The impact that wiped out the dinosaurs and brought about hell on Earth began at the mysterious edges of the solar system, scientists have said.
Scientists have long agreed that the dinosaurs were wiped out by the “Chicxulub impactor”, which left behind a vast crater off the coast of Mexico that is 93 miles across and 12 miles deep.
They have also agreed on the devestating horror that the impact would have wrought. It wiped out nearly three quarters of life on Earth, leaving the Earth in endless night and an 18-month winter filled with fire raining from the sky.
But what has been less clear is what that impact was actually caused by. Scientists do not know whether the object was a comet or an asteroid, where it originally came from, or how it came to strike Earth with such devastating force.
Answering that question does not only shed light on the end of the dinosaurs, but on the state of the solar system and our place within it, too, given the fear that we too could be hit by another mass extinction event.
New research – published today in the journal Scientific Reports, and written by scientists including Harvard’s Avi Loeb – attempts to anwer that question. By analysing data on the objects that fly around the solar system, as well as simulations of how gravity would push them around, they say they have found a way to explain how the Earth came to be hit with such devestating force.
They suggest that the journey of the object that wiped out the dinosaurs began in the Oort cloud, a shell of comets that sits at the edge of the solar system. A piece of comet was knocked off course by Jupiter’s gravity, they suggest, and sent it flying in towards the Sun, which broke the rock into pieces.
“Basically, Jupiter acts as a kind of pinball machine,” said Siraj, an undergraduate student who worked on the paper with Professor Loeb. “Jupiter kicks these incoming long-period comets into orbits that bring them very close to the sun.”
Such comets taken a considerable amount of time to get around the Sun – giving them the name sun grazers and long-period comets.
“When you have these sun grazers, it’s not so much the melting that goes on, which is a pretty small fraction relative to the total mass, but the comet is so close to the sun that the part that’s closer to the sun feels a stronger gravitational pull than the part that is farther from the sun, causing a tidal force” said Mr Siraj.
“You get what’s called a tidal disruption event and so these large comets that come really close to the sun break up into smaller comets. And basically, on their way out, there’s a statistical chance that these smaller comets hit the Earth.”
This story stands in opposition to one of the other main theories about where the impactor came from: that it was a piece of a bigger asteroid that came from the asteroid belt that runs between Jupiter and Mars.
The new paper suggests the object beginning its life in the Oort cloud is more feasible in part of its make-up. Research at the Chicxulub crater and other similar craters suggest the objects that caused them were relatively primitive objects called carbonaceous chondrites – such a composition is much more likely in Oort cloud objects than ones from the asteroid belt, the researchers say.
The researchers say that the hypothesis could be tested with further study of the craters themselves, including similar ones on the Moon.
When the Vera Rubin Observatory in Chile starts its work next year, scientists might also be able to watch long-period comets and see if they are behaving in such a way.
“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.”
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