“…In the following, we shall use the Delaunay variables for studying the periodic orbits of the Hamiltonian system associated with the Hamiltonian (1), which is called the zonal J 2 + J 3 problem; see [13][14][15][16][17][18] for more details on the Delaunay variables and this astrophysical problem. Thus, if {l, g, k, L, G, K} are the action angle coordinates of Delaunay, where l is the mean anomaly, g is the argument of the periapsis of the unperturbed elliptical orbit measured in the invariant plane, k is the longitude of the ascending node, L is the square root of the major semi-axis of the unperturbed elliptic orbit, G is the modulus of the total angular momentum, and K is the third component of the angular momentum, then the Hamiltonian (1) has the form:…”