On the stability of satellites at unstable libration points of sun-planet-moon systems

The five libration points of a sun-planet system are stable or unstable fixed positions at which satellites or asteroids can remain fixed relative to the two orbiting bodies. A moon orbiting around the planet causes a time-dependent perturbation on the system. Here, we address the sense in which invariant structure remains. We employ a transition state theory developed previously for periodically driven systems with a rank-1 saddle in the context of chemical reactions. We find that a satellite can be parked on a so-called time-periodic transition state trajectory – which is an orbit restricted to the vicinity of the libration point L2 for infinitely long time – and investigate the stability properties of that orbit.