Where did the dinosaur-killing Chicxulub asteroid come from?

About 66 million years ago, a large asteroid (about 10-km-wide) crashed into Earth near Mexico creating a 180-kilometre-diameter impact structure. The event caused a mass extinction event wiping out 75% of all plant and animal species including non-avian dinosaurs.

Now, using computer modelling studies of asteroid evolution and data from known asteroids, a team from the US has investigated where the Chicxulub asteroid came from and how often such events have happened in the past. The results were published last month in Icarus.

“We decided to look for where the siblings of the Chicxulub impactor might be hiding,” said Dr  David Nesvorný, lead author of the study, in a press release. The team studied the main asteroid belt located between the orbits of Mars and Jupiter. According to NASA, this belt is estimated to contain between 1.1 and 1.9 million asteroids larger than 1 kilometre in diameter, and millions of smaller ones.

Using computer models, they studied how objects can escape from this belt and noted that thermal forces can allow these objects to drift and gravitational kicks from both the planets can push the object into orbits near Earth.

The team also used NASA’s Pleiades Supercomputer to model over 100,000 asteroids. The findings suggest that 10-km-wide asteroids from the outer half of the asteroid belt can strike Earth once every 250 million years on average. This is at least 10 times more often than previously calculated.

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“This result is intriguing not only because the outer half of the asteroid belt is home to large numbers of carbonaceous chondrite impactors, but also because the team’s simulations can, for the first time, reproduce the orbits of large asteroids on the verge of approaching Earth,” said Dr. Simone Marchi, co-author of the study. “Our explanation for the source of the Chicxulub impactor fits in beautifully with what we already know about how asteroids evolve.”

“This work will help us better understand the nature of the Chicxulub impact, while also telling us where other large impactors from Earth’s deep past might have originated,” Dr Nesvorný said.

Another paper published in February had suggested that the Chicxulub impactor came from the edge of the Solar System.

The two-member study team suggested that it originated from the Oort cloud, a sphere of debris at the edge of the solar system. The comet was then pushed off-course by Jupiter’s gravitational field and sent close to the sun, where it broke into several pieces. The team writes that these fragments cross the Earth’s orbit and hit the planet once every 250 to 730 million years or so.


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