The Gravitational force between two point masses separated by a distance $$r$$ is proportional to $$\dfrac{1}{r^2}$$, just like the electric force between two point charges. Because of this similarity between gravitatonal and electrical interactions, there is also a Gauss's law for gravitation. Let $$g$$ be the acceleration due to gravity caused by point mass $$m$$ at the origin so that $$g = \dfrac{-Gm}{r^2} \hat{r}$$. Consider a spherical Gaussian surface with radius $$r$$ centered on this point mass.