A comet from the edge of the solar system killed the dinosaurs: study

Sixty-six million years ago, a huge celestial object struck off the coast of what is now Mexico, causing a catastrophic “impact winter” that wiped out three-quarters of life on Earth, including dinosaurs.

A pair of Harvard astronomers say they have now solved long-standing mysteries surrounding the nature and origin of the “Chicxulub impactor.”

Their analysis suggests that it was a comet that originated in a region of icy debris at the edge of the solar system, that Jupiter was responsible for it slamming into our planet, and that we can expect similar impacts every 250 to 750 million years.

The duo’s article, published in the magazine Scientific reports this week, he rejects an older theory that the object was a fragment of an asteroid that came from the main belt of our solar system.

“Jupiter is so important because it is the most massive planet in our solar system,” lead author Amir Siraj told AFP.

Jupiter ends up acting as a kind of “pinball machine” that “propels these long-period incoming comets into orbits that bring them very close to the Sun.”

The so-called “long-period comets” come from the Oort cloud, which is believed to be a giant spherical shell that surrounds the solar system like a bubble that is made of chunks of icy debris the size of mountains or more.

Long-period comets take about 200 years to orbit the Sun, and they are also called solar scrapers because of how close they pass.

Because they come from the deep freezing of the outer solar system, comets are colder than asteroids and are known for the impressive traces of gas and dust they produce when they melt.

But, Siraj said, the evaporative impact of the Sun’s heat on solar scrapers is nothing compared to the enormous tidal forces they experience when one side faces our star.

“As a result, these comets experience such a great tidal force that the most massive of them would break into about a thousand fragments, each one large enough to produce a Chicxulub-sized impactor, or a dinosaur-killing event in the earth”.

Siraj and his co-author Avi Loeb, a science professor, developed a statistical model that showed the probability that long-period comets would collide with Earth, which is consistent with the age of Chicxulub and other known impactors.

The earlier theory that the object is an asteroid produces an expected rate of such events that was off by a factor of about ten compared to what was observed, Loeb told AFP.

‘A beautiful view’

Another line of evidence in favor of the comet’s origin is the Chicxulub composition: only about one-tenth of all asteroids in the main belt, which lies between Mars and Jupter, are made up of carbonaceous chondrite, while most of the kites have it.

Evidence suggests that the Chicxulub crater and other similar craters, such as the Vredefort crater in South Africa that was hit about two billion years ago, and the million-year-old Zhamanshin crater in Kazakhstan, all had carbonaceous chondrite.

The hypothesis can be tested by further studying these craters, those on the Moon, or even sending space probes to sample comets.

“It must have been a beautiful sight to see this rock approaching 66 million years ago, which was larger than the length of Manhattan Island,” Loeb said, although ideally we would like to learn how to track such objects and devise ways to deflect them if necessary.

Loeb added that he was excited about the prospect of the Vera Rubin Observatory in Chile coming online next year.

The telescope could see the interruption of the tides of long-term comets “and it will be extremely important to make forecasts for the next 100 years, to know if something bad can happen to us.”

Although Siraj and Loeb calculated that Chicxulub-like impactors would occur once every few hundred million years, “it’s a statistical question, you say, ‘on average, it is once in a while’ but you never know when the next one will come.” Loeb said.

“The best way to find out is to search the sky,” he concluded.

© 2021 AFP