Prospects of a New <i>L</i> ₅ Trojan Flyby Target for the Lucy Mission

Abstract NASA’s Lucy spacecraft is en route to conduct the first close encounter with Jupiter’s Trojans. While most scheduled flybys lie in the L 4 cloud, the only L 5 target is the Patroclus–Menoetius binary. Since each flyby offers unique insights into target and population properties unattainable from Earth, we examine the feasibility of including an additional, yet unknown, L 5 target while minimizing the impact on Lucy’s primary mission. We use the background L 5 Trojans brighter than the completeness limit to model their absolute magnitude, spatial, and orbital distributions. A semianalytical approach estimates the number of Trojans accessible to Lucy for a given Δ v budget in both pre- and post-Patroclus scenarios. Our results indicate that, while it is unlikely that any suitable Trojan lies on Lucy’s nominal path, a moderate Δ v investment (35–50 m s −1 ) could enable a subkilometer (500–700 m) flyby prior to the Patroclus encounter. Post-Patroclus, the likelihood of a similar flyby is ∼60% for Δ v ∼ 50 m s −1 . Simulations with synthetic Trojans reveal that potential targets cluster near the node opposite the encounter window, producing an optimal search period in late 2026 for both scenarios. Surveying the densest 10% of this region would require under 5 nights with the Subaru Hyper Suprime-Cam or under 2 nights with Rubin, using shift-and-stack techniques. A successful subkilometric flyby would expand Lucy’s Trojan target size range and provide new constraints on collisional evolution and the long-standing asymmetry in the L 4 / L 5 clouds. This nodal-clustering strategy could guide target searches in future Lucy extensions or other planetary flyby missions.