The origin of 90% of all meteorites ever recovered has been discovered, thanks to a recent pair of papers.
By using observations of the asteroid belt and computer simulations, a team of planetary geologists revealed that over 70% of all known meteorites came from just three collisions in the main asteroid belt.
As the parent bodies broke apart during these collisions, it created vast numbers of smaller asteroids.
These create huge clouds of space rocks, known as asteroid families, which all share aspects of their orbit.
A team of international researchers led by astronomers from CNRS, the European Southern Observatory and Charles University looked at all the major asteroid families within the belt, taking detailed observations of them.
Using this information, they created detailed simulations to wind back the clock and discover when the collisions that initially produced them might have occurred, as well as which would have sent asteroids towards Earth.
The origin of most metoerites comes from just three families, they discovered.
One is the youngest asteroid family in the belt, Karin, which was created 5.8 million years ago and contains at least 90 known asteroids.
Another, the Koronis family, was created 7.5 million years ago and has 5,940 members, one of which – Ida – was visited by the Galileo spacecraft in 1993.
Finally, the oldest family is Massalia, created 40 million years ago. With over 6,000 asteroids making up the family, it is responsible for over 37% of all meteorites.
In addition, the simulations revealed the origin of several asteroids over 1km in size. While these would be large enough to threaten life on Earth should they strike us, none are on a collision course with our planet.
How did the collisions create so many meteorites?
Now the origin of meteorites has been discovered, the question becomes ‘why did they all come from just three collisions?’
The answer stems from asteroids within a family are much more likely to collide themselves.
As they share similar orbital properties, the asteroids are all relatively bunched up, meaning they are much more likely to run into each other.
Such impacts create yet more asteroid fragments, some of which would be thrown towards the inner Solar System and an eventual collision course with Earth.
This happens within all asteroid families, but over time the amount of collisions goes down as the number of small fragments is slowly depleted over a few tens of millions of years.
As these three families have not been depleted yet, they still incur a lot of collisions, sending meteorites our way.
How were the origin of meteorites discovered before?
The asteroids are fragments left over from when the Solar System was first created, and so by studying them astronomers can learn about the origins of Earth and our neighbouring planets.
While space agencies can mount missions to asteroids to take a look in-situ, meteorites deliver asteroid material directly to our planet’s doorstep.
Over the years, geologists and meteorite hunters have tracked down around 70,000 meteorites, with many ending up in scientific catalogues.
One of the first things to discover with any meteorite is it’s point of origin, as this provides much needed context for any future testing.
Around 6% of meteorites are known to hail from the Moon, Mars or Vesta, the largest asteroid in the main belt.
These are easy to identify because other space missions have uncovered their chemical composition, so by matching the chemical signatures the origin of these meteorites can be discovered.
On a few rare occasions, meteorites were recovered because they were seen entering Earth’s atmosphere in a bright fireball, as happened with the Winchcombe and Chelyabinsk meteorites.
Astronomers are able to trace back the trajectory of the incoming meteor to work out where in the Solar System it came from.
Of the remaining space rocks, the majority are ordinary chondrites – stony rocks which have never been part of a larger planetary body.
It’s these which are thought to mostly originate from the three collisions cited in the study.
The origin of the remaining 10% of meteorites is still unknown, but the team plan on extending their models back even further in time to see if they can find their origin.
