Scientists from the University of Southern California (USC) have confirmed that the Earth’s inner core is rotating more slowly than the planet’s surface. This groundbreaking research poses significant questions about planetary mechanics and could profoundly impact both Earth’s magnetic field stability and the length of our days, according to a report from Science Alert.

Published in Nature, the study presents evidence that since around 2010, the inner core has been slowing down, marking the first time in about 40 years that it is moving slower than the Earth’s mantle. Notably, the inner core—a dense, super-hot sphere composed of iron and nickel—is situated more than 4,800 kilometers beneath the Earth’s surface.

John Vidale and his colleagues conducted the study by analyzing data from 121 repeating earthquakes recorded between 1991 and 2023 near the South Sandwich Islands in the South Atlantic. They also utilized data from Soviet nuclear tests conducted from 1971 to 1974, as well as from French and American nuclear tests from other research on the inner core.

“When I first observed the seismograms suggesting this change, I was puzzled. However, after discovering two dozen more observations indicating the same trend, the conclusion was unavoidable. The inner core has slowed down for the first time in many decades. Other scientists have recently proposed various models, but our latest study offers the most convincing explanation,” said Mr. Vidale, Dean’s Professor of Earth Sciences at the USC Dornsife College of Letters, Arts and Sciences.

Mr. Vidale explained that the slowdown in the inner core’s rotation is influenced by the turbulent movement of the surrounding liquid outer core, which generates Earth’s magnetic field, as well as gravitational forces from dense regions in the rocky mantle above.

This phenomenon could potentially alter the entire planet’s rotation, leading to longer days. Mr. Vidale noted that the adjustment in the inner core’s movement might change the length of a day by fractions of a second: “It’s very subtle, on the order of a thousandth of a second, almost imperceptible amidst the disturbances caused by the oceans and atmosphere.”

The team now aims to map the inner core’s trajectory in even greater detail to uncover precisely why it is undergoing these changes. “The dynamics of the inner core’s movement might be even more complex than what we currently understand,” Mr. Vidale remarked.