Mysterious Meteorite in Australia Points to Huge Undiscovered Asteroid

Meteorites aren't just beautiful to watch if you happen to catch them burning their way across the sky—they're also precious sources of scientific knowledge buoyed across the solar system like messages in bottles. And a recent analysis of one particular meteorite, known as Bunburra Rockhole, carries a message that packs quite a punch: We may be overlooking a large asteroid in our map of the solar system.

That's according to a paper published in the journal Geochimica et Cosmochimica Acta. In it, scientists analyzed a meteorite called Bunburra Rockhole, which fell to Earth on July 21, 2007, over Australia. When they first picked it up, scientists had thought it likely belonged to a large group of meteorites believed to have broken off Vesta, which is the second biggest asteroid in the ring of space rocks that falls between Mars and Jupiter. Meteorites from Vesta are identified by a unique oxygen fingerprint.

But when the team started looking more closely at Bunburra Rockhole, things started to get weird. First of all, the rock's entry had been caught on film, allowing scientists to trace its path—and that itinerary didn't match what they expected from a piece of Vesta. And when they looked for that trademark oxygen signature, it wasn't quite right. So they decided to take a closer look, running more tests on the rock.

01_05_meteorite_analysis_asteroid Analyzing meteorites (this is not the Bunburra Rockhole meteorite) allows scientists to learn about where they came from. Koen van Weel/AFP/Getty Images

The results of those tests let them form a new picture of where Bunburra Rockhole may have come from. First of all, they realized it's from the very inner edge of the asteroid belt, on the side close to Mars—closer to Mars than Vesta. But they also realized that in many ways, it still looked exactly the way they would have expected a meteorite from Vesta to look.

That led them to evaluate a few explanations: first, that the samples they tested had been contaminated. But they would have noticed that from looking at scans of the rock, so that theory went out the door. Then, they considered the possibility that Vesta is just a lot weirder than anyone thought, with compounds distributed in clumps so that two samples from different parts of the asteroid look like they're from two different asteroids. But that didn't make sense chemically.

Read more: Record-Breaking 2,000 New Asteroids Approached Earth in 2017 and Astronomers Expect to Spot Even More in 2018

Which left only one option: That Bunburra Rockhole really is just as new and weird as it seems. The team knows it's from a pretty large asteroid because of evidence of differentiation, when different ingredients start to settle into layers instead of forming one even mush. Beyond that, it's still a mystery.

“Either there is another big asteroid that we haven’t found yet,” lead author Gretchen Benedix, a geologist at Curtin University in Australia, said in a press release, “or the asteroid that Bunburra Rockhole originated from has evolved over time through space weathering and impact processing.”

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