The Earth’s meteorite collection has just been accused of being somewhat biased – and what’s more, a team of astronomers has pinpointed exactly why.
Carbonaceous asteroids are found throughout the solar system, both in the main belt and closer to Earth. But very few carbon-rich rocks have actually been found on Earth, accounting for only 4% of all meteorites found on our planet’s surface.
The team of astronomers wanted to understand what causes this discrepancy. Their findings, published today in the journal Nature Astronomy, indicate that carbonaceous asteroids are being erased by the Sun and Earth’s atmosphere before they can reach the ground.
“We have long suspected that weak carbonaceous material does not survive in the atmosphere,” said Adrien Devilpoix, a researcher at Australia’s Curtin Institute of Radio Astronomy and co-author of the paper, in a university release. “This study shows that many of these meteoroids don’t even make it to the Sun: they break apart from repeated heating as they fly close to the Sun.”
The team analyzed nearly 8,000 meteorite impacts and 540 potential impacts from 19 different observing networks around the world to understand why carbonaceous asteroids are so rare on Earth.
Carbon meteorites on Earth give scientists a unique opportunity to study some of the oldest materials in our solar system. But researchers are also retrieving carbon-rich asteroid material from space; Japan’s Hayabusa2 mission and NASA‘s OSIRIS-REx have extracted rocky material from distant asteroids and brought these samples back to Earth, where they can be studied more fully 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 Schober, a researcher at the Paris Observatory and co-author of the paper, in the same release.
“However, there are so few of these in our meteorite collections that we risk having an incomplete picture of what is really going on in space and how the building blocks of life came to Earth,” added Schober.
The team found that meteoroids formed by tidal events – when asteroids fly by planets close enough to be broken apart by the planet’s forces – are particularly fragile and less likely to survive re-entry than other types of asteroids.
Only the hardy, carbon-rich asteroids make it to Earth, surviving the heat of the sun and the fiery combustion that occurs when they enter the Earth’s atmosphere. If astronomers want to get a proper estimate of the diversity of carbon-rich rocks, they will have to consider those that did not survive the journey to Earth.
