Inner core shifts may explain millisecond changes in Earth's day length
Researchers propose that subtle movements of Earth's solid inner core generate a gravitational torque that alters mantle rotation, causing the planet's day to vary by a few milliseconds over decades.
For decades scientists have known that Earth's rotation is not perfectly constant, with day length changing by milliseconds. New research attributes these variations to a gravitational torque produced when the solid inner core, which is not perfectly spherical, shifts its rotation. The torque interacts with mass irregularities in the mantle, causing the mantle to speed up or slow down in opposition to the liquid outer core.
This exchange is countered by core-mantle boundary torque, which provides frictional and electromagnetic resistance, limiting the magnitude of day-length changes. The authors also report that the inner core appears to deform viscously over about a ten-year period, suggesting a surprisingly active deep interior. These insights help resolve a longstanding mystery about Earth's rotational dynamics.
