While more than 70,000 meteorites are known nowadays, only 6% were clearly identified by their composition as coming from the Moon, Mars, or Vesta - one of the largest asteroids in the main belt. The source of the other 94% of meteorites remained unidentified by now, when researchers from France, Czech Republic and the European Southern Observatory revealed that 70% of all known meteorite falls originate from three young asteroid families: Karin, Koronis and Massalia.
These families were formed by collisions in the main asteroid belt 5.8, 7.5 and about 40 million years ago. The Massalia family, in particular, has been identified as the source of 37% of known meteorites. The study was just published in Nature.
Why are these three young families the source of so many meteorites?
This can be explained by the life cycle of asteroid families. Young families are characterised by an abundance of small fragments left over from collisions. This abundance increases the risk of collisions between fragments and, coupled with their high mobility, their escape from the belt, possibly in the direction of Earth.
The asteroid families produced by older collisions, on the other hand, are sources of meteorites. The abundance of small fragments that once made them up has naturally eroded and finally disappeared after tens of millions of years of successive collisions and their dynamic evolution. Karin, Koronis and Massalia will inevitably coexist with new sources of meteorites from more recent collisions and eventually give way to them.
This approach has been extended to all meteorite families, revealing the primary sources of the carbonaceous chondrites and achondrites, which come in addition to those from the Moon, Mars, and Vesta. The small bodies from which the meteorites originated formed the building blocks from which today planets were created. They therefore participated in the chain of reactions that led to the appearance of life on Earth.
Tracing the origin of kilometre-sized asteroids threatening life on Earth
Thanks to this research, the origin of more than 90% of meteorites has now been identified. It has also enabled scientists to trace the origin of kilometre-sized asteroids (a size that threatens life on Earth). These objects are the focus of many space missions (NEAR Shoemaker, Hayabusa1, Chang'E 2, Hayabusa2, OSIRIS-Rex, DART, Hera, etc.).
The origin of the remaining 10% of known meteorites is still unknown. To remedy this, the team plans to continue their research, this time focusing on characterising all young families that were formed less than 50 million years ago.
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