Im trying to solve (approximately) the following problem: Suppose that i have 2 planets with mass m1 and m2 orbiting around the sun and i take into account the following interactions: a) Interaction between planet 1 and the sun b) Interaction between planet 2 and the sun c) Interaction between planet 1 and planet 2 Where the sun has mas M >> m1,m2 . My physical intuition tells me that this system is similar to a damped harmonical oscillator so at later times the orbital planes of the planets will be aligned, i.e., the angle between the orbital planes will be zero at later times. The problem is that i can't find a book or an article which can help me with this. Does anyone know a good book to start with? or a book with a method to solve this problem?. Finally do you agree with my proposal that the angle between the orbital planes will be zero at later times?.