?It can’t have been a comet«

In early 2022, US researchers published a widely acclaimed paper in »Scientific Reports«. In the article, the alleged sudden decline of the Hopewell culture – a civilization that had spread along the rivers in the mid-western and north-eastern parts of North America – was attributed to a comet that had supposedly hit the continent around 1,600 years ago. While this theory garnered a great deal of media attention, an objection has since been raised in the same journal by astrophysicist Prof. Ralph Neuhäuser from the University of Jena and anthropologist Dagmar L. Neuhäuser. In our interview with Ralph Neuhäuser, he explains what it’s like to have to correct fellow researchers’ scientific errors, which had all the makings of a Hollywood film.

Interview by Sebastian Hollstein

What did Kenneth Tankersley and his team of anthropologists base their hypothesis on?

Tankersley and his team conducted geophysical examinations in former Hopewell settlements near Cincinnati, Ohio. They found a large number of meteorite fragments and an increased occurrence of platinum and iridium, which were allegedly of extra-terrestrial origin. They considered scorch marks that were around 1,600 years old to be the result of an air burst, when an object explodes after entering the Earth’s atmosphere, and proposed the hypothesis that a comet had exploded over the area at the time.

They attempted to substantiate this theory with historical and cultural evidence, firstly arguing that a large number of comets are said to have come very close to the Earth in the third and fourth centuries AD, as observed by contemporary Chinese astronomers. Secondly, they interpreted artificially created mounds to be a reconstruction of a comet with its characteristic tail. And thirdly, narratives found in the oral tradition of various North American peoples were cited as evidence.

Why do you think that can’t be correct?

In our response, we focused on the non-geophysical aspects we are qualified to assess, which were the decisive factor proposed in the comet hypothesis. But none of the evidence presented points to an air burst caused by a comet.

When claiming that there had been a large number of comets near the Earth during this period, the researchers cited a paper from the 1930s, but this assertion is not reflected in the paper at all. All of the more recent editions and works published in the past decades also show that there were by no means more comets during the period in question – let alone more comets close to the Earth. The sources dating from the period in question, such as the observations documented by the Chinese court astronomers, do not contain any evidence of a large, bright (near-Earth) comet that suddenly disappeared (by entering the Earth’s atmosphere) – and this would have surely been visible to them and worth mentioning. Furthermore, the mounds of earth cited in the paper, stylized into the shape of a comet, are only a small part of a much larger structure, and the researchers do not explain how the remaining segments of the structure fit into their line of reasoning.

The traditional narratives referenced, whose origins cannot be precisely dated, can also be interpreted in a completely different way. For example, the story of »The Day the Sun Fell from the Sky« could also refer to a solar eclipse. The researchers did not take a holistic view of the historical and cultural traditions.

What motivated you to write your own paper refuting the hypothesis proposed by the US researchers?

This is a topic that concerns our field of work and our expertise: the interpretation of historical celestial observations from various cultures for use in modern science. We work in a transdisciplinary team. We thought the hypothesis was questionable and supported by false arguments. In that case, it’s our job to raise an objection.

Specifically, no clear evidence – not even geophysical – was presented to prove the occurrence of a comet. A comet is essentially a huge, dirty snowball, and the metals found on the ground can hardly be traced back to such an incident. It is extremely rare for a comet to enter the Earth’s atmosphere – not a single case has been recorded in human history – so a hypothesis like that would have to be supported by solid evidence. If the decline of the Hopewell culture can really be traced back to an extra-terrestrial event, then it was probably an asteroid.

Did you make the researchers aware of your reservations?

Yes, we put forward our counter-arguments in a letter and received a rather reserved response. We then also submitted our paper to »Scientific Reports« for publication in the »Matter Arising« section, which is intended for corrections of this kind. The journal put six reviewers on the case, which is very unusual – it’s normally only half as many. Five of them agreed with us and even provided further geophysical counter-arguments, and the sixth also voted in favour of publishing our objection. The US researchers released a statement thanking us for our work and have since endorsed our arguments. They now also assume that it can’t have been a comet.

What have you taken away from the process and what can the science community and the general public learn from it?

This shows how important it is to discuss scientific findings and call upon the expertise of different scientists who were not involved in the original research. However, it is regrettable that certain narratives attract different levels of public attention. The news of the supposed comet garnered a great deal of media coverage in the USA with reports from newspapers such as the »Washington Post«. This may have been supported by recent movies such as »Greenland« and »Don’t Look Up«, in which comets enter the Earth’s atmosphere and explode or hit the surface. By contrast, our correction has not enjoyed anywhere near as much publicity, even though we have seen very positive responses, especially in geophysical circles. However, an air burst from an asteroid or bolide is much more realistic and, depending on its size, can even be more devastating – we only have to look at the extinction of the dinosaurs 66 million years ago or the sheer devastation and injuries caused by the much smaller Tunguska event in 1908 or the Chelyabinsk meteor in 2013.