When the horseshoe fits: Characterizing 2023 FY3 with the 10.4 m Gran Telescopio Canarias and the Two-meter Twin Telescope

Context. The Arjuna asteroid belt is loosely defined as a diverse group of small asteroids that follow dynamically cold, Earth-like orbits. Most of them are not actively engaged in resonant, co-orbital behavior with Earth. Some of them experience temporary but recurrent horseshoe episodes. Objects in horseshoe paths tend to approach Earth at a low velocity, leading to captures as Earth's temporary satellites or mini-moons. Four such objects have already been identified: 1991 VG, 2006 RH₁₂₀, 2020 CD₃, and 2022 NX₁. Here, we focus on 2023 FY₃, a recent finding, the trajectory of which might have a co-orbital status and perhaps lead to temporary captures.
Aims: We want to determine the physical properties of 2023 FY₃ and explore its dynamical evolution.
Methods: We carried out an observational study of 2023 FY₃ using the OSIRIS camera spectrograph at the 10.4 m Gran Telescopio Canarias, to derive its spectral class, and time-series photometry obtained with QHY411M cameras and two units of the Two-meter Twin Telescope to investigate its rotational state. N-body simulations were also performed to examine its possible resonant behavior.
Results: The visible reflectance spectrum of 2023 FY₃ is consistent with that of an S-type asteroid; its light curve gives a rotation period of 9.3±0.6 min, with an amplitude of 0.48±0.13 mag. We confirm that 2023 FY₃ roams the edge of Earth's co-orbital space.
Conclusions: Arjuna 2023 FY₃, an S-type asteroid and fast rotator, currently exhibits horseshoe-like resonant behavior and in the past experienced mini-moon engagements of the temporarily captured flyby type that may repeat in the future. The spectral type result further confirms that mini-moons are a diverse population in terms of surface composition.