The space rock that doomed the dinosaurs was the shrapnel of a comet that flew too close to the sun, a Harvard study suggests.

About 66 million years ago, a space rock over 6 miles wide collided with Earth, hitting land that is now part of Mexico.

The impact sparked forest fires that spanned hundreds of kilometers, triggered a mile-high tsunami, and released billions of tons of sulfur into the atmosphere. This gaseous haze blocked the sun, cooling the Earth and damning the dinosaurs, as well as 75% of all life on the planet.

But the origins of this dinosaur-killer rock, named Chicxulub, have remained a mystery.

Most theories suggest that Chicxulub was a massive asteroid; hundreds of thousands of these rocks are found in a donut-shaped ring between Mars and Jupiter. But in a study published Monday, two Harvard astrophysicists suggested another idea: that Chicxulub was not an asteroid at all, but a shrapnel from an icy comet that had been pushed too close to the sun by gravity. of Jupiter.

Asteroids and comets are both classified as space rocks by NASA, but they differ in key ways: Comets form from ice and dust outside of our solar system and are generally small and move quickly, while rocky asteroids are larger, slower, and form closer to the sun.

“We suggest that in fact, if you break an object as the sun approaches, it could result in an appropriate event rate and also the type of impact that killed the dinosaurs,” Avi Loeb, astrophysicist and Harvard University cosmologist and co-author of the new study, said in a press release.

The solar system acts as a ‘flipper’ for comets

Most asteroids originate from the asteroid belt between the inner and outer planets of the solar system. But NASA scientists who monitor space objects passing close to Earth have yet to figure out where Chicxulub came from.

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In the new study, published in the journal Scientific Reports, Loeb and his co-author, Amir Siraj, suggest that Chicxulub did not come from the asteroid belt. Rather, they say it’s more likely to come from outside our solar system, in an area called the Oort Cloud.

Think of the Oort Cloud as a ring of trillions of frozen debris, which lies beyond the confines of the solar system, surrounding it. It is located at least 2000 times farther from the sun than the Earth. The comets that originate from the Oort cloud are known as long period comets because they take so long to complete an orbit around the sun.

But these comets can sometimes be pulled by the gravity of massive planets like Jupiter. Such an adjustment of a comet’s orbit could send it on a path much closer to the sun.

“The solar system is acting like a kind of pinball machine,” Siraj said in the statement.

Comets approaching the sun are called “sungrazers”. The new study calculated that about 20% of the comets in the Oort cloud are sungrazers. As our star approaches, its gravity begins to separate them. Fragments of a comet break off and may move towards neighboring planets.

This, say the study’s authors, is “a satisfactory explanation for the origin of the impactor” that killed the dinosaurs.

The asteroid versus comet argument is not settled

Siraj and Loeb aren’t the only scientists who believe that a comet, not an asteroid, has doomed dinosaurs. A group of researchers from Dartmouth College also suggested in 2013 that a high-speed comet could have created the Chicxulub crater.

Chicxulub hit Earth at a speed of 12 miles per second (43,200 mph), which is about 30 times faster than the speed of a supersonic aircraft. The resulting 100-mile-wide crater stretched 12 miles into the depths of the Gulf of Mexico. Some scientists have estimated that the power of the asteroid was equivalent to 10 billion atomic bombs used during World War II.

But not all researchers are convinced that a comet caused this destruction.

Natalia Artemieva, a senior researcher at the Planetary Science Institute in Arizona, told the New York Times that comet fragments from a sungrazer would have been too small to create the Chicxulub crater. And Bill Bottke, a planetary scientist from the Southwest Research Institute in Colorado, suggested that the study overestimates the frequency of sungrazers – and, therefore, the amount of fragments these comets produce.

Existing evidence supports the idea that Chicxulub was an asteroid, “but it’s inconclusive,” Bottke told The Times. “There’s still some wiggle room if someone really wants it to be a comet. I just think doing that case is really hard.”

Siraj and Loeb, however, said their theory was supported by a type of material found deep within Chicxulub Crater and other craters in South Africa and Kazakhstan. This substance, carbonaceous chondritis, can come from comets. While only 10% of the asteroids in the asteroid belt are made up of carbonaceous chondrites, the material “could potentially be prevalent in comets,” the study authors wrote.

The only samples ever taken from a comet in space were reported in 2006. They revealed that this object, called Wild 2, was composed of carbonaceous chondrite.

Finding the correct answer in the Chicxulub debate is helpful because it could help researchers determine the likelihood of a similar impact event in the future. According to one study, only two to three Oort Cloud comets have struck Earth in the past 500 million years. In contrast, according to the Planetary Society, an asteroid the size of Chicxulub strikes Earth every 100 million years or so.

Siraj and Loeb modeled the number of long period comets approaching the sun enough to scatter large fragments towards Earth. Their number suggests that 10 times more objects the size of Chicxulub have struck Earth in its history than scientists previously thought.

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