The statistical possibility of a long-period comet that is capable of striking the Earth and causing a mass extinction event is about one in every 3.8 billion to 11 billion years, the study says
Dinosaurs with a meteor
Dinosaurs with the asteroid
| Credit: Getty

Dinosaurs may have been killed off by a large piece of a comet, rather than an asteroid, a new study claims.

A pair of researchers at Harvard University now believe there is evidence that a piece of comet crashed into the Earth 66 million years ago to create the Chicxulub crater, according to a study published Monday in Scientific Reports.

The impact that created the 110-mile wide Chicxulub crater — located on the Yucatán Peninsula — is already thought to be the source of the mass extinction event that eradicated dinosaurs as well as most of the Earth's other species.

The new study uses statistical analysis and gravitational simulations to determine where the Chicxulub impactor (an asteroid or comet) came from, and how it came to strike Earth.

Chicxulub impact crater
Credit: NASA/Getty

Scientists have long believed that an asteroid caused the Chicxulub impact event, but researchers Avi Loeb and Amir Siraj suggest that a large piece of a long-period comet could have instead been the impactor.

A comet is a piece of space debris that is composed mostly of frozen gas, while an asteroid is a piece of rock. Asteroids are usually found in the Asteroid Belt, which is a group of asteroids between the orbits of Mars and Jupiter, according to CNN.

Comets are generally found further out in the solar system, past Jupiter's orbit and at farther distances from the sun, according to Scientific American.

The statistical possibility of a long-period comet capable of striking the Earth and causing the Chicxulub impact event is about one in every 3.8 billion to 11 billion years, the Harvard study says.

Loeb and Siraj theorize that a comet from the Oort cloud — a group of space debris at the edge of the solar system — was bumped off course by Jupiter's gravitational field, bringing it close to the sun.

"Basically, Jupiter acts as a kind of pinball machine," Siraj told The Harvard Gazette. "Jupiter kicks these incoming long-period comets into orbits that bring them very close to the sun."

These comets are called sun-grazers, he said.

"When you have these sun grazers, it's not so much the melting that goes on, which is a pretty small fraction relative to the total mass, but the comet is so close to the sun that the part that's closer to the sun feels a stronger gravitational pull than the part that is farther from the sun, causing a tidal force" he said.

"You get what's called a tidal disruption event and so these large comets that come really close to the sun break up into smaller comets. And basically, on their way out, there's a statistical chance that these smaller comets hit the Earth."

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The study says that once the comet is broken up by the sun, it is 10 times more likely to strike the Earth.

"Our paper provides a basis for explaining the occurrence of this event," Loeb told the Gazette. "We are suggesting that, in fact, if you break up an object as it comes close to the sun, it could give rise to the appropriate event rate and also the kind of impact that killed the dinosaurs."

The researchers suggest this theory could also explain the impactors that created the Vredefort crater — which is the largest confirmed crater in Earth's history — in South Africa two billion years ago and the Zhamanshin crater in Kazakhstan, which is the largest confirmed crater within the last million years.