98943 Torifune

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 {{mp|2001 CC|21}}. 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.{{cite web |url=https://www.hayabusa2.jaxa.jp/en/topics/20231206_CC21Camp_e/ |title=2001 CC21 naming campaign |publisher=JAXA |access-date=3 June 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."

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 {{cvt|465|m|ft}}.{{rp|page=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.{{rp|page=4–5}} 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.{{rp|page=1}}

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.{{rp|page=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.{{rp|page=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 {{val|5.02124|0.00001}} hours.{{rp|page=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 {{cvt|449|m|ft}}.{{rp|page=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.{{efn|Arimatsu et al. (2024) give b/a {{=}} {{val|0.37|0.09}} for Torifune's ellipse axis ratio. Inverting this ratio gives a/b {{=}} 1/0.37 ≈ 2.7.}}

File:Animation of Hayabusa2 orbit - extended mission.webm}}{{·}}{{legend2|lime|162173 Ryugu}}{{·}}{{legend2|Royalblue|Earth}}{{·}}{{legend2|yellow|Sun}}{{·}}{{legend2|cyan|98943 Torifune}}{{·}}{{legend2|gold|{{mpl|1998 KY|26}}}}]]

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 {{mpl|1998 KY|26}} in July 2031. Hayabusa2 will flyby within {{cvt|100|km|mi}} of Torifune at a very high relative speed of {{cvt|5|km/s|mi/s}}, which will pose a challenge for the spacecraft's navigation and tracking capabilities during the encounter.

• 162173 Ryugu, Hayabusa2{{'}}s asteroid sample return target in 2018
• {{mpl|1998 KY|26}}, second asteroid flyby target of Hayabusa2 in 2031

{{notelist}}

{{reflist|refs=

{{cite web

|type = 2023-03-05 last obs.

|title = Small-Body Database Lookup: 98943 (2001 CC21)

|url = https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=20098943

|publisher = Jet Propulsion Laboratory

|accessdate = 6 April 2023}}

{{cite web

|title = (98943) Torifune = 1982 VE13 = 2001 CC21

|url = https://www.minorplanetcenter.net/db_search/show_object?object_id=98943

|publisher = Minor Planet Center

|accessdate = 6 April 2023}}

{{cite web

|title = LCDB Data for (98943) 2001 CC21

|url = https://minplanobs.org/mpinfo/php/lcdbsummaryquery.php

|work = Asteroid Lightcurve Database (LCDB)

|publisher = Collaborative Asteroid Lightcurve Link

|accessdate = 6 April 2023}}

{{cite journal

|title = MPEC 2001-C19 : 2001 CC21

|url = https://minorplanetcenter.net/mpec/K01/K01C19.html

|first = Timothy B. |last = Spahr

|journal = Minor Planet Electronic Circular

|publisher = Minor Planet Center

|date = 9 February 2001

|volume = 2001-C19

|accessdate = 6 April 2023

|bibcode = 2001MPEC....C...19T}}

{{cite journal

|display-authors = etal

|first1 = M. |last1 = Hirabayashi

|first2 = Y. |last2 = Mimasu

|first3 = N. |last3 = Sakatani

|first4 = S. |last4 = Watanabe

|first5 = Y. |last5 = Tsuda

|first6 = T. |last6 = Saiki

|title = Hayabusa2 extended mission: New voyage to rendezvous with a small asteroid rotating with a short period

|journal = Advances in Space Research

|date = August 2021

|volume = 68

|issue = 3

|pages = 1533–1555

|doi = 10.1016/j.asr.2021.03.030

|arxiv = 2104.08660

|bibcode = 2021AdSpR..68.1533H|s2cid = 233297066 }}

{{cite conference

|display-authors = etal

|first1 = Makoto |last1 = Yoshikawa

|first2 = Yuya |last2 = Mimasu

|first3 = Satoshi|last3 = Tanaka

|first4 = Masatoshi |last4 = Hirabayashi

|first5 = Takanao |last5 = Saiki

|first6 = Satoru |last6 = Nakazawa

|first7 = Yuichi |last7 = Tsuda

|title = Hayabusa2 Extended Mission : Hayabusa2#

|url = https://az659834.vo.msecnd.net/eventsairwesteuprod/production-atpi-public/9f51bd9e02dc448886f07de3809c04a4

|conference = 8th IAA Planetary Defense Conference

|location = Vienna, Austria

|date = 3 April 2023

|pages = 15

|archive-url = https://web.archive.org/web/20230407053627/https://az659834.vo.msecnd.net/eventsairwesteuprod/production-atpi-public/9f51bd9e02dc448886f07de3809c04a4

|archive-date = 7 April 2023

|url-status = live}}

{{cite journal

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|first4 = Hiroyuki |last4 = Naito

|first5 = Hiroshi |last5 = Akitaya

|first6 = Tomohiko |last6 = Sekiguchi

|title = Spectral type and geometric albedo of (98943) 2001 CC21, the Hayabusa2# mission target

|journal = Monthly Notices of the Royal Astronomical Society: Letters |date = April 2023

|volume = 525 |pages = L17–L21 |doi = 10.1093/mnrasl/slad073 |doi-access = free |arxiv = 2304.02917

}}

{{cite journal

|display-authors = etal

|first1 = Ko |last1 = Arimatsu

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|first4 = Miyoshi |last4 = Ida

|first5 = George L. |last5 = Hashimoto

|first6 = Takashi |last6 = Abe

|title = Diffraction modelling of a 2023 March 5 stellar occultation by subkilometer-sized asteroid (98943) 2001 CC21

|journal = Publications of the Astronomical Society of Japan

|date = July 2024

|volume = 76 |issue = 5 |id = psae060

|pages = 940–949

|doi-access = free

|doi = 10.1093/pasj/psae060

|arxiv = 2407.19836

|bibcode = 2024PASJ...76..940A

|s2cid = 271427751}}

{{cite journal

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|first5 = I. |last5 = Belskaya

|first6 = Y. |last6 = Krugly

|title = Size, albedo, and rotational period of the Hayabusa2# target (98943) 2001 CC21

|journal = Astronomy & Astrophysics

|date = August 2024

|volume = 688

|id = L7

|pages = 7

|doi-access = free

|doi = 10.1051/0004-6361/202450447

|arxiv = 2407.13017

|bibcode = 2024A&A...688L...7F

|s2cid = 271270349}}

{{cite journal

|title = WGSBN Bulletin 4, #13

|url = https://www.wgsbn-iau.org/files/Bulletins/V004/WGSBNBull_V004_013.pdf

|journal = WGSBN Bulletin

|publisher = International Astronomical Union

|volume = 4

|issue = 3

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|date = 23 September 2024

|accessdate = 23 September 2024}}

{{cite web

|title = 小惑星2001 CC21の名前が「トリフネ」と決まりました

|url = https://www.hayabusa2.jaxa.jp/topics/20240925_2001_CC21/index.html

|publisher = JAXA

|language = ja

|date = 25 September 2024

|accessdate = 25 September 2024}}

}}

• {{cite web|title=Asteroid Explorer Hayabusa2|url=https://www.isas.jaxa.jp/en/missions/spacecraft/current/hayabusa2.html|work=Institute of Space and Astronomical Science|publisher=Japan Aerospace Exploration Agency (JAXA)}}
• {{AstDys|98943}}
• {{JPL small body}}

{{Minor planets navigator| |number=98943| |PageName=98943 Torifune | }}

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Category:Apollo asteroids

Category:Discoveries by LINEAR

Torifune

Category:S-type asteroids

Category:Minor planets to be visited by spacecraft

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