Asteroid strike

The dinosaur-killing asteroid hit the Yucatan Peninsula in Mexico

Science Photo Library / Alamy

The trajectory of the asteroid thought to have killed the dinosaurs 66 million years ago was just right to cause maximum damage. A new study of Chicxulub crater in Mexico, where the asteroid struck, has revealed that the angle and speed of the impact were probably in the perfect range to send clouds of choking vapour into the skies.

When an asteroid hits a planet, the resulting crater is highly dependent on the angle of the impact. Gareth Collins at Imperial College London in the UK and his colleagues compared a set of simulations with geological data gathered at Chicxulub crater to reconstruct that impact.

“That initial impact gouges a huge hole in the ground, which then collapses spectacularly and you form this huge overshoot, rather like what happens when you throw a pebble into the pond,” says Collins. In this “overshoot”, the middle of the hole bounces back up to create a plateau at the centre of the crater.

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In simulations of the Chicxulub impact, that central plateau was tilted toward the direction the asteroid came from, though how tilted it was depended on the angle of the impact.

The simulations that best matched observations of the crater were those where the asteroid came in relatively fast, around 20 kilometres per second, and hit the ground at an angle of around 60 degrees from horizontal.

Much of the devastation caused by the asteroid impact came from vaporised rock being blasted into the air and blocking out sunlight. It turns out that an impact angle of about 60 degrees is ideal for hurling as much vapour into the air as possible, Collins says – if it came in from straight overhead, the asteroid would have smashed up more rock but not sent as much into the atmosphere, and if it was more of a glancing blow, less rock would have been vaporised.

“It’s sort of a perfect storm,” says Collins, which is good news for us today. “This was a very bad day for the dinosaurs, and the more special the circumstances that had to come together to cause this event, the less likely that it’ll happen again.”

Journal reference: Nature Communications, DOI: 10.1038/s41467-020-15269-x

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