A crater off the west coast of Africa likely originated from an asteroid impact around the much larger Chicxulub Crater. The giant asteroid that formed the Chicxulub Crater was the cause of the extinction of the dinosaurs.
The scientists who made the discovery acknowledge that further confirmation is needed. But this discovery raises the possibility of a double strike, caused by a previously split asteroid.
Less than 10% of the impact craters we know of are on the ocean floor. Seismic reflection studies from the Atlantic floor picked up structures of at least 8.5 kilometers buried beneath 300-400 meters of sediment.
In the journal Science Advances, the discoverers of the crater state that the crater is an impact crater that is millions of years old and dates back to the late Cretaceous.
This new crater is located in the Guinean Highlands, and is named after Nadir after a seamount located 100 kilometers to the south.
Not all craters come from impacts from outer space. However, the authors point out that Nadir's location, central peak and size ratio are inconsistent with alternative explanations such as volcanic collapse or salt withdrawal.
As a result, they argue the most likely explanation is that an asteroid (or possibly a comet) measuring about 400 meters in size landed at a depth of 800 meters.
We know the Earth experiences an impact of this magnitude more than once every million years, but the timing is perfect. The depth of the sediment places its age very close to Chicxulub Crater.
Interestingly, the discovery was made almost by chance. Dr Uisdean Nicholson of the University of Heriot-Watt was conducting a research project on seafloor spreading when he noticed something strange.
"I've interpreted a lot of seismic data in my time, but have never seen anything like it. Instead of the flat sedimentary sequence I expected at the highlands, I found a depression 8.5 kilometers below the seafloor, with very unusual characteristics. ," Nicolson said as quoted by IFL Science.
Drilling at the site can answer the question of whether Nadir was an impact crater, and add to the accuracy of the dating. Meanwhile, the authors discuss the implications if their judgment is correct.
"The impact would result in a tsunami over 3,000 feet high, as well as an earthquake with a magnitude of over 6.5," said Dr Veronica Bray of the University of Arizona in a statement.
The authors admit that it's possible the two impacts were pure coincidence, unrelated objects colliding close enough in time that we can't separate them.
Or, however, we may have been hit by a binary asteroid, perhaps formed through a previous collision with a smaller object or when a close encounter with the planet's gravity split it in two.
Such asteroids are common in space, but the paper notes that only 2-4% of known impact craters are binary structures.
The more complex scenario is that several major events in the asteroid belt affect large amounts of space rock so that many of them leave stable orbits and enter the inner Solar System.
Most of them would end up hitting the Sun or the inner planets if there were enough of them. We might expect some to hit Earth for over a million years or more.
"If we had found one 'brother' for Chicxulub, that would open up the question: is there another?," Bray said.