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Title: Resolve the conflict between solar abundances and helioseismology
Plain: Measurements of the Sun's surface composition give less carbon, oxygen and other heavy elements than the Sun's internal sound waves imply.
Precise: Standard solar models using 3D non-LTE photospheric abundances (Asplund et al. 2009 and 2021, $Z/X \sim 0.018$) disagree with the helioseismic sound speed below the convection zone (deviations $\sim 1\,\text{percent}$), the convection-zone base $R_{\mathrm{cz}} = 0.713\,R_{\mathrm{sun}}$ and surface helium $Y_{s} \sim 0.248$, while higher-metallicity analyses (Magg et al. 2022, $Z/X = 0.0225$) restore much of the agreement. Determine the correct metal content and whether opacity revisions near $T \sim 2e6\,\mathrm{K}$ or other physics are needed. Answer: $Z/X$ with uncertainty consistent with helioseismology and the CNO solar neutrino flux.
Settled by: A precise CNO neutrino flux measurement (fixing core C+N) together with laboratory opacity measurements at solar interior conditions.
Kind: well-posed
Answer type: value
References: (empty)
Literature status: contested
Status note: Borexino CNO neutrino fluxes (2020-2022) mildly favor the higher-metallicity composition; helioseismic opacity inversions suggest opacities above current tables near the convection-zone base.
Posed since: 2005