Answer:
When the object is infinitely far away from the planet, or when the planet's mass is zero (which is much less likely).
Explanation:
Using the formula for gravitational force:
Fg = GMm/r^2
Using Newton's 2nd law, F=ma, we can rewrite this equation as
mg = GMm/r^2
cancel m from both sides
g = GM/r^2
the acceleration due to gravity is zero when the mass of the planet is zero, or the object is an infinite distance away from the planet. G is a constant.
