Lhe controversy has long stirred specialists in the field… Far below the earth’s surface, a giant may have started to turn away from us! Earth’s core, a burning sphere the size of Pluto, has stopped rotating and may even have gone in the opposite direction, according to a study published Monday (January 23) in Geoscience of nature.
This “planet within a planet” made essentially of iron, about 5,000 km below the surface, is free to move, because it floats in the liquid envelope of the outer core. The exact mechanism of this rotation remains a matter of debate, because what little we know about it is based on the detailed analysis of seismic waves, caused by earthquakes, as they pass through the center of the planet.
Analyzing seismic wave data from the past six decades, Xiaodong Song and Yi Yang of Peking University concluded that the rotation of the core “almost stopped around 2009 before starting again in the opposite direction.” “We believe that the central core is, relative to the surface of the earth, rotating in one direction and then another, like a seesaw,” they told Agence France-Presse (AFP).
“A full cycle (back and forth) of this swing is about seventy years,” they say. The last rotation change before that of 2009 would have occurred in the early 70s. The next would have occurred in the mid-2040s, completing the cycle, according to Chinese researchers.
A “very careful study”
According to them, this rotation would be more or less linked to changes in the length of the day, small variations in the exact time the Earth needs to rotate on its axis.
To date, there is little indication of an influence of this rotation on what happens on the earth’s surface. But the two authors are convinced that there are physical links between all the layers that make up the Earth. “We hope our research will motivate researchers to design and test models that treat the Earth as an integrated dynamic system,” they explain.
Independent experts have welcomed this research with interest but also with some reservations. “This is a very careful study by excellent scientists using a lot of data,” John Vidale, a seismologist at the University of Southern California, told AFP. But according to him, “none of the existing models explains all the available data very well.”
John Vidale published a study last year suggesting that the inner core is swinging much faster, changing direction about every six years, according to seismic data from two nuclear blasts dating back to the late 1960s and early 1960s. 60. the one indicated by the study of Chinese researchers, “a coincidence”, according to the American seismologist.
Another theory, with solid foundations according to John Vidale: The inner core only moved significantly between 2001 and 2013, before leveling off since then.
For Hrvoje Tkalcic, a geophysicist at the Australian National University, the cycle of the inner core is about 20-30 years, instead of the 70 years suggested by the study in Geoscience of nature. “Probably these mathematical models are all wrong” because even if they explain the observed data, the latter could respond to other models yet to be imagined, he says.
The geophysics community therefore has, according to him, every reason to be “divided over this discovery, and the topic to remain controversial”.
He likens seismologists to physicians “who study a patient’s internal organs with imperfect or limited equipment.” As if we were trying to understand the functioning of the liver only with the help of an ultrasound. Without the equivalent of a scanner, “our representation of the Earth’s interior remains fuzzy,” he says, expecting more surprises in this area.
Like the theory that the inner core contains an even smaller iron sphere, modeled after Russian dolls.