Artist's impression of the impact that occurred 65 million years ago that caused the Chicxulub crater and undoubtedly caused the extinction of the dinosaurs.
D. AVIS / CAMBRIDGE PRESS
66 million years ago, a huge object struck the Earth, causing the extinction of a majority of life, including that of dinosaurs.
This object was previously thought to be an asteroid, but a new study supports a different theory.
It would have actually been a fragment of a comet, coming from the confines of the solar system.
About 7 km large, this piece would have come from the explosion of a comet from the Oort cloud, a "debris cloud" located at the edge of the solar system, according to the study published this Monday in the journal
Comets exploded near the Sun
Before coming to crash on Earth, this comet would have been pushed towards the Sun by the gravitational attraction of Jupiter.
The largest planet in our system would have acted like a "pinball machine", sending the comet back into "orbits bringing it very close to the Sun," said Amir Siraj, lead author of the study and an astrophysics student at Harvard.
Faced with the immense force of attraction of the Sun, the largest comets would have burst "in more than 1,000 fragments", according to the astrophysicist.
Each of the fragments, one of which would have been catapulted to Earth, would have been "potentially large enough to cause an event like the one that killed the dinosaurs."
A higher impact frequency for comets
Until then, the most popular theory was that the object responsible for the extinction of the dinosaurs came from the main asteroid belt, located between Mars and Jupiter.
But according to Avi Loeb, co-author of the study and professor at Harvard, the frequency with which these asteroids can hit Earth is "at least ten times too low" to explain the impact.
"Asteroids have a slightly higher impact frequency [than comets], so they are favored" to explain the disappearance of dinosaurs, notes Amir Siraj.
But the explosion of comets multiplies the number of flying objects.
“Potentially, fragments of even more massive comets (…) can explain this frequency”, according to the researchers.
Study the impact of future comets and asteroids
Another clue goes in their direction: the impact crater was caused by an object made of carbonaceous chondrite.
However, only around 10% of asteroids have them, while comets have more.
In 2022, the new telescope at the Vera Rubin Observatory in Chile should make it possible to observe the gravitational pull on comets.
An opportunity that excites the two researchers of the study.
This "will be extremely important in forecasting the next 100 years, to know if anything bad could happen to us."
According to them, a comet fragment could strike the Earth at a frequency of several hundred million years.
No short-term threat, therefore, especially compared to asteroids.
However, nuance Avi Loeb, "it is about a statistic".
“You never know when the next one will arrive,” he concludes.
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