Oscillatory Motions in the Restricted 3-body Problem: A functional analytic approach

Abstract: A fundamental question in Celestial Mechanics is to analyze the possible final motions of the Restricted $3$-body Problem, that is, to provide the qualitative description of its complete (i.e. defined for all time) orbits as time goes to infinity. According to the classification given by Chazy back in 1922, a remarkable possible behaviour is that of oscillatory motions, where the motion $q$ of the massless body is unbounded but returns infinitely often inside some bounded region: [ \limsup_{t\to\pm\infty} |q(t)|=\infty\qquad\qquad\text{and}\qquad\qquad \liminf_{t\to\pm\infty} |q(t)|<\infty. ] In contrast with the other possible final motions in Chazy's classification, oscillatory motions do not occur in the $2$-body Problem, while they do for larger numbers of bodies. A further point of interest is their appearance in connection with the existence of chaotic dynamics. In this paper we introduce new tools to study the existence of oscillatory motions and prove that oscillatory motions exist in a particular configuration known as the Restricted Isosceles $3$-body Problem (RI3BP) for almost all values of the angular momentum. Our method, which is global and not limited to nearly integrable settings, extends the previous results \cite{guardia2021symbolic} by blending variational and geometric techniques with tools from nonlinear analysis such as topological degree theory. To the best of our knowledge, the present work constitutes the first complete analytic proof of existence of oscillatory motions in a non perturbative regime.