2024-08-15 21:29:00
This new insight into the asteroid that crashed in Chicxulub, in the present-day Mexican Yucatán Peninsula, should help to better understand the history of celestial objects that have struck the Earth.
The debate surrounding the nature of the asteroid that caused the extinction of the dinosaurs has stirred scientists for decades, but a new study has just contributed a key stone to the edifice. This work, published on Thursday, August 15, in the prestigious journal Science, used an innovative technique to demonstrate that the culprit of the most recent mass extinction, 66 million years ago, had formed beyond Jupiter. They also refute the idea that it was actually a comet.
This new insight into the asteroid that crashed in Chicxulub, in the present-day Mexican Yucatán Peninsula, should help to better understand the history of celestial objects that have struck the Earth. “Now, we can say that this asteroid initially formed beyond Jupiter,” said Mario Fischer-Gödde, the lead author of the study and a geochemist at the University of Cologne, to AFP. This finding is particularly interesting, especially since this type of asteroid rarely strikes our planet. And such information could prove useful in assessing a future threat or even explaining the arrival of water on Earth, according to this researcher.
One of the few laboratories capable of conducting this kind of analysis
This new work is based on the analysis of sediment samples formed 66 million years ago, which incorporated the particles thrown worldwide by the impact of the asteroid. The researchers measured the isotopes – that is, the types of atoms – of a metallic chemical element, ruthenium. This element is absent from terrestrial sediments, and scientists knew that the measured ruthenium came “100%” from the asteroid.
“Our laboratory in Cologne is one of the few” capable of conducting this kind of analysis, emphasized Mario Fischer-Gödde. And it was a first to study the Chicxulub asteroid or any other significant celestial object that has struck the Earth, he added. Ruthenium isotopes allow distinguishing the two main groups of existing asteroids: those of type C (carbonaceous), which formed in the outer solar system, and those of type S (silicaceous), formed in the inner solar system. The study unambiguously concludes that the asteroid responsible for the extinction of the dinosaurs was a type C asteroid, thus 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 to Earth – are of type S, the geochemist emphasizes. Does this mean that the destructive asteroid came directly from beyond Jupiter? Not necessarily, according to the researcher. “We cannot be really sure where the asteroid was just before it struck the Earth,” he explained. After its formation, it may have stopped in the asteroid belt, located between Mars and Jupiter, from where the majority of meteorites originate, he says.
The study also refutes the idea that the object that struck the Earth 66 million years ago was actually a comet (icy rocks evolving at the edges of the solar system). This hypothesis was put forward by a 2021 study that made headlines but was based on statistical simulations. Analyses of samples now show that the object had a very different composition from a certain category of meteorites, carbonaceous chondrites, which are believed to have been comets in the past. It is therefore “unlikely” that the object in question was one, according to Mario Fischer-Gödde.
“We must be very cautious”
When asked about the broader usefulness of these results, the geochemist offered two answers. First, better defining the nature of the asteroids that have struck our planet since its beginnings, about 4.5 billion years ago, could help to solve the mystery of the origin of water on Earth, he believes. Scientists think that water may have been brought by asteroids, but rather those of type C, like the one that struck 66 million years ago, which actually hit less frequently.
Looking back in time also allows for preparing for the future, according to the researcher. “If we find that other older mass extinctions” are also “linked to type C asteroids”, then if such an asteroid crosses the orbit of Earth again one day, “we must be very cautious,” he states. “Because this might be the last one we see.”