About 470 million years ago, two asteroids smashed into each other in outer space and shattered into multitudinous pieces. Many of those pieces rained down on Earth over the course of a million years as meteorites, and have become well-known by scientists. But the other space rock involved in the cosmic head-on collision has never been known – until now, thanks to the discovery of a meteorite that's never been seen before on our planet.

Researchers at the University of California Davis (UC Davis) found the meteorite, which they dubbed Ost 65, at a quarry in Sweden, a famous source for fossil meteorites, or those that have been chemically altered over time.

"Measuring just under four-inches wide, it looks like a gray cow patty plopped into a pristine layer of fossil-rich pink limestone," says a UC Davis report about the discovery. "The Ost 65 rock is called a fossil meteorite because the original rock is almost completely altered except for a few hardy minerals — spinels and chromite."

Spinel is a glassy mineral similar to rubies and chromite is an iron-containing mineral.

By analyzing the chromium and oxygen isotopes in those two minerals, the researchers were able to conclude that the meteor was "chemically distinct from all known meteorite types," according to UC Davis.

"In our entire civilization, we have collected over 50,000 meteorites, and no one has seen anything like this one before," said Qing-zhu Yin, UC Davis professor of geochemistry and planetary sciences. "Discovering a new type of meteorite is very, very exciting." Yin is the co-author of a paper detailing the find that appeared on June 14 in the journal Nature Communications.

Most of the particles that landed on Earth from the ancient collision are known as L-chondrites, a very common type of meteorite. But Ost 65 is a completely different kind of space rock.

To peg it to that long-ago asteroid smash-up, the researchers were able to determine that Ost 65 traveled in space for approximately one million years before landing in the quarry 470 million years ago – just like the L-chondrites. They made that determination by analyzing how long the newly-discovered meteorite had been exposed to cosmic radiation. The similar time signatures between the meteorites make it likely that they were involved in the ancient collision.

The historical period in which both Ost 65 and its more prominent rocky relatives rained down on Earth is known as the Ordovician Period – a time when nearly 100 times more asteroids smacked into our planet than today.

Yin says there may be even more types of asteroids that we've never encountered floating around in space, and that if we can find evidence of their having landed on Earth, we can better understand the early history of our solar system and planet. "If we can go back even further in time, we may eventually be able to find some of the true building blocks of Earth," he says.

Source: UC Davis