An old mystery solved: we now know where the asteroid that wiped out the dinosaurs came from

One spring day 66 million years ago, an object from space changed the face of the Earth forever. Its impact with our planet, comparable to billions of Hiroshimas, caused a fifteen-year “winter” and the gradual disappearance of 60% of species, including dinosaurs – with the notable exception of the ancestors of birds.

The culprit of the cataclysm is poorly understood. While the gigantic dimensions attributed to it are vague (around 10 km, with a large margin of error), we know that it left a crater 177 km in diameter around Chicxulub, in the Gulf of Mexico.

A neighbor or an intruder from far away?

These specialists had to decide between two options in the balance. Many asteroids orbit between Mars and Jupiter, not far from us: it would therefore have been likely that one of them left this belt following a collision with one of its peers and ended up approaching the Earth too dangerously.

It happens regularly that such objects cross the trajectory of our planet, while fortunately keeping a good distance. They are called near-Earth objects and we try to monitor them.

But other asteroids come from much further away in the Solar System, beyond Neptune, the planet furthest from the Sun, and their possible irruption in our vicinity is much less predictable because few are on our radar.

European samples of rare minerals

To solve the puzzle, the researchers looked at the remains of rare minerals that were spread across the Earth's surface after the impact. They outcrop in particular at three sites located in Denmark, Spain and Italy, samples of which were analyzed.

And the measurements were formal: the composition of the intruder is similar to that of carbon-rich asteroids that formed very far from us, well beyond Jupiter. “The projectile comes from the periphery of the solar system,” concludes Philippe Claeys, geologist at the Vrije Universiteit Brussel (Belgium) and co-author of the study.

Professor at the California Institute of Technology (United States), François Tissot, who also took part in the article, underlines that previous work already suggested this provenance, but that the technique used by his team leads to “more direct and less ambiguous results”: “New data will allow us to refine our understanding in detail, but there is now very little doubt as to the origin of the impactor that killed the dinosaurs.”

An “exceptional murderer”

Scientists have done the same work with five other impacts from the last 541 million years and all of them pointed, conversely, to asteroids in the belt between Mars and Jupiter. For us modern creatures, this is rather good news: the objects that hit the Earth and leave traces often seem to come from a region where they can be identified and followed, and, in the worst case, deflected! “This means that Chicxulub is completely abnormal,” says Philippe Claeys. “The dinosaur killer is exceptional in its provenance, for the moment.”

Lead author of the study, Mario Fischer-Gödde from the University of Cologne, Germany, would like to apply his method to another devastating episode for life, which occurred 252 million years ago and whose causes are still debated: “Perhaps in this way we could find out whether carbonaceous asteroid impacts have a higher probability of causing mass extinction events on Earth.”

As Philippe Claeys, who devoted his thesis and a large part of his career to Chicxulub, mischievously notes, “there are still plenty of impacts to study, enough to keep us entertained for a few years.”