This is because the gravitational force is inversely proportional to the square of the distance between two objects. This means that if you double the distance between two objects, the gravitational force between them will be reduced to one-fourth of its original strength.

Here's the formula to illustrate this:

F = G * (m1 * m2) / r²

Where:

* F is the gravitational force

* G is the gravitational constant

* m1 and m2 are the masses of the two objects

* r is the distance between the centers of the two objects

As you can see, the force (F) is directly proportional to the product of the masses and inversely proportional to the square of the distance (r²).