Gravitational Tug-of-War in Earth's Core Alters Day Length
New study reveals how inner core dynamics subtly change Earth's rotation speed.
1Millisecond variations in day length
Earth's rotation speed fluctuates by milliseconds due to atmospheric changes, ocean currents, and ice melt. These tiny variations accumulate over decades, revealing deeper planetary dynamics. Scientists track these changes to understand Earth's internal mechanisms. The variations are imperceptible but crucial for long-term geophysical models.
2Outer core's liquid metal dynamics
A 1,400-mile-thick layer of molten metal in Earth's outer core constantly shifts, influencing rotation speed. These flows create subtle torque effects on the mantle above. Unlike sudden changes from earthquakes, core movements cause gradual decadal variations. The exact transmission mechanism remained unknown until recent research.
3Inner core-mantle gravitational battle
New Nature study identifies misalignment between inner core and mantle irregularities as key. Gravity pulls the inner core toward alignment, creating opposing rotational forces. This tug-of-war between core layers affects surface rotation speed. Researchers modeled this using 55 years of seismic data and fluid dynamics.
4Decadal-scale rotational changes explained
The gravitational model accurately reproduced observed day-length variations from 1964-2019. It accounts for about 70% of measured changes in Earth's rotation speed. The remaining 30% suggests other undiscovered mechanisms at work. This represents the first quantitative link between core dynamics and surface rotation.
5Seismic data meets fluid dynamics
Researchers combined inner core rotation estimates with outer core flow models. This dual approach allowed tracking gravitational interactions between layers. The team verified predictions against actual rotational measurements. Their work provides a framework for future core-mantle interaction studies.
6Persistent gravitational dominance
Despite competing forces, gravity ultimately determines the core-mantle alignment. This creates a net effect on planetary rotation over decades. The study confirms gravity as the primary driver of long-term rotational variations. Other factors like earthquakes cause shorter-term disturbances.
7Implications for Earth system science
The findings improve understanding of planetary angular momentum transfer. They help explain historical changes in day length recorded since 1960s. The model aids prediction of future rotational variations. This advances geophysical models of Earth's deep interior dynamics.
8Unanswered questions remain
About 30% of rotational changes still lack explanation. Researchers suspect additional core-mantle interactions may be involved. Future studies will explore electromagnetic coupling effects. The work opens new avenues for investigating Earth's deepest layers.
Original article: Science Latest — Gravitational Tug-of-War in Earth's Core Alters Day Length