Close-to-fission dumbbell Jupiter-Trojan (17365) Thymbraeus

Context. Every population of small bodies in the Solar System contains a sizable fraction of multiple systems. Of these, the Jupiter Trojans have the lowest number of known binary systems and they are the least well characterized. Aims: We aim to characterize the reported binary system (17365) Thymbraeus, one of only seven multiple systems of Jupiter Trojans known. Methods: We conducted light curve observing campaigns in 2013, 2015, and 2021 with ground-based telescopes. We modeled these light curves using dumbbell figures of equilibrium. Results: We show that Thymbraeus is unlikely a binary system. Its light curves are fully consistent with a bilobated shape: a dumbbell equilibrium figure. We determine a low density of 830 ± 50 kg m−3, consistent with the reported density of other Jupiter-Trojan asteroids and small Kuiper belt objects. The angular velocity of Thymbraeus is close to fission. If separated, its components would become a similarly sized double asteroid, like the Jupiter-Trojan (617) Patroclus.