What does the magnetic field of the much smaller Mercury suggest about the critical factor causing Venus's dynamo failure?

Answer

Venus's extreme slow rotation is the disqualifying factor for its dynamo.

Since Mercury, which is smaller and likely cooled faster, still sustains a weak global field, this strongly points to Venus's rotational speed being the critical kinematic requirement preventing its dynamo from establishing a global field.

What does the magnetic field of the much smaller Mercury suggest about the critical factor causing Venus's dynamo failure?
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