The Moon as a possible source for Earth's co-orbital bodies

Abstract

There is a growing number of Earth's co-orbital bodies being discovered. At least five of them are known to be temporarily in quasi-satellite orbits. One of those, 469219 Kamo'oalewa, was identified as possibly having the same composition as the Moon. We explore the conditions necessary for lunar ejecta to evolve into Earth's co-orbital bodies, with particular attention to the formation of quasi-satellite orbits. We systematically investigate the parameter space of ejection velocity and geographic launch location across the entire lunar surface. The study employs numerical simulations of the four-body problem (Sun-Earth-Moon-particle) with automated classification methodology for identifying all co-orbital states. Particles are ejected from randomly distributed points covering the entire lunar surface with velocities ranging from 1.0 to 2.6 times the Moon's escape velocity. Trajectories co-orbital to Earth are found to be a common outcome, with approximately 6.15% of all simulated particles evolving into Earth co-orbital motion and 1.92% specifically exhibiting quasi-satellite behavior. We identify an optimal ejection velocity (1.2 times escape velocity) for quasi-satellite production, yielding over 6% conversion efficiency at this specific velocity. The spatial distribution of successful ejections shows a strong preference for the equatorial regions of the trailing hemisphere. Collisions with Earth or the Moon occur for only 4% of the sample. Our results strengthen the plausibility of lunar origin for Earth's co-orbital bodies, including quasi-satellites like Kamo'oalewa and 2024 PT5. We identify both "prompt" and "delayed" co-orbital formation mechanisms, with a steady-state production regime that could explain the presence of lunar-derived objects in Earth's co-orbital regions despite the infrequent occurrence of major lunar impacts capable of launching meter-scale fragments.