Lyapunov time

The Lyapunov time of a dynamical system is a timescale after which it is unpredictable, i.e., chaotic. Within astronomy, systems of orbiting bodies (such as the Earth and the Moon) are subject to such a timescale. The Lyapunov exponent is the timescale's inverse. Theory provides methods to calculate Lyapunov times, but the calculations can be unstable and producing a consistent, repeatable determination is a challenge. Some example determinations:

Lack of a consensus proof of the solar system's long-term stability despite a presumed lifetime of gigayears has been a motivation for research.