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98943 Torifune

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98943 Torifune
Discovery[1][2]
Discovered byLINEAR
Discovery siteLincoln Lab ETS
Discovery date3 February 2001
Designations
(98943) Torifune
2001 CC21
1982 VE13[1]
NEO · Apollo
Orbital characteristics[3]
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
465±15 m[4]
5.02124±0.00001 h[4]
0.216±0.016[4]
S
18.94±0.05[4] · 18.74[3][1]

98943 Torifune (provisional designation 2001 CC21) is a stony near-Earth asteroid of the Apollo group, with a diameter of about 500 metres (1,600 feet). It was discovered by the Lincoln Near-Earth Asteroid Research (LINEAR) survey at Socorro, New Mexico on 3 February 2001.[1] It is an upcoming flyby target of JAXA's Hayabusa2 extended mission, which will approach less than 100 km (62 mi) from the asteroid in July 2026.[5][6]

Discovery and naming

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This asteroid was discovered on 3 February 2001 by the Lincoln Near-Earth Asteroid Research project near Socorro, New Mexico and given the provisional designation 2001 CC21.[1] 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.[7] The winning name "Torifune" was officially announced by the International Astronomical Union's Working Group for Small Body Nomenclature on 23 September 2024.[8] "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."[8]

Physical characteristics

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Observations of Torifune's infrared thermal emission by the Spitzer Space Telescope in 2005 show that it is a small asteroid with a mean diameter of 465 m (1,526 ft).[4]: 1  The asteroid's diameter and brightness in visible light indicate it has a geometric albedo of 21.6%, which agrees with near-infrared spectroscopy observations which show that Torifune is a stony S-type asteroid composed of silicates and traces of pyroxene.[4]: 4–5 [9] Torifune was previously thought to be a calcium–aluminium-rich L-type asteroid when it was observed spectroscopically for the first time in 2004, but this was disproven by later spectroscopic observations in 2005 and 2023.[4]: 1 [9]

Photometric measurements of Torifune's light curve, or brightness over time, show that it is an elongated asteroid whose brightness fluctuates 0.75–1.1 magnitudes for every time it rotates in 5.02 hours.[4]: 2  The large light curve amplitude of Torifune indicates that its longest axis is at least 1.7 times longer than its shortest axis–this is suggestive of Torifune having either a contact binary shape or a single elongated shape.[4]: 3  Torifune's rotation period was first measured in January 2002, and later observations in 2003 between 2024 secured this period and refined it to 5.02124±0.00001 hours.[10][4]: 2 

On 5 March 2023, 20 people on the Honshu and Shikoku islands in Japan observed a stellar occultation by Torifune. Only one person recorded a positive detection of the occultation; the resulting chord length of Torifune was 449 m (1,473 ft).[4]: 4  The non-detections by the other observers indicate Torifune must be highly elongated with a long axis 2.7 times longer than its shortest axis.[11][a]

Exploration

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Animation of Hayabusa2 orbit - Extended mission
  Hayabusa2 ·   162173 Ryugu ·   Earth ·   Sun ·   98943 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.[5][6] Hayabusa2 will flyby within 100 km (62 mi) of Torifune at a very high relative speed of 5 km/s (3.1 mi/s), which will pose a challenge for the spacecraft's navigation and tracking capabilities during the encounter.[6]

See also

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Notes

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  1. ^ Arimatsu et al. (2024) give b/a = 0.37±0.09 for Torifune's ellipse axis ratio.[11] Inverting this ratio gives a/b = 1/0.37 ≈ 2.7.

References

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  1. ^ a b c d e "(98943) Torifune = 1982 VE13 = 2001 CC21". Minor Planet Center. Retrieved 6 April 2023.
  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. ^ a b "Small-Body Database Lookup: 98943 (2001 CC21)" (2023-03-05 last obs.). Jet Propulsion Laboratory. Retrieved 6 April 2023.
  4. ^ a b c d e f g h i j k 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.
  5. ^ a b 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.
  6. ^ a b c 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.
  7. ^ "2001 CC21 naming campaign". JAXA. Retrieved 3 June 2024.
  8. ^ a b "WGSBN Bulletin 4, #13" (PDF). WGSBN Bulletin. 4 (3). International Astronomical Union: 19. 23 September 2024. Retrieved 23 September 2024.
  9. ^ a b 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.
  10. ^ "LCDB Data for (98943) 2001 CC21". Asteroid Lightcurve Database (LCDB). Collaborative Asteroid Lightcurve Link. Retrieved 6 April 2023.
  11. ^ a b 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: 10. arXiv:2407.19836. Bibcode:2024PASJ..tmp...71A. doi:10.1093/pasj/psae060. S2CID 271427751. psae060.{{cite journal}}: CS1 maint: bibcode (link)
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