Evrim Yazgin
Cosmos science journalist
The Earth has been constantly hit by meteorites in its long life time, but scientists only now working out where they came from have found surprising results.
Previously, the origin of only 6% of meteorites was known. Scientists determined that this small fraction of meteorites came from the Moon, Mars and Vesta – one of the largest objects in the main asteroid belt which sits between the orbits of Mars and Jupiter.
New studies show that 70% of the 70,000 meteorites that have been found on Earth have come from 3 recent collisions in the main asteroid belt which sits between the orbits of Mars and Jupiter.
The research is reported 3 papers. The first is published in the journal Astronomy and Astrophysics, and another two papers are published in Nature.
The collisions occurred 5.8, 7.5 and 40 million years ago, according to the studies. They correspond to 3 young asteroid “families” known as Karin, Koronis and Massalia. These families formed from the destruction of asteroids at least 30km across.
These break ups explain the majority of meteorites currently falling to Earth.
Younger asteroid families have a large number of small fragments left over from the collisions that led to the asteroid group’s formation. Usually, these small pieces are also highly mobile, meaning they can escape the gravity of other objects in the asteroid belt and be flung into space.
Meteorites are made of chondrite. They come in different classes including carbonaceous chondrites (C chondrites – like those from the Moon and Mars), H chondrites and L chondrites.
H chondrites are the most common, making up about 40% of known meteorites. L chondrites are the next most abundant at 35%. But which groups of asteroids the H and L chondrites came from has remained a mystery until now.
According to the simulation, 37% of the meteorites come from the Massalia family. Some of these L chondrites are from a collision which took place about 40 million years ago. The Massalia family was also a source of much older meteorites when it experienced another collision about 450 million years ago, the researchers found.
The study also tracked the origins of asteroids which are a kilometre or more across. These are asteroids which could threaten life on Earth.
The new study was made possible by telescopic surveys of all the major asteroid families in the belt.
Among them are the recently sampled asteroids Ryugu and Bennu. The reveals that both came from the same parent asteroid which broke up to form the Polana asteroid family.
