Recent research has revealed that the rotation of the Earth’s inner core is not in sync with the rotation of the mantle, creating a wobble that has measurable effects on our planet. The inner core, a ball of mostly iron and nickel, is 2,440 kilometers (1,520 miles) across, and it sits at the very center of the Earth. Surrounding the inner core is the outer core, made of molten liquid metal and 2,260 kilometers (1,400 miles) thick, which is the main source of the planet’s magnetic field.
The new study suggests that the rotation axis of the inner core is 0.17 degrees off compared to the rotation of the mantle, a much smaller value than the previous assumption of 10 degrees used in some geodynamical models.
The tilt between the mantle and the core is currently static and pointing west, indicating that the northwestern hemisphere of the inner core might be slightly more dense than the rest. The discovery of this misalignment is helping to explain the small variations in the day length and polar motion of the Earth.
Since the late 1980s, researchers have suspected that a coupling between the inner core and the mantle could be responsible for a periodic variation on the order of 10 years. This study puts the wobble at 8.5 years, plus or minus 75 days, and the discovery of a signal in the polar motion back in 2018, combined with the day-length fluctuations, led the researchers to conclude that they were being caused by the same process.
The wobble and the misalignment also imply that the outer core and inner core not only differ in state (one solid and one liquid) but also in density.
The implications of this research are significant in our understanding of the Earth’s inner workings, and the study has been published in Nature Communications. This new insight into the inner core will help scientists further understand the complex dynamics of the Earth’s interior and how it influences the planet’s overall behavior.