Satellite Gravity Data Reveals New Constraints on Earth's Inner Core Viscosity and Deep Mantle Structure
Researchers used satellite gravity observations combined with length-of-day measurements to constrain the viscosity of Earth's solid inner core and the density structure of large low-velocity provinces in the deep mantle. The study identified a robust 6-year periodic signal in gravitational data that, when interpreted through a new dynamical framework linking inner core and outer core processes, yields estimates of inner core viscosity and mantle density anomalies. These findings demonstrate that satellite gravimetry can provide direct observational constraints on Earth's deep interior, which is crucial for understanding planetary dynamics and internal structure.
A new study published on arXiv develops a unified dynamical framework combining mantle-inner core gravitational coupling with torsional oscillations in Earth's fluid outer core to predict detectable geodetic signatures. The researchers analyzed satellite gravity observations from the Gravity Recovery and Climate Experiment (GRACE) and related missions, along with independent corrections for surface mass variability, and identified a statistically robust approximately 6-year periodic signal in the Stokes coefficient Delta S22. This signal was independently corroborated by length-of-day variations measured through other geophysical techniques, with the two signals exhibiting a near anti-phase relationship. Using this coupled signature within their proposed framework, the authors constrain the inner core viscosity to approximately 4.6 (±1.8) × 10^16 Pa·s and estimate the equatorial relief of the inner core boundary at about 200 ± 70 meters. The inversion analysis further indicates mean density anomalies of +5.5 (±0.6) per mil at the base of large low-velocity provinces, suggesting that satellite gravimetry provides a direct observational window into deep-Earth dynamics.
What's missing
The study's own limitations include: the interpretation relies on a specific dynamical framework that would benefit from independent validation through other geophysical methods (seismology, mineral physics); the 6-year signal's physical origin and whether it represents steady-state or transient dynamics requires further investigation; and the density anomalies inferred for LLVPs depend on assumptions about their lateral extent and composition, which remain uncertain from seismic data alone.
What different sources said
- arXiv physicsCenter
Satellite gravity constraints on inner core viscosity and LLVPs density anomalies
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