This new insight into the asteroid that crashed into Chicxulub, in what is now Mexico’s Yucatan Peninsula, should help us better understand the history of celestial objects that have struck the Earth.

The debate over the nature of the asteroid that caused the extinction of the dinosaurs has been stirring scientists for decades, but a new study has just added a decisive stone to the edifice. This work, published Thursday, August 15 in the prestigious journal Sciencehave used an innovative technique to demonstrate that the culprit of the most recent mass extinction, 66 million years ago, formed beyond Jupiter. They also refute the idea that it was actually a comet.

This new insight into the asteroid that crashed into Chicxulub, in what is now Mexico’s Yucatan Peninsula, should help us better understand the history of celestial objects that have struck the Earth. “We can now say that this asteroid initially formed beyond Jupiter.”Mario Fischer-Gödde, lead author of the study and a geochemist at the University of Cologne, told AFP. A particularly interesting result, especially because this type of asteroid rarely hits our planet. And such information could prove useful for assessing a future threat, or even explaining the arrival of water on Earth, according to this researcher.

One of the few laboratories able to do this type of analysis

The new work is based on analysis of sediment samples formed 66 million years ago, which incorporated particles thrown around the world by the asteroid impact. The researchers measured isotopes—types of atoms—of a metallic chemical element called ruthenium. Ruthenium is absent from Earth’s sediments, so the scientists knew that the ruthenium they measured came from “100%” of the asteroid.

“Our laboratory in Cologne is one of the few” to be able to do this kind of analysis, Mario Fischer-Gödde stressed. And it was a first to study the Chicxulub asteroid or any other large celestial object that hit Earth, he added. Ruthenium isotopes make it possible to distinguish between the two major groups of existing asteroids: those of type C (carbonaceous), which formed in the outer solar system, and those of type S (silicates), formed in the inner solar system. The study concludes unequivocally that the asteroid responsible for the extinction of the dinosaurs was a type C asteroid, therefore formed beyond Jupiter.

A striking result

Previous studies had already made this hypothesis two decades ago, but with much less certainty. However, this result is striking, because the majority of meteorites – which are pieces of asteroids falling on Earth – are of the S type, underlines the geochemist. Does this mean that the destructive asteroid came directly from beyond Jupiter? Not necessarily, according to the researcher. “We can’t be really sure where the asteroid was just before it hit Earth.”he explained. After its formation, it may have stopped in the asteroid belt, located between Mars and Jupiter and where most meteorites come from, he said.

The study also refutes the idea that the object that struck Earth 66 million years ago was actually a comet (icy rocks evolving at the edge of the solar system). This hypothesis was put forward by a 2021 study that had caused a stir, but was based on statistical simulations. Analyses of samples now show that the object had a composition very different from a certain category of meteorite, carbonaceous chondrites, which are thought to have been comets in the past. It is therefore “unlikely” that the object in question was one, according to Mario Fischer-Gödde.

“We will have to be very careful”

To the question of the broader utility of these results, the geochemist offers two answers. First, better defining the nature of the asteroids that have struck our planet since its beginnings, some 4.5 billion years ago, could help solve the enigma of the origin of water on Earth, he believes. Scientists think that water could have been brought by asteroids, but rather C-type asteroids, like the one 66 million years ago, which nevertheless strike more rarely.

Going back in time also allows us to prepare for the future, according to the researcher. “If we find other mass extinctions” older ones are also “related to C-type asteroids”so if such an asteroid were to cross Earth’s orbit again one day, “We will have to be very careful”he says. “Because it might be the last we see.”