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Title: How did the Moon's small core make a strong ancient field?
Plain: Some old Moon rocks record a magnetic field about as strong as Earth's, though the Moon's iron core is tiny. Either an unusual power source existed or the measurements are misleading.
Precise: Apollo sample paleointensities suggest surface fields of roughly 0.2 to 1 G between about 4.0 and 3.5 Ga, difficult to power by thermal convection in a core of radius near 350 km. Determine whether these records reflect a core dynamo (driven by precession, mantle stirring by impacts, or a basal magma ocean), impact-generated transient fields, or overestimated paleointensities. An answer is a reconciled paleointensity record with a physically allowed source.
Settled by: Paleointensity measurements on well-dated, unshocked lunar samples, including new returned samples, with energy-budget tests of candidate dynamos.
Kind: well-posed
Answer type: identification
References: (empty)
Literature status: contested
Status note: Narrett and coauthors 2025 (Science Advances, https://doi.org/10.1126/sciadv.adr7401) show that basin-forming impact plasmas could amplify a weak dynamo field of about 0.02 G to about 0.4 G near the basin antipode, which may explain the strong paleointensities without a strong dynamo; contested.
Posed since: (empty)