To do this we would first need to write down the interactions in this system as a many body problem which interact by gravity. We then have to redefine this problem as a sum of single-body interactions. To do this we have to add to the kinetic energy of the planets the interaction of each planet with a stationary sun, this is the external potential. Second, we have to calculate the gracitational interactions between a given planet and the average static distribution of all the other planets, this is the Hartree term. And finally, add an unkown external correlation functional that bridges the gap between the single body and the many body problem.