“It must’ve been a beautiful view, but the fun ended when the rock hit the ground,” said study co-author Abraham Loeb, professor of science at Harvard University.
A comet is a piece of space debris made mostly of frozen gas, while an asteroid is a piece of rock most commonly found in the Asteroid Belt, a collection of asteroids between Mars and Jupiter, according to CNN weather correspondent Chad Myers.
The odds of an asteroid with a diameter of at least 6.2 miles causing a Chicxulub impact event is one in every 350 million years, according to the study. Long-period comets — comets with an orbit of more than 200 years — that are capable of the Chicxulub event are significantly rarer, with one occurring every 3.8 to 11 billion years, the study found.
The comet’s potential path
The researchers offer a scenario for how the comet could have beaten those long-shot odds.
As the comet traveled to the center of the solar system from the Oort Cloud, Jupiter’s gravitational force could have given it a boost so it had enough speed to reach the sun, according to Loeb.
“Jupiter acts just like a pinball machine,” Loeb said. “When something comes close to it, it can give it a kick.”
Upon reaching the sun, the sun’s gravitational force could have broken the comet into multiple pieces, he said. With more comet pieces, it’s 10 times more likely the comet would hit Earth as the pieces moved away from the sun, according to Loeb.
Other researchers disagree
Other researchers did not agree with the new study’s findings and still say several clues point to an asteroid creating the Chicxulub crater.
For one, Iridium — along with a handful of other chemical elements — was found scattered around the globe after the impact, said David Kring, principal scientist at the Lunar and Planetary Institute in Houston, who was not involved with the comet study.
Kring said the proportions of those elements are the same proportions seen in meteorite samples of asteroids.
The comet piece would have also been too small to make a crater of that size, said Natalia Artemieva, senior scientist at the Planetary Science Institute, who also was not involved in the study.
The study estimated the size of the comet piece to be about 4 miles wide, and Artemieva argued the comet would need to be at least 7.5 miles wide to make a crater the size of Chicxulub. With the small comet piece, she said, “it is absolutely impossible,” and the crater size from the impact would be at least half the size.
Kring also noted that how often an asteroid or comet hits Earth to create such an impact is statistically insignificant.
It doesn’t matter if it’s approximately “once every 350 million years and we had an event 66 million years ago,” because statistically, that would be the one occurrence in the 350-million-year time span, he said.
Researchers also have a plethora of asteroid samples to study compared to comets, Kring said.
“There’s absolutely no evidence that proves their model is incorrect, but on the other hand, there is a lot of evidence that is still pointing to an asteroid being the most likely impactor,” Kring said.
Loeb said he’s interested in searching for remaining comet pieces from the breakup to verify his theory.