{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"0a84a25e1e00358edb3d50413b88154dd358ce4c34c336dc2c415e5bf6cfb5ff","created":"2026-10-03T07:18:03Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"5083be645935d834ce728c6b8202a66636803b35fdb7816a3b871a7ef1ea6d0b","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"identification","assisted_by":[],"external_id":"earth.planetary-dynamos.lunar-dynamo","kind":"well-posed","literature_status":"contested","n":"1","parents":[],"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.","posed_since":"","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.","problem_ref":null,"references":"","settled_by":"Paleointensity measurements on well-dated, unshocked lunar samples, including new returned samples, with energy-budget tests of candidate dynamos.","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.","title":"How did the Moon's small core make a strong ancient 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