Earth’s meteorite collection just got called out for being a little biased—and what’s more, a team of astronomers pinpointed exactly why that bias occurs.
Carbonaceous asteroids are all over our solar system, both in the main belt and closer to Earth. But very few of the carbon-rich rocks are actually found on Earth, comprising just 4% of the meteorites recovered on our planet’s surface.
The astronomical team wanted to understand what causes the discrepancy. Their findings, published today in Nature Astronomy, indicate that carbon asteroids get obliterated by the Sun and Earth’s atmosphere before they can make it to ground.
“We’ve long suspected weak, carbonaceous material doesn’t survive atmospheric entry,” said Hadrien Devillepoix, a researcher at Australia’s Curtin Institute of Radio Astronomy and co-author of the paper, in a university release. “What this research shows is many of these meteoroids don’t even make it that far: they break apart from being heated repeatedly as they pass close to the Sun.”
The team analyzed nearly 8,000 meteoroid impacts and 540 potential falls from 19 different observation networks around the globe to understand why carbonaceous asteroids are so rare on Earth.
Carbonaceous meteorites on Earth give scientists the unique opportunity to study some of the oldest material in our solar system. But researchers also recover carbon-rich asteroid material from space; Japan’s Hayabusa2 mission and NASA’s OSIRIS-REx both plucked rocky material from distant asteroids and brought those samples to Earth, where they can be investigated to a fuller extent than remote observations allow.
“Carbon-rich meteorites are some of the most chemically primitive materials we can study—they contain water, organic molecules and even amino acids,” said Patrick Shober, a researcher at the Paris Observatory and co-author of the paper, in the same release.
“However, we have so few of them in our meteorite collections that we risk having an incomplete picture of what’s actually out there in space and how the building blocks of life arrived on Earth,” Shober added.
The team found that meteoroids created by tidal disruption events—when asteroids swing by planets closely enough to be broken apart by the planet’s forces—are particularly fragile, and survive atmospheric entry less than other types of asteroids.
Only the hardy carbon-rich asteroids make it to Earth, after surviving the Sun’s heat and the fiery burnup that occurs when entering Earth’s atmosphere. If astronomers want to get a proper assessment of the diversity of carbon-rich rocks, they’ll have to consider those that couldn’t survive the journey to Earth.
