The invariant manifolds at infinity of the RTBP and the boundaries of bounded motion Regina Mart\'{\i}nez$^{(1)}$ and Carles Sim\'o$^{(2)}$ $^{(1)}$ Departament de Matem\`atiques, Universitat Aut\`onoma de Barcelona, Bellaterra, Barcelona, Spain $^{(2)}$ Departament de Matem\`atica Aplicada i An\`alisi, Universitat de Barcelona, Barcelona, Spain reginamb@mat.uab.cat, carles@maia.ub.es Abstract The invariant manifolds of the periodic orbit at infinity in the planar circular RTBP are studied. To this end we consider the intersection of the manifolds with the passage through the barycentric pericentre. The intersections of the stable and unstable manifolds have a common even part, which can be seen as a displaced version of the two-body problem, and an odd part which gives rise to a splitting. The theoretical formulas, obtained for Jacobi constant $C$ large enough, are compared to direct numerical computations, showing improved agreement when $C$ increases. A return map to the pericentre passage is derived and using an approximation by standard-like maps one can make a prediction of the location of the boundaries of bounded motion. This result is compared to numerical estimates, again improving for $C$ increasing. Several anomalous phenomena are described.