How did the dinosaurs die? Harvard study shows monstrous comet, not asteroid, behind extinction

CAMBRIDGE, Mass. — While Hollywood movies might lead you to think the greatest threat to plant Earth is a giant asteroid floating in from outer space, a new study reveals a speeding comet may have caused one of the deadliest events in history. Researchers from the Center for Astrophysics, Harvard & Smithsonian say a large comet was likely spun around our solar system, eventually being sent like a piece of shrapnel into the Earth. The results of this planetary game of “pinball” wiped out the dinosaurs 66 million years ago.

Harvard researchers say this comet was likely tens of miles wide and originated from an icy sphere of debris at the edge of the solar system. Unlike asteroids, which consist of rock and metals, comets are balls of rock and ice which have their famous tails. Jupiter’s gravitational field, however, can send these giant snowballs off course — potentially turning them into deadly projectiles.

The dinosaur-killing space rock, the Chicxulub impactor, left behind a crater off the coast of Mexico that spans 93 miles and goes 12 miles deep. The devastating destruction ended the reign of the dinosaurs and wiped out almost 75 percent of the animal and plant species living on Earth.

The dinosaurs died in a game of ‘pinball’

The new study may reveal the origin and journey of this planet-killer; putting an end to centuries of debate. The object likely originated from that sphere of debris, the Oort cloud, before plummeting towards the sun.

The team theorizes that as comets slingshot around the sun, the gravitational forces rip at the side of the rock closest to the sun. Those tidal forces break off pieces of the rock, sending them like shrapnel through the solar system. Study authors say this puts an end to the popular theory that the Chicxulub impactor came from the asteroid belt sitting between Jupiter and Mars.

“The solar system acts as a kind of pinball machine,” astrophysics student Amir Siraj says in a university release. “Jupiter, the most massive planet, kicks incoming long-period comets into orbits that bring them very close to the sun.”

“It’s because of this that long-period comets, which take more than 200 years to orbit the sun, are called sun grazers,” Siraj adds. “In a sun-grazing event, the portion of the comet closer to the sun feels a stronger gravitational pull than the part that is further, resulting in a tidal force across the object. You can get what’s called a tidal disruption event, in which a large comet breaks up into many smaller pieces. And crucially, on the journey back to the Oort cloud, there’s an enhanced probability that one of these fragments hit the Earth.”

The calculations from Professor Avi Loeb and Siraj’s theory show that the chances of long-period comets impacting Earth increase by a factor of 10. About 20 percent of long-period comets become sun grazers.

A better explanation of the crater in Mexico

The pair claim the new rate of impact in their model is consistent with the age of Chicxulub, providing a satisfactory explanation for the crater’s origin.

“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,” says Prof. Loeb.

“Our hypothesis predicts that other Chicxulub-size craters on Earth are more likely to correspond to an impactor with a primitive (carbonaceous chondrite) composition than expected from the conventional main-belt asteroids.”

Spotting potential planet-killers flying through the solar system

The researchers say they believe this understanding is pivotal in case a comet threatens the Earth again. The new Vera Rubin Observatory in Chile may be able to see the tidal disruption of long-period comets after it becomes operational next year.

“We should see smaller fragments coming to Earth more frequently from the Oort cloud,” Prof. Loeb explains. “I hope that we can test the theory by having more data on long-period comets, get better statistics, and perhaps see evidence for some fragments. It must have been an amazing sight, but we don’t want to see that again.”

The findings were published in the journal Scientific Reports.

SWNS writer Joe Morgan contributed to this report.