# 98943 Torifune

98943 Torifune (provisional designation 2001 CC$_{21}$) 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. 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.

## Discovery and naming

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 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. 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."

## Physical characteristics

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).$^{:1}$ 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.$^{:4–5}$ 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.$^{:1}$
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.$^{:2}$ 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.$^{:3}$ 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.$^{:2}$
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).$^{:4}$ 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.

## Exploration

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 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.