It also doubles The gravitational force between two masses is expressed as: F = G*m1*m2/r^2 where F = Force between the two masses m1 = Mass of object 1 m2 = Mass of object 2 r = distance between centers of object 1 and object 2 G = Gravitational constant The exact values of G, m1, m2, and r don't matter since all except for m1 is held constant. And when m1 suddenly doubles, the force attracting the two object to each other also doubles.