Mysterious crater potentially caused by a relative of a dinosaur-killing asteroid
We considered other possible processes that could have formed such a crater, such as the collapse of an underwater volcano or a pillar (or diapir) of salt under the seafloor. An explosive release of gas below the surface could also be a cause. But none of these possibilities are consistent with the local geology or crater geometry.
Earthquakes, airblast, fireball and tsunamis
After identifying and characterizing the crater, we built computer models of an impact event to see if we could replicate the crater and characterize the asteroid and its impact.
The simulation that best matches the shape of the crater is of a 0.25 mile (400 meter) diameter asteroid hitting a 0.5 mile (800 meter) deep ocean. The consequences of an impact in the ocean at such water depths are dramatic. The result would be a half-mile column of water 800 meters thick, along with the asteroid and a substantial volume of sediment vaporized instantly – with a large fireball visible hundreds of miles away.
The shock waves from the impact would be equivalent to a magnitude 6.5 or 7 earthquake, which would likely trigger submarine landslides in the area. A train of tsunami waves would form.
The blast of air from the explosion is said to be larger than anything heard on Earth in recorded history. The energy released would be about a thousand times greater than that of the recent Tonga eruption. It is also possible that pressure waves in the atmosphere further amplify tsunami waves away from the crater.
One of the most intriguing aspects of this crater is that it is the same age as the giant Chicxulub event, roughly a million years ago, on the boundary between the Cretaceous and Paleogene periods ago. 66 million years old. Again, if this is really an impact crater, could there be a relationship between them?
We have three ideas as to their possible relationship. The first is that they may have formed from the burst of a parent asteroid, with the larger fragment resulting from the Chicxulub event and a smaller fragment (the “little sister”) forming the Nadir crater. If so, the adverse effects of the Chicxulub impact could have been added by the Nadir impact, exacerbating the severity of the mass extinction event.
The breakup event could have formed by an earlier near collision, when the asteroid or comet passed close enough to Earth to experience strong enough gravitational forces to pull it apart. The actual collision could then have occurred in a later orbit.
Although less likely for a rocky asteroid, this separation is exactly what happened to Comet Shoemaker-Levy 9 which collided with Jupiter in 1994, where multiple comet fragments collided with the planet for several days.
Another possibility is that Nadir was part of a longer-lived “impact cluster” formed by a collision in the asteroid belt earlier in the history of the solar system. This is called the “little cousin” hypothesis.
This collision may have sent a shower of asteroids into the inner solar system, which may have collided with Earth and other inner planets over a longer period, possibly a million years or more. We have a precedent for such an event in the Ordovician period – over 400 million years ago – when there were many impact events in a short time.