Gravitational Torque Drives Earth's Length of Day Fluctuations

Gravitational torque has been identified as the primary driver of multidecadal fluctuations in Earth's length of day, according to research published online on September 23, 2026, in the journal Nature. This finding significantly enhances the scientific community's understanding of the complex material properties and dynamic processes occurring within Earth's deep interior. The study posits that while gravitational torque initiates these variations, they are subsequently counteracted by resistive forces, specifically electromagnetic and topographic influences. These resistive forces play a crucial role in modulating the magnitude and duration of the length-of-day changes.

The research, detailed in the article "Gravitational torque drives multidecadal variations in length of day" with the DOI 10.1038/s41586-026-10999-2, provides a new framework for interpreting observed changes in Earth's rotation. Previously, scientists have observed irregular variations in the length of the day, which refers to the time it takes for the Earth to complete one full rotation on its axis. These variations can be influenced by a multitude of factors, including atmospheric and oceanic currents, the movement of molten iron in the Earth's core, and the melting and refreezing of ice sheets. However, the specific contribution of gravitational torque to longer-term, multidecadal cycles had not been as clearly delineated.

This new study leverages advanced geophysical modeling and observational data to isolate the effect of gravitational torque. Gravitational torque arises from the differential gravitational pull of celestial bodies, such as the Moon and the Sun, on different parts of the Earth. These tidal forces can exert a torque on the solid Earth, influencing its rotation rate. The research quantifies the magnitude of this torque and demonstrates its correlation with observed multidecadal patterns in the length of day. The findings suggest that these gravitational influences are a more dominant factor in long-term rotational variability than previously appreciated.

Furthermore, the study highlights the importance of electromagnetic and topographic forces as counteracting mechanisms. Electromagnetic forces are generated by the interaction of Earth's magnetic field with conductive materials within the planet, particularly in the liquid outer core. Topographic forces are related to the irregular shape of the Earth's surface and its internal density variations. The interplay between the driving gravitational torque and these resisting forces creates a complex system that dictates the precise rate of Earth's rotation over decadal timescales. This improved understanding could have implications for fields ranging from geodesy and geophysics to climate modeling and satellite navigation, which rely on precise knowledge of Earth's rotational parameters.