Mystery crater potentially caused by relative of dinosaur-killing asteroid
How the crater may have formed. Credit: Author provided

The ocean floor is not explored as much as Mars. Our team of scientists discovered what appears to be an asteroid impact crater after mapping the seabed.

The crater is of the same age as the impact of the asteroid that wiped out the dinosaurs 66 million years ago.

There is a question of whether the crater is related to Chicxulub. It would be of huge general scientific interest as it would be one of a very small number of known marine asteroid impacts and so give new insights into what happens during such a collision.

As part of a larger project, the crater was identified using "seismic reflection." The pressure waves that are sent through the ocean and its floor are similar to the waves that are sent into the air. The data allows for the reconstruction of the rocks.

At the end of 2020 we found a very unusual feature. There was a large crater, a little under 10 km wide and several hundred meters deep, buried below several hundred meters of sediment.

The scale of the crater, the ratio of height to width and the height of the crater rim are all consistent with an impact. There are chaotic deposits outside of the crater floor that are similar to "ejecta", material ejected from the crater immediately after a collision.

The collapse of a submarine volcano or a pillar of salt below the sea were possibilities that we considered. There could be an explosion below the surface. None of these possibilities are compatible with the geology of the crater.

There were earthquakes and air blasts.

We built computer models of an impact event to see if we could recreate the crater and understand the impact.

For an asteroid 400 meters in diameter hitting an ocean that was 800 meters deep, the simulation is the best one. There are consequences of an impact in the ocean. With a large fireball visible hundreds of kilometers away, it would result in an 800-meter thick water column and the asteroid being instantly vaporized.

The impact would cause shock waves that would be equivalent to a magnitude 7 or 6.5 earthquake. There was a train of waves.

The air blast from the explosion would be louder than any recorded history has to offer. The energy released from the recent Tonga eruption would be a thousand times larger than the previous one. It is1-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-65561-6556

Mystery crater potentially caused by relative of dinosaur-killing asteroid
Nadir crater. Credit: Author provided

What is the relative status of the chicxulub?

One of the most intriguing aspects of this crater is that it is the same age as the giant Chicxulub event, which took place 66 million years ago. Maybe there is a relationship between them if this is an impact crater.

There are three possibilities as to their relationship. They may have formed from the break up of a parent asteroid, with the larger fragment resulting in the Chicxulub event and a smaller fragment forming the Nadir crater. The mass extinction event could have been worse if the Chicxulub impact had been added to.

The break-up could have been caused by an earlier near-collision when the asteroid or comet was close to Earth. There is a chance that the collision could have happened on a subsequent flight.

This pull-apart is what happened to the Shoemaker-Levy 9 comet when it collided with Jupiter in 1994.

It's possible that Nadir was part of a larger impact cluster that formed after a collision in the asteroid belt. The little cousin hypothesis is related to this.

This collision may have sent a shower of asteroids into the inner solar system, which may have collided with the Earth and other inner planets. When there were many impact events in a short period of time, we have a precedent for that.

This could be a coincidence. There is a chance of a collision of a Nadir-sized asteroid. We can't say for certain that the Nadir crater was formed by an asteroid impact until we recover samples from the crater floor. We submitted a proposal to drill the crater through the International Ocean Discovery program.

As with the main impact crater hypothesis, we can only test the little sister and little cousin hypotheses by dating the crater using samples and looking for other craters of the same age.

Could such an event happen soon? The size of the asteroid that we model is very close to the Bennu asteroid. The asteroid has a one-in-1,750 chance of colliding with Earth in the next couple of centuries, making it one of the most dangerous objects in the solar system.

More information: Uisdean Nicholson et al, The Nadir Crater offshore West Africa: A candidate Cretaceous-Paleogene impact structure, Science Advances (2022). DOI: 10.1126/sciadv.abn3096 Journal information: Science Advances

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