In one scorching apocalyptic moment, 66 million years ago, the earth was transformed from a lush refuge into a nightmare world with a burn wound soot flowing into the air. The extraterrestrial object that struck our planet spelled the damnation of dinosaurs and numerous other species, though its fallout opened up new niches for our ancestors of mammals.
Scientists have been debating for decades the identity of the impact that hit the planet on that fateful day, leaving a 90-mile scar called the Chicxulub crater under the present-day Yucatán Peninsula in Mexico.
Although an asteroid remains the leading candidate, a team based at the Center for Astrophysics in Cambridge, Massachusetts, suggested that the culprit was an icy comet that flew too close to the sun.
When long-term comets approach the sun from the outer corners of the solar system, they can be torn apart by the star’s large tidal forces. The resulting shards were possibly catapulted across Earth’s orbit, providing a satisfactory explanation for the origin of the impact ‘that killed the dinosaurs,’ according to a study published Monday in Scientific Reports.
“To this day, the origins of the Chicxulub impact remain an open question,” said Amir Siraj, an undergraduate astrophysics student at Harvard, who led the research. According to him, his model investigates’ this special comet population ‘that could produce enough shards – of the right size, at the right rate and on the right trajectories – to threaten the earth’ in a way that is in line with current observational constraints. ”
Other experts do not agree with the study’s methods and conclusions. “I believe their work has several intrinsic problems that work against their hypothesis,” said Bill Bottke, a planetary scientist at the Southwest Research Institute in Boulder, Colo.
From the perspective of mr. Siraj and his co-author, Harvard theoretical physicist Avi Loeb, a cometic origin fills a number of gaps in our understanding of this ancient catastrophe, which led to the so-called KT extermination event, which means the end of the Cretaceous and the beginning of the Tertiary.
The researchers cite evidence that the impact consisted 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 provided evidence that the icy world has a similar composition, suggesting that this composition ‘may be widespread in comets’, the researchers say in the study. The team speculates that the Vredefort crater in South Africa and the Zhamanshin crater in Kazakhstan may also be remnants of comic impact.
“The fact that long-term comets are likely to be made from the material – carbonaceous chondrites – that are deep in these craters supports our model,” said Dr. Loeb said.
The researchers argue that the fact that solar-splintered comets are included in impact models increases the rate of dangerous objects on the order of Chicxulub by an order of magnitude, increasing the chance that the Earth was hit by a comet fragment 66 million years ago.
Natalia Artemieva, a senior scientist at the Planetary Science Institute in Tucson, Ariz., Rejected this hypothesis of comet origin. The four-kilometer-wide comet fragments envisioned by the study would have been too small to create the Chicxulub crater, she said. She noted that the iridium peak deposited in the aftermath of the impact, and visible in geological layers around the world.
“The size of the projectile must not only correspond to the crater size, but also to the total amount of iridium,” said Dr. Artemieva explained in an email. “This is certainly the case in the standard (rocky asteroid) scenario, but not for a small comic impact.”
Dr. Bottke raised several issues with the study. He said, for example, that the model overestimates how long comets are pulled apart by the sun and how many dangerous fragments such encounters would yield.
Although dr. Bottke is not convinced that the impactor has a comic origin, he noted that the asteroid statement also raised many exciting and unresolved questions.
“The evidence we have for the KT impact points more to asteroids than comets, but it is not conclusive,” Dr Bottke said. ‘There’s another winding space if anyone really wants it to be a comet. I just think it’s really hard to make that case. ”
Mr. Siraj and dr. Loeb is not the only scientist to adorn visions of comets killing dinosaurs. Two geoscientists, Mukul Sharma of Dartmouth College and Jason Moore of the University of New Mexico, also hypothesized the impetus to be of comet origin.
“Assuming the modeling is correct, this paper provides independent evidence of our 2013 claim that a comet (high velocity, small) and not an asteroid (slow, large) affected 66 million years ago,” he said. dr. Sharma wrote in an email. . “Our claim was based on geochemical and geophysical evidence, so it’s exciting to see this new research based on the modeling of cometary / asteroidal motions.”
“As a scientist, it’s really important to reevaluate your hypotheses,” said Dr. Moore said, adding that if the new article resisted “examining the community as a whole, it would provide another incentive to revisit other existing data. Sources and models with a comet candidate in mind.”
Mr. Siraj and dr. Loeb said that future samples returned from comets could shed more light on their hypothesis. Sophisticated telescopes, such as those of the Vera C. Rubin Observatory, will also help scientists build a more comprehensive catalog of comets, asteroids and other near-Earth objects.
These advances would limit 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 at nature, the closer we can get to answering fundamental questions about the world around us – about the past, but also about the future,” he said. Siraj said. “This is the beauty of science.”