In a scorching apocalyptic moment 66 million years ago, Earth was transformed from a lush haven into a nightmarish world with a fiery wound bleeding soot across the skies. The alien object that struck our planet sounded the death knell for dinosaurs and countless other species, even as its fallout opened up new niches for our mammal ancestors.
For decades, scientists have debated the identity of the impactor that struck our planet on that fateful day, leaving a 90-mile scar called the Chicxulub Crater under what is now Mexico’s Yucatán Peninsula.
Although an asteroid remains the primary contender, a team based at the Center for Astrophysics in Cambridge, Mass. Suggested that the culprit may have been an icy comet that was flying too close to the sun.
As long period comets from the far reaches of the solar system approach the sun, they can be torn apart by the star’s immense tidal forces. The resulting shards could have been catapulted into Earth orbit, providing “a satisfactory explanation of the origin of the impactor” that killed the dinosaurs, according to a study published Monday in Scientific Reports.
“To this day, the origin of the Chicxulub impactor remains an open question,” said Amir Siraj, an undergraduate astrophysics student at Harvard who led the research. His model, he said, examines “this special population of comets” that could have produced enough fragments – of the right size, at the right pace, and on the right trajectories – to threaten Earth “in a compatible way. with the current observation constraints. “
Other experts disagreed with the study’s methods and conclusions. “I believe their work has several inherent issues that go against their hypothesis,” said Bill Bottke, a planetary scientist at the Southwest Research Institute in Boulder, Colo.
From the perspective of Dr Siraj and his co-author, Harvard theoretical physicist Avi Loeb, a comet origin fills some of the gaps in our understanding of this ancient cataclysm, which caused the so-called KT extinction event , signifying the end of the Cretaceous period and the beginning of the Tertiary.
The researchers cite evidence that the impactor was made of carbonaceous chondrites, a rocky material found in a class of primitive asteroids dating back to the birth of the solar system. Samples returned from Comet Wild 2 in 2006 revealed evidence that the frozen world has a similar makeup, suggesting that this makeup “could potentially be prevalent in comets,” the researchers note in the study. The team speculates that Vredefort Crater in South Africa and Zhamanshin Crater in Kazakhstan could also be remnants of cometary impacts.
“The fact that long-lived comets are likely made up of the material – carbonaceous chondrites – that lies deep within these craters is in favor of our model,” Dr Loeb said.
The researchers say that including sun-burst comets in impact models increases the rate of dangerous objects at the Chicxulub scale by an order of magnitude, increasing the chances that Earth has been struck by a fragment of a comet 66 million years ago.
Natalia Artemieva, a senior researcher at the Planetary Science Institute in Tucson, Arizona, rejected this hypothesis of cometary origin. The four-mile-wide comet fragments envisioned by the study would have been too small to create the Chicxulub crater, she said. She noted the telltale spike of iridium that deposited as a result of the impact and is visible in geological strata around the world.
“The size of the projectile must be consistent not only with the size of the crater but also with the overall amount of iridium,” explained Dr Artemieva in an email. “This is certainly the case in the standard (stony asteroid) scenario, but not for a tiny cometary impact.”
Dr Bottke raised several concerns about the study. For example, he said, his model overestimates how often long-period comets would be separated by the sun and the number of dangerous fragments such encounters would produce.
While Dr Bottke is still not convinced that the impactor has a cometary origin, he noted that the asteroid’s explanation also raised many exciting and unresolved questions.
“The evidence we have for the KT impactor is more suggestive of asteroids than comets, but it is inconclusive,” said Dr Bottke. “There’s still some wiggle room if someone really wants it to be a comet. I just think doing this case is really hard.
Mr Siraj and Dr Loeb aren’t the only scientists to elicit visions of comets killing dinosaurs. Two geoscientists, Mukul Sharma of Dartmouth College and Jason Moore of the University of New Mexico, also put forward a hypothesis of cometary origin for the impactor.
“Assuming the modeling is correct, this article provides independent evidence for our claim in 2013 that a comet (high speed, small) and not an asteroid (slow, large) was hit 66 million years ago Dr. Sharma wrote in an email. “Our claim was based on geochemical and geophysical evidence, and so it is exciting to see this new research based on the modeling of cometary / asteroid motions.”
“As a scientist, it’s really important to keep re-evaluating your hypotheses,” said Dr Moore, adding that if the new paper stands up to “the scrutiny of the community at large, it would provide another incentive to review other existing data. sources and models with a cometary candidate in mind. “
Dr Siraj and Dr Loeb said future samples returned by comets may further shed light on their hypothesis. Sophisticated telescopes, like the one at the Vera C. Rubin Observatory, will also help scientists build a more comprehensive catalog of comets, asteroids and other near-Earth objects.
These advances will strain the theories about the source of the object that wiped out the dinosaurs and perhaps help humanity escape the same fate.
“Ultimately, the more we look to nature, the closer we can get to answering fundamental questions about the world around us – about the past, but also about the future,” Siraj said. “That’s the beauty of science.”