New study suggests dinosaurs killed by comet ripped apart by sun’s gravity
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TORONTO, Ontario (CTV News) — It’s a story we’re all familiar with: dinosaurs ruled the Earth until an asteroid sailed out of deep space and smashed into the planet, wiping out roughly 75 per cent of all life at the time.
Except, it might not have been an asteroid. A new study suggests the object that hit the Earth 65 million years ago could have been a fragment of a comet, torn off as the comet travelled too close to the sun.
And if this is true, the study says, there’s a higher likelihood that such a collision could happen again.
Published Monday in the Nature research journal Scientific Reports, the study looks at the origins of the Chicxulub impactor — the official term for whatever object it was that caused this specific mass extinction, named for a town in Mexico near the impact site.
In this new research, scientists with Harvard University simulated the gravitational interactions between comets, Jupiter, the Earth and the sun in order to estimate how likely it was for a comet to have been sling-shotted by Jupiter, the largest planet, towards the sun millions of years ago.
They suggest that comets from the Oort Cloud — a theorized collection of icy comets orbiting the sun as far as 3 light years away — that were sent too close to the sun by Jupiter’s gravitational pull could fracture and shower the Earth with debris big enough to wipe out entire species.
“In a sungrazing event, the portion of the comet closer to the sun feels a stronger gravitational pull than the part that is further, resulting in a tidal force across the object,” Amir Siraj, an astrophysics undergraduate student at Harvard, and one of the study’s principal authors, explained in a press release.
“You can get what’s called a tidal disruption event, in which a large comet breaks up into many smaller pieces. And crucially, on the journey back to the Oort cloud, there’s an enhanced probability that one of these fragments hit the Earth.”
It’s long been unknown whether the Chicxulub impactor was an asteroid or a comet, although the average person is generally more familiar with the tale of a massive asteroid.
Many theories have been proposed, but the origins still remain shrouded in mystery. The current prevailing theory, formed in 2007, is that the Chicxulub impactor was an asteroid that left the main asteroid belt in our solar system after a break-up of the Baptisina asteroid family.
The Baptisina asteroid family refers to a collection of asteroids that used to make up one massive asteroid called Baptisina. After Baptisina broke up into smaller parts, this so-called “family” followed a similar orbit for many years, gradually drifting farther apart, before many of the fragments broke out of the main asteroid belt between Mars and Jupiter and streamed towards Earth, several of them striking the Moon and Earth. The timeline that this occurred in matches up with the extinction of the dinosaurs, making it a strong possibility.
The Chicxulub crater itself has been studied, and evidence left behind in the crater has shed some light on what the giant object was made of.
It had a carbonaceous chondritic composition. This doesn’t rule out the Baptisina family or asteroids completely, but is rare among main-belt asteroids.
It is also incredibly rare for main-belt asteroids with a diameter of more than 10 metres and a composition of carbonaceous chondrite to strike the Earth, according to the new study, far too rare to account for the Chicxulub impact.
While it’s also rare for long-period comets — comets with an orbit greater than 200 years — to produce Earth collisions as large as the Chicxulub impactor did, it’s much more likely, researchers say.
The composition of comets has not yet been widely studied, but the only comet that has had samples taken from it to date shows a carbonaceous chondritic composition, which researchers say could be a sign that it is more widespread among comets.
If this new theory is correct, it ups the chances of long-period comets impacting Earth on such a catastrophic level by a factor of around 10. That’s still only one Chicxulub-size event per 250 – 730 million years, but it’s more than was thought could happen before. This theory puts comets and comet fragments at the same level of threat to the Earth as main-belt asteroids.
Other craters around the Earth have a similar composition as the Chicxulub crater, implying that more of our planet’s ancient wounds could’ve come from comets, such as the Vredefort crater in South Africa, the largest confirmed crater in Earth’s history.
More research needs to be done into the composition of comets, as well as these other craters, to give the theory more support. But researchers say this could be a crucial key to understanding what space events could threaten our planet in the future.
“We should see smaller fragments coming to Earth more frequently from the Oort cloud,” astronomer Avi Loeb, a professor at Harvard and the second author of the study, said in the release. ”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.”
Loeb added that “it must have been an amazing sight” when the Chicxulub impactor struck the Earth.
“But we don’t want to see that again.”
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