98943 Torifune

98943 Torifune
Torifune as imaged by Hayabusa2 on 5 July 2026
Discovery
Discovered byLINEAR
Discovery siteLincoln Lab ETS
Discovery date3 February 2001
Designations
Named after
Ame-no-torifune [fr; ja]
2001 CC21
1982 VE13
NEO · Apollo
Orbital characteristics
Epoch 25 February 2023 (JD 2460000.5)
Uncertainty parameter 0
Observation arc40.31 yr (14,725 days)
Earliest precovery date10 November 1982
Aphelion1.259 AU
Perihelion0.806 AU
1.032 AU
Eccentricity0.2192
1.05 yr (383.1 d)
280.856°
0° 56m 23.328s / day
Inclination4.807°
75.519°
179.441°
Earth MOID0.08303 AU (12,421,000 km)
Physical characteristics
Dimensions
  • 840 × 340 m
540 m
5.021516±0.000106 h
301°±35°
+89°+1°
−6°
S or Sq
  • 18.78±0.14
  • 18.71

98943 Torifune (provisional designation 2001 CC21) is an Apollo-type near-Earth asteroid with a diameter of about 450 metres (1,500 feet). It was discovered by the Lincoln Near-Earth Asteroid Research (LINEAR) survey at Socorro, New Mexico, United States on 3 February 2001. It was a flyby target of JAXA's Hayabusa2 spacecraft as a part of its extended mission, which approached as close as 744 m (0.462 mi) from the center of the asteroid on 5 July 2026.

Observations by Hayabusa2 have shown that Torifune is a contact binary asteroid. Telescope observations from Earth had previously indicated that Torifune is an elongated S-type asteroid with a rocky, weathered surface composed mostly of the silicate minerals pyroxene and olivine. It rotates with a period of 5.02 hours and has a small axial tilt of around 5° with respect to Earth's orbit.

Discovery and naming

This asteroid was discovered on 3 February 2001 by the Lincoln Near-Earth Asteroid Research project near Socorro, New Mexico, United States. After several days of further observations by other observatories, the Minor Planet Center (MPC) published the asteroid's discovery on 9 February 2001 and gave it the provisional designation 2001 CC21. The MPC gave the permanent minor planet number of 98943 for the asteroid on 24 February 2005.

After selecting the asteroid as a target for Hayabusa2's extended mission, JAXA held a public naming campaign for the asteroid from December 2023 to May 2024. A committee of Hayabusa2 team members and their children reviewed the 60 names submitted to the campaign and ultimately chose "Torifune". The LINEAR team on behalf of the Hayabusa2 team proposed the name to the International Astronomical Union's Working Group for Small Body Nomenclature, which approved and announced the name on 23 September 2024. "Torifune" is an abbreviation of Ame-no-torifune, the name of a Japanese god and his ship, "which can travel safely at high speed like a bird and steady as a rock."

Orbit and observation

Torifune is a near-Earth asteroid following an elliptical orbit around the Sun, with a semi-major axis of 1.03 astronomical units (AU), an orbital period of 1.05 years, an orbital eccentricity 0.22, and an inclination of 4.8°. Torifune is classified as an Apollo asteroid because it crosses the orbit of Earth with a semi-major axis outside Earth's orbit (>1 AU). At perihelion of 0.81 AU from the Sun, Torifune can come close to Venus. Due to the Yarkovsky effect, the orbit of Torifune is gradually drifting with a transverse acceleration (A2) of (1.3±0.6)×10−14 AU/day2.

The asteroid's orbital period around the Sun is similar to that of Earth's, which allows it to hover near Earth for longer periods of time (giving it a long synodic period). Based on its minimum orbit intersection distances, Torifune can come as close as 0.083 AU (12.4 million km; 7.7 million mi) to Earth and as close as 0.080 AU (12.0 million km; 7.4 million mi) from Venus. During its long-lasting close approaches to Earth, Torifune becomes brighter than apparent magnitude 18, which makes it to observable to small- and medium-class telescopes on Earth. When viewed in a frame rotating with Earth's orbit, Torifune appears to move in an epicyclic path with a slowly drifting center.

Torifune has been observed for over 13 oppositions, with an observation arc spanning more than 40 years as of 2026. Torifune has been identified in two precovery observations, which were both taken by the Siding Spring Observatory on 10 November 1982. The extensive number of observations provide a highly accurate determination of Torifune's orbit, which allows for the prediction of stellar occultations, where Torifune passes in front of a background star. As of 2026, only one occultation by Torifune has been observed; it was observed on 5 March 2024 by only one person in Japan, with 19 others reporting no detection.

Exploration

Animation of Hayabusa2's trajectory from 2014 to 2031, with Torifune's orbit shown in cyan.
  Hayabusa2 ·   Ryugu ·   Earth ·   Torifune ·   1998 KY26

In September 2020, a mission extension for JAXA's Hayabusa2 asteroid sample return probe was selected to do additional flybys of two near-Earth asteroids: Torifune in July 2026 and a rendezvous with 1998 KY26 in July 2031. Hayabusa2 flew by Torifune at an estimated distance of 744 m (0.462 mi) and a very high relative speed of 5 km/s (3.1 mi/s), posing a challenge for the spacecraft's navigation and tracking capabilities during the encounter.

Physical characteristics

Size, shape, and rotation

Telescopic observations have shown that Torifune is smaller than 1 km (1,000 m; 3,300 ft) in diameter, with various studies finding diameter measurements between 300 and 500 m (980 and 1,640 ft) (most likely around 450 m or 1,480 ft). There is a large uncertainty in Torifune's diameter because it is calculated from an uncertain absolute magnitude of 18.78±0.14. As of August 2026, the latest published measurement of Torifune's diameter is 540 m (1,770 ft). This diameter was derived by measurements from Hayabusa2.

Torifune shows periodic variations in brightness as it rotates, which indicates it has an elongated shape. First determined in 2002, photometric measurements of Torifune's light curve show that it has a rotation period of about 5.02 hours. Observations of long-term changes in Torifune's lightcurve suggest that it has a prograde rotation with a low axial tilt of 5°±3° with respect to the ecliptic. In visible light, the brightness of Torifune varies by up to 0.96 magnitudes during one rotation period, which suggests its longest equatorial diameter is roughly 2.44 times as long as its shortest equatorial diameter (equatorial axes ratio b/a=0.41). An approximate shape model derived from Torifune's lightcurve suggests it has dimensions of 840+160
−120 × 320+100
−80 × 340+60
−60 m. The inferred elongation of Torifune's shape allows for the possibility that it might be a contact binary object. On the other hand, near-infrared observations by NEOWISE show smaller variations in brightness, suggesting a less elongated shape with dimensions of 591 m × 461 m × 392 m (1,939 ft × 1,512 ft × 1,286 ft) or an equatorial axes ratio of b/a=0.804±0.060. Observations by Hayabusa2 resulted in measurements for its longest and shortest axis being 840 m × 340 m (2,760 ft × 1,120 ft).

In addition to light curve photometry, Torifune's elongated shape has been inferred from observations of stellar occultations. Only one occultation has been observed, with a single detection giving a chord length of 449 m (1,473 ft). Non-detections by other observers provided additional constraints to Torifune's location and shape, showing that it must be highly elongated with an equatorial axes ratio of b/a=0.37±0.09.

Surface albedo and composition

Visible and near-infrared spectrum of Torifune (blue) compared to the Sq (black), S (green), Q (cyan), and L (yellow) asteroid spectral types

Torifune's diameter and brightness in visible light can be used to derive its geometric albedo,: 4–5  though its uncertain absolute magnitude leads to uncertainties in albedo.: 11  Spectroscopy observations in the near-infrared show that it is a stony S-complex asteroid, with its spectrum best matching with the Sq subtype.: 2  Torifune was previously thought to be a calcium–aluminium-rich L-type asteroid when it was observed spectroscopically for the first time in 2004.: 1 

Torifune's spectral features show a surface composed mainly of the silicate minerals pyroxene and olivine (roughly 40% and 60%, respectively).: 12  The surface's mineralogy resembles that of L and LL chondrites, and it shows signs of moderate space weathering.: 3 : 14  Torifune's spectral features do not vary periodically, suggesting that its surface is broadly homogeneous.: 4 

See also

Notes

References

  1. 1 2 3 4 5 6 7 8 "(98943) Torifune = 1982 VE13 = 2001 CC21". Minor Planet Center. Retrieved 6 April 2023.
  2. 1 2 Spahr, Timothy B. (9 February 2001). "MPEC 2001-C19 : 2001 CC21". Minor Planet Electronic Circular. 2001-C19. Minor Planet Center. Bibcode:2001MPEC....C...19T. Retrieved 6 April 2023.
  3. 1 2 3 4 5 "Small-Body Database Lookup: 98943 (2001 CC21)" (2023-03-05 last obs.). Jet Propulsion Laboratory. Retrieved 6 April 2023.
  4. 1 2 3 4 5 6 7 8 9 10 11 12 13 Hirabayashi, Masatoshi; Hayakawa, Masahiko; Mimasu, Yuya; Hirata, Naru; et al. (10 April 2026). "Overview of Hayabusa2 extended mission's flyby of Near-Earth Asteroid (98943) Torifune". The Planetary Science Journal. 7 (5): 121. arXiv:2604.08832. Bibcode:2026PSJ.....7..121H. doi:10.3847/PSJ/ae5f79.
  5. ↑ "2026/8/5". JAXA はやぶさ２プロジェクト (in Japanese). Retrieved 10 August 2026.
  6. ↑ "2026/8/5". JAXA はやぶさ２プロジェクト (in Japanese). Retrieved 10 August 2026.
  7. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Popescu, Marcel M.; Tatsumi, Eri; Licandro, Javier; Alarcon, Miguel R.; Rodríguez, Javier Rodríguez; Serra-Ricart, Miquel; et al. (February 2025). "Ground-based Characterization of (98943) Torifune 2001 CC21, the Target of the Hayabusa2# Space Mission". The Planetary Science Journal. 6 (2): 42. arXiv:2501.15644. Bibcode:2025PSJ.....6...42P. doi:10.3847/PSJ/ada560.
  8. 1 2 3 4 5 6 7 8 9 Wright, Edward L.; Masiero, Joseph; Mainzer, Amy (December 2025). "NEOWISE Data and Thermophysical Modeling of 98943 Torifune (2001 CC21)". The Planetary Science Journal. 6 (12): 305. arXiv:2512.08181. Bibcode:2025PSJ.....6..305W. doi:10.3847/PSJ/ae21df.
  9. 1 2 Yoshikawa, Makoto; Mimasu, Yuya; Tanaka, Satoshi; Hirabayashi, Masatoshi; Saiki, Takanao; Nakazawa, Satoru; Tsuda, Yuichi; et al. (3 April 2023). Hayabusa2 Extended Mission : Hayabusa2#. 8th IAA Planetary Defense Conference. Vienna, Austria. p. 15. Archived from the original on 7 April 2023.
  10. 1 2 "JAXA | 小惑星探査機「はやぶさ２」、太陽系天体フライバイ探査における最小距離を更新". JAXA | 宇宙航空研究開発機構 (in Japanese). Retrieved 10 August 2026.
  11. ↑ "JAXA | Hayabusa2 captures images of asteroid Torifune". JAXA | Japan Aerospace Exploration Agency. Retrieved 6 July 2026.
  12. ↑ "M.P.C. 53713" (PDF). Minor Planet Circular (53713). Minor Planet Center: 129. 24 February 2005. Retrieved 16 April 2026.
  13. ↑ "2001 CC21 naming campaign". JAXA. Retrieved 3 June 2024.
  14. 1 2 "小惑星2001 CC21の名前が「トリフネ」と決まりました" (in Japanese). JAXA. 25 September 2024. Retrieved 25 September 2024.
  15. 1 2 "WGSBN Bulletin 4, #13" (PDF). WGSBN Bulletin. 4 (3). International Astronomical Union: 19. 23 September 2024. Retrieved 23 September 2024.
  16. 1 2 3 Arimatsu, Ko; Yoshida, Fumi; Hayamizu, Tsutomu; Ida, Miyoshi; Hashimoto, George L.; Abe, Takashi; et al. (July 2024). "Diffraction modelling of a 2023 March 5 stellar occultation by subkilometer-sized asteroid (98943) 2001 CC21". Publications of the Astronomical Society of Japan. 76 (5): 940–949. arXiv:2407.19836. Bibcode:2024PASJ...76..940A. doi:10.1093/pasj/psae060. S2CID 271427751. psae060.
  17. ↑ Hirabayashi, M.; Mimasu, Y.; Sakatani, N.; Watanabe, S.; Tsuda, Y.; Saiki, T.; et al. (August 2021). "Hayabusa2 extended mission: New voyage to rendezvous with a small asteroid rotating with a short period". Advances in Space Research. 68 (3): 1533–1555. arXiv:2104.08660. Bibcode:2021AdSpR..68.1533H. doi:10.1016/j.asr.2021.03.030. S2CID 233297066.
  18. ↑ "Japan's Hayabusa2 probe completes flyby of Torifune asteroid". NHK. 5 July 2026.
  19. 1 2 "2026/8/5". JAXA はやぶさ２プロジェクト (in Japanese). Retrieved 11 August 2026.
  20. ↑ "LCDB Data for (98943) 2001 CC21". Asteroid Lightcurve Database (LCDB). Collaborative Asteroid Lightcurve Link. Retrieved 6 April 2023.
  21. 1 2 3 4 Fornasier, S.; Dotto, E.; Panuzzo, P.; Delbo, M.; Belskaya, I.; Krugly, Y.; et al. (August 2024). "Size, albedo, and rotational period of the Hayabusa2# target (98943) 2001 CC21". Astronomy & Astrophysics. 688: 7. arXiv:2407.13017. Bibcode:2024A&A...688L...7F. doi:10.1051/0004-6361/202450447. S2CID 271270349. L7.
  22. 1 2 3 Bourdelle de Micas, J.; Perna, D.; Fornasier, S.; et al. (January 2025). "Spectral and photometric characterization of (98943) Torifune in preparation for the Hayabusa2# spacecraft flyby". Astronomy & Astrophysics. 693: L19. Bibcode:2025A&A...693L..19B. doi:10.1051/0004-6361/202452498. L19.
  23. 1 2 Geem, Jooyeon; Ishiguro, Masateru; Granvik, Mikael; Naito, Hiroyuki; Akitaya, Hiroshi; Sekiguchi, Tomohiko; et al. (April 2023). "Spectral type and geometric albedo of (98943) 2001 CC21, the Hayabusa2# mission target". Monthly Notices of the Royal Astronomical Society: Letters. 525: L17–L21. arXiv:2304.02917. doi:10.1093/mnrasl/slad073.
  24. "Flyby of asteroid Torifune on July 5, 2026". ISAS. Retrieved 4 February 2026.