Fact #057
Geology
The Moon has a core, and part of it is still molten. It is tiny: about a fifth of the Moon's radius, against half for Earth's.
Reanalysis of Apollo seismic data in 2011 found a solid inner core and a fluid outer one, with a partly melted boundary layer above. That small core is a big reason the Moon's dynamo shut down: not enough churning metal to keep a magnetic field running.
Source: Apollo seismic reanalysis, NASA (opens in a new tab) · checked Aug 2026