The speed at which Earth’s inner core rotates is not fixed; it rises and falls over time. Findings reported through the University of Southern California’s press service via TASS indicate a clear pattern of variability in the rotation rate that defies a single, steady pace.
Researchers describe a measurable difference between the rotation of the planet’s crust and the inner core. The data show that the rates do not match exactly and that this difference itself varies in a periodic way. In years around 1969 to 1971 the inner core lagged behind the surface, while in 1971 to 1974 it appeared to move faster than the outer layers. These observations point to repeating fluctuations in how quickly the inner core turns compared with the rest of the planet.
The period under discussion relied on a global sequence of nuclear tests conducted during 1969 to 1974 in separate locations, including underground sites on Novaya Zemlya and the Amchitka Island in the United States. Seismic signals produced by these underground explosions were continuously monitored by the American seismic network, including LASA stations in Montana. As seismic waves traveled through the planet, some reflected off the inner core and returned to the surface. Scientists used these reflections to infer how the central region’s rotation compared with the surface. By analyzing the timing and strength of the echoes, researchers concluded that the inner core’s rotation was indeed slower than the surface during 1969 to 1971 and faster during 1971 to 1974.
Despite the clarity of these measurements, the mechanism driving the observed oscillations remains uncertain. Scientists propose that the fluctuations could be tied to complex dynamics within Earth’s interior, including interactions between the inner core and the liquid outer core, anisotropic properties of materials at extreme pressures, and variable momentum exchange across boundary layers. The idea that the length of a day can shift by as much as roughly 0.2 seconds over a six-year cycle follows from these seismic insights and highlights how deeply the planet’s internal processes can influence surface timekeeping. Ongoing and improved seismic monitoring is essential to constrain the possible causes of these oscillations and to determine whether the pattern is part of a longer, perhaps multi-decadal, cycle.
In a different line of astronomical observation, progress in high-energy astrophysics continues to reveal the behavior of compact objects. The Hubble Space Telescope has contributed to breakthroughs in identifying and characterizing black holes, including efforts to estimate their masses and locate them within galaxies. These discoveries, while not directly connected to Earth’s interior dynamics, underscore the broader scientific interest in how extreme gravitational environments govern the behavior of matter and space-time, reinforcing the value of precise measurement and long-baseline observational campaigns.