A study indicates that the inner core of the Earth is currently changing the direction of its rotation

Publication published in the journal nature It indicates that the metallic sphere in the core of our planet is subject to a conflict between the Earth’s magnetic field and its mantle.

imagine. Lying 5,000 kilometers below our feet, a ball with a diameter of 2,446 kilometers rotates on itself, floating in a metallic soup. This is the inner core of our planet, consisting of an alloy of iron and nickel heated to more than 5,500 degrees Celsius. Discovered by the Danish seismologist Inge Lehmann in 1936, it never ceases to amaze scientists.

“It is unbelievable that there is a solid metal ball floating in the middle of the earth,” she exclaims again with The New York Times John Vidal, a seismologist at the University of Southern California.

Especially since she’s not done revealing all her secrets to us. In a study published Monday in the journal Natural Earth SciencesSeismologists from Peking University Yi Yang and Xiaodong Song suggest that our planet’s “seed” responds to a 70-year cycle. Every 35 years, it will change direction of rotation. We will go through one of these changes.

Rotation was discontinued between 2009 and 2011

To reach their conclusions, the two scientists studied seismic waves recorded from the 1960s to the present day, caused by earthquakes and nuclear tests. For although it is impossible to study the inner core, which is very deep, directly, the waves that reach it are not.

However, if the inert and contained inner core follows the direction of Earth’s rotation, the seismic waves that scientists measure will always take the same path. But over time, this “path” is changing. At the end of the 20th century, Professor Xiaodong Song had already suggested that this metal ball was moving at a speed different from that of our planet.

This Monday, along with colleague Yi Yang, presents a more detailed scenario. In 1970, “The Seed” remained a constant. Then it began to gradually turn towards the east, before exceeding the direction of the Earth’s rotation, then slowed down, to finally stop between 2009 and 2011. Since then, it has resumed its rotation, but this time towards the west. You must set a new station in the year 2040, before heading back east.

A fluctuation every seven decades?

To reach these conclusions, Chinese scientists first analyzed seismic waves that occurred since the early 1990s, and showed little change in trajectory over the past decade.

“This globally consistent pattern indicates that the inner core’s rotation has recently stalled,” they explained in their study.

“We compared this recent pattern to seismic records from the South Sandwich Islands dating back to 1964 and it appears to be related to the gradual return of the inner core as part of a roughly seven-decade oscillation, with another turning point in the early 1960s. 1970s,” they detail.

“We only have 57 years of data, so it needs to be taken into account. (…) When we have another 50 years of data, we will have more perspective to believe in this value. In any case, this seems to show a very long trend, “details Parisian Severine Rosat is a geophysicist at the University of Strasbourg.

Arm wrestling under our feet

To explain this possible change in rotation, the two worlds evoke the confrontation taking place under our feet for control of the inner core. As noted before The New York TimesYi Yang and Xiaodong Song believe that the Earth’s magnetic field rotates the inner core in one direction. But this thrust is offset by the Earth’s mantle and massive gravitational field, which slow the rotation of the metallic sphere that is the inner core.

Does this fierce fighting beneath our feet have an effect on the surface? Chinese seismologists believe that if this is the case, the consequences will be minor. The changement of rotation of noyau interne pourrait venir modifier légèrement le champ magnétique of notre planet, débouchant sur une très légère alteration de la durée d’une journée, dont on sait qu’elle augmente et diminue d’une fraction de milliseconde tous les six years.

Will we ever know for sure what is happening under our feet? I’m not sure, says Professor Vidale who interviewed him The New York Times, reinforcing the current technical impossibility of accessing this underground haven. “It’s very likely we’ll never find out the truth,” he says. “(…) But I’m an optimist. One day the pieces will come together.”