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Title: How does Ganymede sustain a core dynamo today?
Plain: Jupiter's moon Ganymede is the only moon known to make its own magnetic field. Models of how such a small body cools suggest its core should have stopped stirring long ago.
Precise: Galileo detected an intrinsic dipole with surface equatorial strength near 7e-3 G. Identify the power source that keeps Ganymede's Fe-FeS core convecting after 4.5 Gyr: iron snow, FeS crystallization, compositional convection, or heat from past tidal heating during resonance passage. An answer is a thermal-chemical evolution model producing a present dynamo of the observed strength.
Settled by: JUICE orbital measurements of field harmonics, induction response and gravity (Love numbers) constraining core size and state.
Kind: phenomenon
Answer type: mechanism
References: (empty)
Literature status: open
Status note: JUICE is planned to arrive at Jupiter in 2031 and orbit Ganymede from 2034.
Posed since: 1996