Japan’s Hayabusa2 Completes Daring 800-Meter Flyby of Asteroid Torifune
Japan’s Hayabusa2 spacecraft executed a historic close flyby of the asteroid Torifune on July 5, passing within 800 meters (0.5 miles) of the space rock at a speed of 10,000 miles per hour, according to the Japan Aerospace Exploration Agency (JAXA). This maneuver, described as as difficult as hitting a 1-yen coin placed in Hokkaido from Okinawa
by mission team leader Yuya Mimasa, marked a critical test of the probe’s navigation and scientific capabilities.
Asteroid Torifune: A Contact Binary Revealed
Torifune, discovered in 2001, is an S-Type asteroid approximately 1,500 feet long, part of the Apollo family of near-Earth asteroids that cross Earth’s orbit. The flyby confirmed it as a contact binary—a dual-lobed object formed by two bodies that have gravitationally merged. This structure, common among asteroids and comets, was unexpected to mission scientists. We did not imagine such a contact binary,
said Yoshikawa, a former Hayabusa2 mission manager, during a scientific conference. The probe’s Optical Navigation Camera captured high-resolution images of the asteroid’s surface, revealing silicate minerals and a peanut-like shape.
The flyby also demonstrated the first successful use of LIDAR (Laser Imaging Detection and Ranging) during an asteroid encounter, according to the mission team. Instruments like the Near Infrared Spectrometer and laser altimeter provided data on Torifune’s composition and topography, though only 25MB of the 300MB total data was immediately downloaded. Scientists will analyze the remaining data over months to study the asteroid’s geological history and potential hazards.
Technical Challenges and Risk Assessment
The flyby posed significant risks due to uncertainties about Torifune’s size and trajectory. JAXA engineers estimated the asteroid could measure up to 1,400 meters by 400 meters, though its actual dimensions remained unclear. The spacecraft relied on terrestrial guidance systems for three hours before the encounter, with mission control in Japan coordinating commands over 100 million kilometers.
The proximity required precise maneuvering to avoid collision. The spacecraft’s systems and instruments were not designed for high-speed tracking,
noted a source from the mission. Despite these challenges, Hayabusa2 performed flawlessly, with JAXA officials stating it responded to all instructions from land-based mission control.
The mission’s success highlights Japan’s advancements in deep-space navigation and planetary defense technologies.
Future Missions: From Torifune to 1998 KY26
Hayabusa2’s next target is the small, rapidly rotating asteroid 1998 KY26, scheduled for a 2031 rendezvous. At just 36 feet in diameter, 1998 KY26 presents a new set of challenges, including the spacecraft’s aging systems. By 2031, Hayabusa2’s ion engines will be depleted, and its sensors will have suffered radiation damage. The mission’s goals for 1998 KY26 include entering orbit, deploying a target marker, and attempting a landing—likely on one of the asteroid’s poles.
This final phase of the mission aims to advance understanding of asteroid diversity and improve planetary defense strategies. JAXA’s Masaki Fujimoto emphasized that the Torifune flyby demonstrated the technology to change the orbit of an asteroid heading towards the Earth,
underscoring the broader implications for mitigating cosmic threats.
Context: A Growing Focus on Near-Earth Objects
While Hayabusa2’s flyby of Torifune garnered attention, it occurred alongside China’s Tianwen-2 mission, which recently arrived at the quasi-moon asteroid Kamoʻoalewa. Discovered in 2016, Kamoʻoalewa is believed to be a lunar fragment and will be studied for several months before sample return in 2027. Though not directly related to Hayabusa2, these missions reflect a global push to understand near-Earth objects and their potential risks. For Hayabusa2, the Torifune encounter represents both a scientific milestone and a precursor to its final challenge. As the spacecraft continues its journey, it carries the legacy of Japan’s leadership in asteroid exploration, blending technological innovation with the imperative to safeguard Earth from cosmic impacts.
