Letter to the Editor

Spectral and photometric characterization of (98943) Torifune in preparation for the Hayabusa2# spacecraft flyby

¹ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, I-00078 Monte Porzio Catone, Italy
² LESIA, Observatoire de Paris, Université Paris Cité, Université PSL, CNRS, Sorbonne Université, 5 place Jules Janssen, 92195 Meudon, France
³ Institut Universitaire de France (IUF), 1 rue Descartes, 75231 Paris Cedex 05, France
⁴ Department of Physics and Astronomy, Seoul National University, Gwanak-gu, Seoul, 08826 Republic of Korea
⁵ SNU Astronomy Research Center, Seoul National University, Gwanak-gu, Seoul, 08826 Republic of Korea
⁶ Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa, 252-5210 Japan
⁷ Department of Computer Science and Engineering/Division of Information Systems, The University of Aizu, Aizu-Wakamatsu, Fukushima, 965-8580 Japan
⁸ Japan Spaceguard Association, Bisei Spaceguard Center 1716-3 Okura, Bisei, Ibara, Okayama, 714-1411 Japan
⁹ INAF Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere 100, I-00133 Rome, Italy
¹⁰ Georgia Institute of Technology, Atlanta, GA, USA

^⋆ Corresponding author; jules.bourdelledemicas@inaf.it

Received: 4 October 2024
Accepted: 27 December 2024

Abstract

Context. After a successful sample-return mission to the asteroid (162173) Ryugu, the Hayabusa2 spacecraft is currently on its way to encounter two near-Earth asteroids: (98943) Torifune (formerly known as 2001 CC21) and 1998 KY26.

Aims. In this article, we study the asteroid (98943) Torifune, the first object that is to be visited by the spacecraft during its extended mission. To prepare for its encounter with the spacecraft, it is crucial to study this object from Earth. We conducted several ground-based observations to characterize this asteroid and understand its mineralogy.

Methods. In January and February 2023, we carried out spectroscopic and photometric observations at the 2.56 m Nordic Optical Telescope, in the visible and near-infrared ranges, covering different rotational phases of the asteroid.

Results. Based on spectra analysis in the visible and near-infrared ranges, confirmed by the color studies, we determined that Torifune belongs to the Sq-type, according the Bus-DeMeo taxonomy. Assuming this taxonomy and its equivalent diameter (D ∼ 465 ± 15 m), we estimated the mass of this asteroid to be 1.81 ± 0.11  ×  10¹¹ kg. In term of mineralogy, we found a close match with ordinary L chondrites.

Conclusions. As our observations covered almost a complete rotation phase, we did not find any spectral variation at different rotational phases, meaning that there is no substantial heterogeneities on Torifune’s surface. We compared the spectral slope of (98943) Torifune with that of the S-complex members of the Lucienne family. However, further studies, especially dynamical ones, are needed to confirm whether this object originates from the Lucienne family.