Study Identifies Hidden Force Deep Inside Earth That May Affect Day Length

Study Identifies Hidden Force Deep Inside Earth That May Affect Day Length
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Two physicists at Canada’s University of Alberta have identified a hidden force deep inside Earth that may slightly alter the planet’s rotation, changing the length of a day by fractions of a millisecond.

Researchers Huifeng Zhang and Matthew Dumberry analyzed seismic records from 1964 to 2019, combining observations of the inner core’s rotation with models of the movement of the liquid outer core. They also accounted for other factors, including winds, oceans and the Moon’s long-term influence.

The findings suggest that gravitational interaction between the inner core and surrounding mantle provides the most consistent explanation for the observed changes in day length.

The inner core, composed mainly of iron and nickel, is not perfectly spherical, while the mantle has an uneven mass distribution. As these differences interact during the core’s rotation, they can generate a gravitational torque capable of slightly speeding up or slowing Earth’s rotation.

The researchers linked the phenomenon to a pattern of changes spanning roughly 70 years. Their models also suggest that the solid inner core can gradually change shape in response to surrounding forces, with such changes potentially occurring over periods of eight to 10 years.

The study also found indirect evidence of a roughly two-kilometer-thick, electrically conductive, iron-rich layer near the base of the mantle.

However, the researchers cautioned against treating the 70-year pattern as a fixed cycle, noting uncertainties in the models. They said tiny variations in day length could provide valuable clues about the movement and composition of materials deep inside Earth.