The length of a day on Earth only appears constant: in reality, the planet's rotation speed fluctuates slightly, making days sometimes a little longer and sometimes a little shorter. According to ScienceDaily, changes in the rotation speed of Earth's interior affect the length of the day, shifting it by several milliseconds every few decades, infohub.kz reports.
Scientists have long noted that the planet's liquid core alternately speeds up and slows down. The mantle — a rocky shell about 3,000 kilometers thick — responds in the opposite way, preserving the planet's total angular momentum.
In a new study, physicists at the University of Alberta explained the mechanism behind this interaction. Changes in the rotation speed of the solid inner core create a gravitational torque. Because the inner core is not perfectly round, its motion exerts a gravitational pull on the mantle's uneven mass distribution, nudging it forward or slowing it down.
This force is counteracted by friction and electromagnetic resistance at the boundary between the core and the mantle. It is the balance of these processes that determines how much the length of the day changes. In addition, the authors found that the inner core can change shape under stress, responding to external forces far more dynamically than previously thought.