Why does Mercury have such an outsized iron core?
In plain words
About 70 percent of Mercury's mass is in its metal core, far more than for Earth or Mars. It may have lost its rocky outer layers in a giant impact, or formed from material enriched in iron near the Sun.
Precise statement
Explain Mercury's metal mass fraction (about 0.7) by mantle stripping in one or more hit-and-run or giant impacts, by chemical or magnetic sorting of iron-bearing solids in the inner disk, or by evaporation, consistent with MESSENGER's detection of a surface high in volatile elements (high K/Th, S, Na). An answer is a scenario matching bulk composition and volatile inventory.
What would settle it
BepiColombo measurements of Mercury's interior and surface composition combined with formation models that predict both the metal fraction and the volatile abundances.
Status in the literature
Unverified note
BepiColombo is scheduled to enter Mercury orbit in late November 2026, with interior and surface-composition measurements to follow.