9km impact crater beneath the Atlantic reveals the dinosaur-killing asteroid had a friend

About 66 million years ago, a massive asteroid crashed into Earth. The Chicxulub impactor, as it is called, is known to have wiped out non-avian dinosaurs and left a huge crater on the edge of the Yucatán Peninsula – but it may not have acted alone. New research has found that during the same era, a second, smaller space rock struck our planet, creating a 9.2-kilometer (5.7-mile) crater deep beneath the Atlantic Ocean.

The Nadir crater was discovered in 2022. It is located off the coast of Guinea in West Africa and lies 300 meters (984 feet) below the bottom of the Atlantic Ocean. It is believed to have formed at the end of the Cretaceous period, about 66 million years ago, right around the time Chicxulub struck. However, the exact circumstances of how this came about remain uncertain to this day. Thanks to the new study that mapped the crater in unprecedented detail, researchers have finally confirmed how it formed.

Using high-resolution 3D seismic data, the team was able to determine “unambiguously” that the crater was created by an impact.

“This is the first time an impact structure has been fully imaged with high-resolution seismic data like this, and it is a treasure trove of information that will help us reconstruct the formation and evolution of this crater,” said study author Dr. Uisdean Nicholson wrote about the latest research in a Springer Nature blog post.

“There are about 20 confirmed ocean craters worldwide, and none of them have been recorded at anywhere near this level of detail. It is exquisite,” Nicholson added in a separate statement.

“One way to understand this is to think about a pregnancy ultrasound. A few generations ago, ultrasound showed a grainy spot. Now you can see the baby's facial features in incredible detail in 3D – including all internal organs. We went from fuzzy 2D imaging to amazingly high-resolution imaging of the nadir crater.”

From these extraordinary images, a clearer picture emerges of what happened 66 million years ago when the crater formed. For example, the team now knows that the asteroid itself was larger than previously thought, measuring about 450 to 500 meters (1,476 to 1,640 feet) wide. They also think it came from about 20-40 degrees northeast and hit Earth at a staggering 72,000 kilometers (44,700 miles) per hour – although this has yet to be verified with a new set of impact models.

Additionally, research has shed some light on the timing of events following the impact.

“After the impact and the formation of the central uplift, the soft sediments surrounding the crater flowed inward toward the evacuated crater floor, forming a visible 'rim.' The earthquake tremors caused by the impact appear to have liquefied the sediments beneath the seafloor throughout the plateau, resulting in the formation of faults beneath the seafloor,” Nicholson explained.

“The impact was also associated with large landslides as the edge of the plateau collapsed beneath the ocean. “In addition, we see evidence that a sequence of tsunami waves traveled away from the crater and then back toward the crater, with large resurgence scars preserving evidence of this catastrophic event.”

Researchers cannot yet date the event precisely, but are continuing their work on Nadir Crater to determine when it formed in the Late Cretaceous and its possible relationship to Chicxulub.

According to Nicholson, there has never been an impact of this magnitude in human history, and so it could be instructive to learn more about it – not just to learn more about what ended the reign of the dinosaurs, but about asteroid impacts generally understand.

“The closest person to have seen something like this is the Tunguska event of 1908,” Nicholson said. “The new 3D seismic data across the entire Nadir crater represents an unprecedented opportunity to test impact cratering hypotheses, develop new models of cratering in the marine environment, and understand the consequences of such an event.”

The study was published in Communications Earth & Environment.