Female Speaker: A Planet's gravity is determined by its mass and by the distance from its surface to its center of mass. The mass of the moon is only one ADF the mass of earth, but its gravity is much more than one ADF the earth's gravity, because the moons surface is four times closer to its center of mass. As a result the moons gravitational force is only one-sixth as strong as the earth, so objects may one- sixth as much on the moon. The weight of an object on any planet in our solar system can be determined by mathematical formula, choose the planet to compare the changes and weight, for a one hundred pound boy and a fifteen pound dog sun.