Sixty-six million years ago, a giant celestial object struck off the coast of what is now Mexico, causing a catastrophic “winter impact” that eventually wiped out three-quarters of life on Earth, including dinosaurs.
Two astronomers at Harvard say they have now solved long-standing riddles about 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 the crash on our planet, and that we can expect similar effects every 250 to 750 million years.
The duo’s paper, published this week in Scientific Reports magazine, contradicts an older theory that the object was a fragment of an asteroid that originated 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.
After all, Jupiter acts as a kind of “flipper” that “puts these arriving long-term comets into orbits that bring them very close to the Sun”.
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 made of icy fragments the size of mountains or larger.
The long-period comets take about 200 years to orbit the Sun and are also known as Suningers because of their proximity.
Comets are icier than asteroids and are known for the breathtaking traces of gas and dust they create when they melt, as they come from the deep freeze of the outer solar system.
But, Siraj said, the evaporative effect of solar heat on sunburners is nothing compared to the massive tidal forces they experience when one side is turned towards our star.
“As a result, these comets experience so great a tidal force that the most massive of them would break into about a thousand fragments, each of which fragments are large enough to create a Chicxulub-sized impactor or a dinosaur killing event on Earth.”
Siraj and his co-author Avi Loeb, professor of science, developed a statistical model that showed the likelihood that long-period comets would hit Earth, consistent with the age of Chicxulub and other known impactors.
The previous theory that the object is an asteroid creates an expected rate of such events that is a factor of ten compared to what was observed, Loeb told AFP.
“A beautiful sight”
Another proof of the comet’s origin is the composition of Chicxulub: only about a tenth of all asteroids in the main belt, which lies between Mars and Jupter, are made of carbonaceous chondrite, while most comets have it.
There is evidence that Chicxulub Crater and other similar craters, such as Vredefort Crater in South Africa, which was struck 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 on the moon or even sending space probes to take samples from comets.
“It must have been a beautiful sight to see this rock 66 million years ago, which was larger than the length of Manhattan Island,” said Loeb, although ideally we would like to learn to track such objects and find ways to distract them them if necessary.
Loeb added that he was thrilled with the prospect of the Vera Rubin Observatory in Chile opening up next year.
The telescope may be able to detect tidal disturbances from long-term comets. “It will be extremely important to be able to forecast the next 100 years to know if something bad could happen to us.”
Although Siraj and Loeb calculated that Chicxulub-like impactors would occur every few hundred million years, “it’s a statistical thing, you say, on average it keeps going, but you never know when the next one will come.” said Loeb.
“The best way to find out is to search the sky,” he concluded.
(Except for the headline, this story was not edited by GossipMantri staff and published from a syndicated feed.)