Identifying scattering encounters of near-Earth objects

Assessing the long-term orbital evolution of near-Earth objects is a key component of planetary defense. In many cases, however, reliable predictions are limited by scattering encounters, which are close encounters with the Earth that lead to a rapid loss of predictability, and play a crucial role in defining the effective predictability horizon of an object. In this work, we propose an operational definition of scattering encounter based on simplified two-body dynamics. Building on this framework, we introduce algorithms designed to automatically recognize scattering encounters within standard impact monitoring procedures. A central element of the method is the estimation of the extrema of the post-encounter semi-major axis over the confidence region, for which we develop dedicated techniques. We also discuss these algorithms in the framework of the extended Öpik’s theory of close encounters. The proposed methods are tested with an operational impact monitoring software and are shown to help identify scattering encounters for a variety of real objects.