Satellite Gravity Data Reveals New Constraints on Earth's Inner Core Viscosity and Deep Mantle Structure
Researchers have used satellite gravity observations to constrain the viscosity of Earth's solid inner core to approximately 4.6 × 10¹⁶ Pascal-seconds and identified density anomalies in large low-velocity provinces (LLVPs) at the base of the mantle. The study developed a unified dynamical framework linking mantle-inner core gravitational coupling with fluid outer core oscillations, detecting a robust ~6-year periodic signal in satellite gravity data that also appears in length-of-day variations. The findings suggest satellite gravimetry can serve as a direct observational tool for probing deep-Earth physical properties that have historically been very difficult to constrain.
A new preprint posted to arXiv presents a geophysical framework that connects mantle-inner core gravitational coupling (MICG) with torsional oscillations in the fluid outer core, predicting a geodetic signature detectable from space. Analyzing satellite gravity data (Stokes coefficient ΔS₂₂) alongside corrections for surface mass variability, the authors identified a statistically robust approximately 6-year periodic signal, while no corresponding stationary signal was found in ΔC₂₂. The same ~6-year periodicity was independently detected in length-of-day (ΔLOD) variations, and the two signals display a near anti-phase relationship, lending credibility to the proposed coupling mechanism. Inverting these observations within the framework, the team estimates inner core viscosity at 4.6 (±1.8) × 10¹⁶ Pa·s and an equatorial inner core boundary relief with a semi-axis difference of roughly 200 ± 70 meters. Additionally, the inversion yields mean density anomalies of +5.5 (±0.6) per mil at the base of LLVPs — the large low-velocity provinces in the deep mantle whose nature remains debated. The study, spanning 53 pages and 14 figures, argues that satellite gravimetry opens a new observational window into deep-Earth dynamics previously accessible only through seismology and numerical modeling.
What's missing
As a preprint, this work has not yet undergone formal peer review, so the methodology and error estimates have not been independently validated. The study's own key limitations include the relatively large uncertainty on the viscosity estimate (±1.8 × 10¹⁶ Pa·s, roughly 40% of the central value), the assumption of specific coupling mechanisms whose relative contributions may not be fully separable, and the challenge of isolating the deep-Earth signal from surface and atmospheric mass variability corrections. The physical interpretation of LLVPs — whether they are thermochemical piles, subducted slabs, or primordial reservoirs — is not resolved by this study, and the density anomaly estimate depends on model assumptions about their geometry.
What different sources said
- arXiv physicsCenter
Satellite gravity constraints on inner core viscosity and LLVPs density anomalies
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