Analysis of pitchfork bifurcations and symmetry breaking in the elliptic restricted three-body problem

A unified framework is proposed to quantitatively characterize pitchfork bifurcations and associated symmetry breaking in the elliptic restricted three-body problem (ERTBP). It is known that planar/vertical Lyapunov orbits and Lissajous orbits near the collinear libration points undergo pitchfork bifurcations with varying orbital energy. These bifurcations induce symmetry breaking, generating bifurcated families including halo/quasi-halo orbits, axial/quasi-axial orbits, and their corresponding invariant manifolds. Traditional semi-analytical methods for constructing halo orbits, based on resonant bifurcation mechanisms, have obstacles in fully exploiting the intrinsic symmetry breaking characteristics in pitchfork bifurcations. In this paper, a unified trigonometric series-based framework is proposed to analyze these bifurcated families from the perspective of coupling-induced bifurcation mechanisms. By introducing a coupling coefficient and various bifurcation equations into the ERTBP, different symmetry breaking is achieved when the coupling coefficient is non-zero. This unified semi-analytical framework captures bifurcations of both periodic/quasi-periodic and transit/non-transit orbits. Furthermore, it reveals that pitchfork bifurcation solutions in the ERTBP fundamentally depend solely on the orbital eccentricity and three amplitude parameters of the system's degrees of freedom, governing both the elliptic direction and the hyperbolic one.