Physicists Identify Cause of Earths Rotation Fluctuations

A new study reveals gravitational torque between the inner core and mantle drives fluctuations in the length of a day.

Updated on Oct. 25, 2026 in Geology

A detailed cross-section model showing Earth's core rocking within its mantle, depicted as a physical metallic and geological specimen. — University of Alberta researchers identified gravitational torque between the inner core and mantle as the primary cause of Earth's rotational fluctuations. AI Illustration. Upload story photo >

University of Alberta researchers published a study on September 23, 2026, identifying gravitational torque as the source of Earths day-length fluctuations. The team linked these changes to the solid inner core rocking back and forth against the mantle.

Why it matters

Understanding the interplay between the inner core and the mantle provides essential insight into how Earths angular momentum remains constant. The findings help clarify the complex relationship between internal planetary movements and surface timekeeping.

The study utilized seismic data to track the inner core, which oscillates 2.35 degrees against a mantle that is approximately 1,860 miles thick. Researchers also inferred the existence of an iron-rich layer 1.2 miles thick at the base of the mantle.

The players

Huifeng Zhang

He is a physicist at the University of Alberta who co-authored the research comparing long-term rotation data to inner core movement.

Mathieu Dumberry

He is a University of Alberta physicist who contributed to the study on gravitational torque between the Earths core and mantle.

The details

Flows within the liquid outer core utilize magnetic forces to pull the inner core out of alignment, creating a gravitational torque that twists the mantle. This interaction forces the inner core to rock against the mantle, a movement that researchers determined changed direction around 2010.

1964-2019: Data range for rotation and core motion comparison.
2010: The year the inner core changed its direction of motion.
2023: Inner core reconstruction published by Yang and Song.
September 23, 2026: Study published in Nature.

The Big Picture

This research aligns with the findings published in Nature, extending our understanding of how the core-mantle boundary influences global rotation metrics. It updates figures previously established by seismic reconstructions and clarifies the complex physics of planetary angular momentum.

While these geophysical findings do not change daily life, the improved understanding of Earths core dynamics assists scientists in refining global timekeeping models. Such research is critical for ensuring the accuracy of modern satellite navigation and communication systems.

The takeaway

These findings underscore that Earths rotation is an evolving system influenced by deep-seated internal forces rather than a perfectly constant spin. The study confirms that even the deepest layers of the planet have measurable effects on the surface environment over multi-year cycles.