Presentation Information
[PPS03-P04]Surface Color Properties of the Hayabusa2# Target Asteroid “Torifune” from Simultaneous Three-Filter Photometric Observations with the Seimei Telescope
*Kazuya Doi, Seiko Takagi1, Tomohiko Sekiguchi2, Daisuke Kuroda3, Seitaro Urakawa3, Jin Beniyama4,5, Masateru Ishiguro6, Jooyeon Geem7, Hiroki Sensyu8 (1.Hokkaido University, Department of Cosmosciences, 2.Hokkaido University of Education, 3.Japan Spaceguard Association, 4.University of Tokyo, 5.Observatoire de la Côte d'Azur, 6.Seoul National University, 7.Luleå University of Technology , 8.Chiba Tech university)
Keywords:
Asteroid,Near-Earth Asteroid,Planetary Defense,Hayabusa2#,Ground-based observation,Photometric observation
Near-Earth Asteroid (NEA) Torifune is the next target of the JAXA Hayabusa2# mission. During this mission, the spacecraft will perform a high-speed flyby of this NEA at an extremely close distance of ~1 km with a relative velocity of ~5 km/s [Tsuda et al., 2025]. To ensure the success of the flyby observations, it is essential to properly pre-set the onboard cameras of Hayabusa2, and accurate information on the surface color properties of Torifune is essential. Moreover, because asteroids rotate with their own periods, it is necessary to obtain color information at different rotational phases in advance to determine whether the surface is homogeneous or heterogeneous.
The Seimei telescope at Okayama Observatory, owned by Kyoto University and operated for open use by the National Astronomical Observatory of Japan, has an effective diameter of 3.8 m composed of 18 segmented mirrors. Its large light-collecting power, the largest among optical telescopes in East Asia, is optimal for observations of small and faint asteroids. Using the Tricolor CMOS Camera and Spectrograph; TriCCS, we conducted simultaneous three-color photometric observations and obtained high time-resolution and high-accuracy color properties at each rotational phase.
The data from several nights were folded using the previously determined rotational period to construct multi-color light curves [Popescu et al., 2025]. The derived color indices are consistent with typical S-type values, and no significant variations were detected at different rotational phases. We therefore conclude that Torifune has globally homogeneous surface color properties. The reflectance spectrum derived from the color indices indicates an Sq-type classification, between S-type and Q-type, suggesting a moderately space-weathered surface [Binzel et al., 2010]. In addition, the spectral slope at each phase angle shows the characteristic phase-reddening trend of S-type asteroids [Perna et al., 2018]. In particular, color data obtained at low phase angles are important for the flyby observations. We report the detailed color properties of Torifune.
The Seimei telescope at Okayama Observatory, owned by Kyoto University and operated for open use by the National Astronomical Observatory of Japan, has an effective diameter of 3.8 m composed of 18 segmented mirrors. Its large light-collecting power, the largest among optical telescopes in East Asia, is optimal for observations of small and faint asteroids. Using the Tricolor CMOS Camera and Spectrograph; TriCCS, we conducted simultaneous three-color photometric observations and obtained high time-resolution and high-accuracy color properties at each rotational phase.
The data from several nights were folded using the previously determined rotational period to construct multi-color light curves [Popescu et al., 2025]. The derived color indices are consistent with typical S-type values, and no significant variations were detected at different rotational phases. We therefore conclude that Torifune has globally homogeneous surface color properties. The reflectance spectrum derived from the color indices indicates an Sq-type classification, between S-type and Q-type, suggesting a moderately space-weathered surface [Binzel et al., 2010]. In addition, the spectral slope at each phase angle shows the characteristic phase-reddening trend of S-type asteroids [Perna et al., 2018]. In particular, color data obtained at low phase angles are important for the flyby observations. We report the detailed color properties of Torifune.