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Accepted · first revision · record

Title: Are the deep mantle slow regions denser or lighter than their surroundings?
Plain: If the two big regions are denser than normal mantle they are chemically different and long-lived; if lighter they are probably just hot. Different methods give opposite answers.
Precise: Determine the sign and magnitude of the density anomaly $\delta \rho/\rho$ in the lowermost 300 to 500 km of the LLSVPs. Normal-mode and Stoneley-mode inversions have favored lighter material while body-tide tomography (Lau and coauthors, Nature 2017) favored denser material. An answer is $\delta \rho/\rho$ with uncertainty below about 0.3 percent from mutually consistent methods.
Settled by: Combined normal-mode, body-tide and satellite-gravity inversions with shared parametrization and resolution tests.
Kind: well-posed
Answer type: value
References: (empty)
Literature status: contested
Status note: A 2026 satellite-gravity analysis (arXiv:2606.09296) adds new constraints; methods still disagree.
Posed since: (empty)