5,000 km below our feet, Earth’s core could just start rotating upside down, according to a new study – Liberation

Deep below Earth’s surface, the giants may begin to turn the other way from us, according to a study whose conclusions should not put an end to the controversy plaguing specialists on this matter. Earth’s core, a burning ball about the size of Pluto, has stopped rotating and may even have gone the other way, said the study published Monday in the journal Natural Geosciences. This “planet within a planet” is essentially made of iron, some 5,000 km below the surface, free to move as it floats in the molten outer core.

The exact mechanism of this rotation, however, remains a matter of deep debate. Because what little we know is based on a subtle analysis of seismic waves caused by earthquakes as they pass through the center of the planet. Analyzing seismic wave data for the past sixty years, Xiaodong Song and Yi Yang of Peking University concluded that the core rotates “nearly stopped around 2009 before going back the other way”.

“We believe that the central core, relative to the Earth’s surface, rotates one way and then the other, like a seesaw.”they say. “Complete cycle [dans un sens puis dans l’autre] this swing is about seventy years old”, According to them. The last rotation change before 2009 would have occurred in the early 1970s, the next would occur in the mid-2040s, completing the cycle, according to Chinese researchers.

According to them, this rotation would be more or less related to changes in the length of the day, small variations in the exact time it takes the Earth to rotate on its axis. Until now, indications of the influence of this rotation on what is happening on the surface of the earth are still few. But both authors believe that there is a physical connection between all the layers that make up the Earth. “We hope our research motivates researchers to design and test models that treat Earth as an integrated dynamic system.”they explained.

Nevertheless, independent experts are welcoming the research with great interest but also with some caution. “This is a very careful study done by great scientists that uses a lot of data,” said John Vidale, a seismologist at the University of Southern California. But according to him, “none of the existing models explain all the available data very well”.

John Vidale published a study last year showing that the inner core is oscillating much more rapidly, changing direction every six years, according to seismic data from two nuclear explosions that occurred in the late 1960s and early 1960s. demonstrated by studies of Chinese researchers, “as it happens”according to American seismologists.

“Russian doll”

Another theory, with solid foundations according to John Vidale: the inner core only moved significantly between 2001 and 2013, before stabilizing since then. For Hrvoje Tkalcic, a geophysicist at the Australian National University, the inner core cycle is about twenty to thirty years, not the seventy years suggested by research at Natural Geosciences. “This mathematical model may be all wrong” because even if they explain the observed data, the latter may respond to other, as yet unimaginable, models, he added.

Therefore, according to him, the geophysical community has many reasons for this “divided over the discovery, and the topic remains controversial”. He compared seismologists to doctors “who studies the internal organs of patients with imperfect or limited equipment”. It’s as if we are trying to understand the function of the liver only with the help of ultrasound.

Without the equivalent of a scanner, “our representation of Earth’s interior is still unclear”, regretted Hrvoje Tkalcic, expecting another surprise in this area. Such is the theory that the inner core hides a smaller iron ball, modeled after a Russian doll.