WASHINGTON: Meteorites _ rocks that fall to Earth from space _ have pelted our planet from its birth about 4.5 billion years ago to this day, often causing scant damage but sometimes triggering cataclysms.

But from where exactly are these space rocks coming? New research has the answer.

By studying the composition of meteorites that have landed over the years and the asteroids populating our solar system, astronomers have determined that about 70 per cent of known meteorite impacts came from just three groups of asteroids residing in our solar system’s main asteroid belt between Mars and Jupiter.

In total, the researchers in three different studies have now been able to account for the origins of most of the tens of thousands of known meteorites that have landed on Earth.

As part of the research, the astronomers carried out numerical simulations that enabled them to model the formation and evolution of families of asteroids orbiting the sun in the main asteroid belt.

“It is a group of asteroids which have similar orbits because they were fragments created during a collision between two asteroids,” said astronomer Miroslav Bro of Charles University in Prague, lead author of two of the studies, published in the journal Nature.

Collisions in the main asteroid belt send rocky fragments flying haphazardly through space, with some of those eventually striking Earth.

“While more than 70,000 meteorites are known, only six per cent had been clearly identified by their composition as coming from the moon, Mars, or Vesta, one of the largest asteroids in the main asteroid belt. The source of the other meteorites had remained unidentified,” said astronomer Michal Marsset of the European Southern Observatory in Chile, lead author of one of the two studies published in Nature.

The Massalia asteroid family, formed about 40 million years ago, accounts for a class of meteorites called L chondrites that represent 37 per cent of known Earth meteorites, the research found. The Karin family, formed 5.8m years ago, and the Koronis family, formed 7.6m years ago, account for a class of meteorites called H chondrites that represent 33 per cent of known Earth meteorites, it showed.

Another eight per cent of the Earth meteorites can be traced to the Flora and Nysa asteroid families in the main asteroid belt, the research found. And about six per cent of the meteorites can be traced to Vesta, it showed. Previous research found that less than one per cent of the meteorites came from Mars and the moon.

The researchers are still exploring the source of the remaining roughly 15 per cent of known Earth meteorites.

Space rocks have played a role in shaping the direction of life on Earth.

The new research did not look at the source of the one that struck Earth 66m years ago that wiped out the dinosaurs, aside from their bird descendants, and enabled mammals to become dominant. Another study published in August found that this object formed beyond Jupiter and probably migrated inward to become part of the main asteroid belt before being sent hurtling toward Earth, perhaps due to a collision.

Published in Dawn, October 18th, 2024