Earth’s day isn’t exactly 24 hours. The reason may lie deep inside the planet
Physicists have identified that gravitational torque caused by the Earth's inner core interacting with the mantle influences the planet's rotation. This interaction explains the subtle, millisecond-level fluctuations in the length of a day.
Why it matters
Understanding these internal planetary dynamics is crucial for precise timekeeping and improving our fundamental knowledge of Earth's geophysical processes.
Most of us think of a day as a fixed 24 hours. In reality, Earth's rotation is not perfectly constant.
The difference is tiny, measured in milliseconds, but physicists can detect it. Over time, some days become slightly shorter or longer depending on subtle changes deep inside the planet.
For roughly three decades, scientists have known that Earth's liquid core does not always rotate at the same rate. Changes in the planet's magnetic field have revealed that the liquid core can gradually speed up over several decades, then slow down during the following decades.
At the same time, the mantle, the roughly 3,000 kilometer thick rocky layer that includes the crust, responds in the opposite direction. When the core speeds up, the mantle slows slightly. When the core slows, the mantle speeds up.
This exchange happens because Earth's total angular momentum must remain constant.
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