Comet From Edge Of Solar System Killed Dinosaurs: study

Reuters, Washington

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

A couple of Harvard astronomers say that they have now resolved 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 on the edge of the solar system, that Jupiter was responsible for crashing into our planet, and that we can expect similar impacts every 250 million to 750 million years.

The duo's paper, published this week in the journal Scientific Reports, backslides against an older theory that claims that the object was a fragment of the asteroid that came from the Main Belt of our solar system.

"Jupiter is so important because it's the most massive planet in our solar system," Amir Siraj, the lead author, told Reuters.

The so-called "long-period comets" originate from the Oort cloud, thought to be a giant spherical shell that surrounds the solar system like a bubble made of icy pieces of debris the size of mountains or larger.

Long-term comets take about 200 years to orbit the Sun and are also called sungrazers because of how close they pass.

"As a result, these comets experience such a large tidal force that the most massive of them would shatter into about a thousand fragments, each of those fragments large enough to produce a Chicxulub size impactor or dinosaur-killing event on Earth."

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

Because they come from the deep freeze of the outer solar system, comets are icier than asteroids, and they are known for the stunning gas and dust paths they produce when they melt.

But, Siraj said, the evaporative impact of the Sun's heat on sungrazers is nothing compared to the massive tidal forces they experience when one side faces our star.

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

The previous theory of the object being an asteroid produces the expected rate of such events, which was a factor of about ten compared to what was observed, Loeb told Reuters.

"A worthy sight or delight?"

Another line of evidence in favor of comet origin is the composition of Chicxulub: only about one-tenth of all the asteroids in the Main Belt between Mars and Jupiter is made of carbonaceous chondrite, while most comets have it.

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

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

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

The telescope might be able to see the tidal disruption of long-period comets "and will be extremely important in making forecasts for definitely the next 100 years, to know if anything bad could happen to us."

Though Siraj and Loeb calculated Chicxulub-like impactors would occur once every few hundreds of millions of years, "it's a statistical thing, you say, 'on average, it's every so often' but you never know when the next one will come," said Loeb.

From the files of https://www.ndtv.com/world-news/comet-from-edge-of-solar-system-killed-dinosaurs-study-2372096