The paper analyzes a possible cause for the universal behavior of the covariating fluctuations of planet gravity. The consideration based on the idea that the topography fluctuations are governed by a random Markov process leads to universal dependence k^-2 with k being the amplitudes of the j-th spherical harmonic of the terrain profile. This law known as the Kaula's rule is then derived from the solution of the Fokker—Plank equation for the fluctuations of the terrain profile as the function of the horizontal coordinate. The respective diffusivities for Earth and Venus are retrieved from the existing data.