Study: Dino-killer is not from the asteroid belt
66 million years ago, a huge celestial object struck off the coast of present-day Mexico, triggering a catastrophic “impact winter” that ultimately wiped out three-quarters of life on Earth, including dinosaurs.
Two Harvard astronomers say they have 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 its crash on our planet, and that we can expect similar impacts every 250 million to 750 million years ago.
The duo’s article, published in the journal Scientific reports this week pushes back an older theory that claims the object was a fragment of an asteroid from the main belt of our solar system.
Lead author Amir Siraj said, “Jupiter is so important because it is the most massive planet in our solar system.
Jupiter ends up acting as a kind of “pinball machine” which “sends these incoming long period comets into orbits which bring them very close to the Sun”.
So-called “long-period comets” originate from the Oort Cloud, thought to be a giant spherical shell surrounding the solar system like a bubble made of icy debris the size of a mountain or larger.
Long period comets take around 200 years to orbit the Sun and are also called sungrazers because of their proximity.
Because they originate from the deep freezing of the outer solar system, comets are more icy than asteroids and are known for the amazing trails of gas and dust they produce when they melt.
But, Siraj said, the evaporative impact of the Sun’s heat on the sungrazers is nothing compared to the massive tidal forces they experience when one side faces our star.
“As a result, these comets experience such a strong tidal force that the most massive of them would shatter into a thousand fragments, each of these fragments being large enough to produce a Chicxulub-sized impactor or destruction event. of dinosaurs on Earth. “
Siraj and his co-author Avi Loeb, a science professor, developed a statistical model that showed the likelihood of long-lived comets hitting Earth, which is consistent with the age of Chicxulub and other known impactors.
The previous theory that the object was an asteroid produced an expected rate of such events that was about a factor of 10 from what was observed, Loeb said.
‘A beautiful view’
Another evidence in favor of the comet’s origin is the composition of Chicxulub – only about a tenth of all the asteroids in the main belt, which lies between Mars and Jupiter, are made up of carbonaceous chondrite, while most of the comets have them.
Evidence suggests that the Chicxulub crater and other similar craters, such as the Vredefort crater in South Africa which was struck around 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 of the Moon, or even by sending space probes to take samples of comets.
“It must have been a wonderful sight to see this rock approaching 66 million years ago, which was greater than the length of Manhattan Island,” Loeb said, although ideally we would like to learn how to follow. such objects and find ways to deflect them. if necessary.
Loeb added that he was excited about the prospect of the Vera Rubin Observatory in Chile becoming operational next year.
The telescope might be able to see long-period comet tidal disturbance “and will be extremely important in making predictions for the next 100 years, to see if anything bad could happen to us.”
Although Siraj and Loeb calculated that Chicxulub-type impactors would occur once every few hundred million years, “it’s a statistical thing, you say, ‘on average it is every now and then. ‘but you never know when the next one is coming, “said Loeb.
“The best way to find out is to search the sky,” he concluded.