A new study is questioning the origin of the body that smashed into Earth’s surface millions of years ago, causing a global extinction event that wiped out the dinosaurs. According to the research, the impactor may have originated from a massive sphere of icy matter that is thought to surround the solar system, known as the Oort cloud.
Around 66 million years ago, a massive chunk of cosmic debris known as the Chicxulub impactor struck Earth’s surface, triggering a mass extinction that ended the reign of the dinosaurs, and fundamentally altered the trajectory of life on our planet.
Many of the facts surrounding this cataclysmic event remain open to interpretation, including the origin of the Chicxulub impactor. One popular theory suggests that the wandering solar system body once orbited in the main asteroid belt, which is located between the orbits of Jupiter and Mars.
However, a new theory suggests that the Chicxulub impactor may have had a far more distant origin. According to a paper on the research, the impactor may instead have come from the Oort cloud – a diffuse sphere made up of trillions of pieces of debris that surrounds our Sun and all of the planets of the solar system.
Occasionally, some of the icy objects that make up the cloud get gravitationally disturbed, causing them to fall inward on a long, looping journey towards the Sun. Our solar system plays host to a massive number of these long-period comets.
In the new study, scientists from Harvard University used statistical analysis and gravitational simulations to show that a significant population of long-duration comets could be influenced by Jupiter’s gravity as they make their way inwards. These interactions force the icy wandering bodies into new orbits that take them much closer to the Sun. During the close approach, a type of gravitational perturbation known as tidal disruption may cause the comets to fracture, and put them on a trajectory that would cross Earth’s path.
"In a sungrazing event, the portion of the comet closer to the Sun feels a stronger gravitational pull than the part that is farther, resulting in a tidal force across the object," explains co-author of the new study Amir Siraj, an astrophysics undergrad at Harvard. "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."
The analysis revealed that roughly 20 percent of Oort-cloud-spawned comets become "sungrazers" after being disturbed by Jupiter’s gravity. Paired with the tidal disruption events, this would have increased the chances that pieces of the shattered comets would strike Earth’s surface by a factor of 10.
According to the study authors, the impact rate of tidally disrupted comet chunks striking the Earth syncs up with the timing of the Chicxulub mass extinction and other such crater-forming impact events.
"Our paper provides a basis for explaining the occurrence of this event," states study co-author Abraham Loeb, a Harvard astronomer. "We are suggesting that, in fact, if you break up an object as it comes close to the Sun, it could give rise to the appropriate event rate and also the kind of impact that killed the dinosaurs."
Evidence found at multiple sites – including the Chicxulub crater – which revealed that the impactor was a primitive form of carbonaceous chondrite meteorite, may also support the new origin theory. Carbonaceous chondrites are thought to be rare among the many wandering solar system bodies that populate the main asteroid belt between Mars and Jupiter. However, they could represent a common makeup for comets that originate from the Oort cloud.
Moving forward, the team intends to examine the remains of other impactors that formed craters on both Earth and its moon.
The paper has been published in the journal Scientific Reports.
