Analytical estimates for heliocentric escape of satellite ejecta

Abstract

We present a general analytic framework to assess whether impact ejecta launched from the surface of a satellite can escape the gravitational influence of the planet–satellite system and enter heliocentric orbit. Using a patched-conic approach and defining the transition to planetocentric space via the Hill sphere or sphere of influence, we derive thresholds for escape in terms of the satellite-to-planet mass ratio and the ratio of the satellite’s orbital speed to its escape speed. We identify three dynamical regimes for ejecta based on residual speed and launch direction. We complement this analysis with the circular restricted three-body problem, deriving a necessary escape condition from the Jacobi integral at $L_2$ and showing that it is consistent with the patched–conic thresholds. Applying our model to the Earth–Moon system reveals that all three outcomes — bound, conditional, and unbound — are accessible within a narrow range of launch speeds. This behavior is not found in other planetary satellite systems, but may occur in some binary asteroids. The framework also shows that the Moon’s tidal migration has not altered its propensity to produce escaping ejecta, reinforcing the plausibility of a lunar origin for some near-Earth asteroids.