In the absence of other influences, orbits about Lagrangian points and are dynamically stable so long as the ratio of the masses of the two main objects is greater than about 25. The natural dynamics keep the spacecraft (or natural celestial body) in the vicinity of the Lagrangian point without use of a propulsion system, even when slightly perturbed from equilibrium. These orbits can however be destabilized by other nearby massive objects. For example, orbits around the and points in the Earth–Moon system can last only a few million years instead of billions because of perturbations by the planets.