98943 Torifune

This asteroid was discovered on 3 February 2001 by the Lincoln Near-Earth Asteroid Research project near Socorro, New Mexico, United States.^[1] 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.^[2] The MPC gave the permanent minor planet number of 98943 for the asteroid on 24 February 2005.^[9]

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.^[10] A committee of Hayabusa2 team members and their children reviewed the 60 names submitted to the campaign and ultimately chose "Torifune".^[11] 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.^[11][12] "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."^[12]

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°.^[3] 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).^[4][6] At perihelion of 0.81 AU from the Sun, Torifune can come close to Venus.^[1][3] 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.^[3][4]

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).^[5] 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.^[1] 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.^[6] When viewed in a frame rotating with Earth's orbit, Torifune appears to move in an epicyclic path with a slowly drifting center.^[5]

Torifune has been observed for over 13 oppositions, with an observation arc spanning more than 40 years as of 2026^[update].^[1] Torifune has been identified in two precovery observations, which were both taken by the Siding Spring Observatory on 10 November 1982.^[1][5] The extensive number of observations provide a highly accurate determination of Torifune's orbit,^[5] which allows for the prediction of stellar occultations, where Torifune passes in front of a background star.^[13] As of 2026^[update], 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.^[4]

• 
  Diagram showing the orbits of Torifune (white) and the four inner planets
• 
  Top views of Torifune's orbit and Hayabusa2's trajectory from December 2020 to July 2026, as viewed in a frame rotating with Earth's orbit (a; left) and in a stationary frame (b; right)

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.^[14][7] 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.^[7]

• 162173 Ryugu, Hayabusa2's asteroid sample return target in 2018
• 1998 KY26, second asteroid flyby target of Hayabusa2 in 2031
• List of minor planets and comets visited by spacecraft