Researchers have proposed that gravitational forces between Earth's inner core and mantle contribute to long-term variations in the length of days.

Scientists have identified a gravitational mechanism within Earth's interior that influences the planet's rotation speed. A study published in Nature suggests that the inner core's misalignment with the mantle creates a competitive gravitational pull, resulting in minute accelerations and decelerations of the planet's spin over decades.

The Role of Earth's Interior

While factors like atmospheric fluctuations, ocean currents, and earthquakes cause short-term changes in rotation, researchers have long sought the source of variations occurring over several decades. The study focuses on the outer core, a 1,400-mile-thick layer of liquid metal, and its interaction with the inner core. Because friction between the core and mantle is insufficient to explain these shifts, the team investigated gravitational forces as a primary driver.

Gravitational Tug-of-War

The research team, including geophysicist Mathieu Dumberry of the University of Alberta, posits that the inner core rotates at a different rate than the rest of the planet, leading to a misalignment with mass irregularities in the mantle. Gravity acts to pull these layers back into a harmonic position. The authors validated this model by reconstructing Earth's spin data from 1964 to 2019, finding that their gravitational model accurately reflected the timing and magnitude of observed historical changes.