Sungrazing comet may have caused dinosaur extinction event

Experts at Harvard University have proposed a theory that could explain the origin of the comet or asteroid that crashed into Earth about 66 million years ago, ultimately killing the dinosaurs.

Buried underneath the Yucatán Peninsula in Mexico, the Chicxulub crater is 93 miles wilde and 12 miles deep. The impact wiped out nearly three-quarters of the plant and animal species living on Earth.

The new Harvard study by Professor Avi Loeb and PhD student Amir Siraj may finally reveal the identity of the space object and how it ended up on a collision course with Earth. 

The researchers analyzed long-period comets from the Oort cloud, an icy sphere of debris at the edge of the solar system. They determined that a significant portion of these comets can be bumped off course by Jupiter’s gravitational field.

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

These so-called “sungrazers” can get broken apart into pieces of the rock and produce cometary shrapnel.

“In a sungrazing 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,” explained Siraj. 

“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 findings increase the chances of long-period comets impacting Earth by a factor of 10, and show that about 20 percent of long-period comets become sungrazers. According to the researchers, their new rate of impact is consistent with the age of Chicxulub, providing a satisfactory explanation for its origin and other impactors like it.

“Our paper provides a basis for explaining the occurrence of this event,” said Professor Loeb. “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 new theory may also explain why the Chicxulub crater had rock that was composed of carbonaceous chondrite. It is widely believed that the Chicxulub impactor originated from the main belt, which is an asteroid population between the orbit of Jupiter and Mars. 

However, carbonaceous chondrites are rare among main-belt asteroids, but may be widespread among long-period comets, which provides additional support for the new calculations.

The new Vera Rubin Observatory in Chile may be able to observe 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,” said Professor Loeb. “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.”

Professor Loeb said that understanding this is not just crucial to solving a mystery of Earth’s history, but could prove pivotal if such an event were to threaten the planet. “It must have been an amazing sight, but we don’t want to see that again.”

The study is published in the journal Scientific Reports.

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By Chrissy Sexton, Earth.com Staff Writer