Answer:
Drop by a factor of 64
Step-by-step explanation:
By Newtons law of gravity,
 where; 
G = Universal gravitaional constant
r = distance between center of gravities of two objects
m₁,m₂ = masses of thee objects.
F = Gravitational force.
 m = 
 (mass = volume into density.
So when radius is halved, mass drops by a factor of 8,
 m' = 

 = 
 
So in substitution to the equation,

