&gt;  Assuming the mass of the planet remains constant, wouldn&#x27;t you get 4 times the gravitational force at the surface?<p>No idea why you&#x27;d ask this question but yes.<p>But the original statement is wrong isn&#x27;t it, if you half the diameter you 1&#x2F;8 the gravity [1&#x2F;8 the mass]<p>[edit] But you&#x27;d also be twice closer, which is 4 times the force, got it.