The newly published study shows that asteroid 1998 KY26, the next target of Japan’s Hayabusa2 spacecraft, is far smaller and spins much faster than scientists believed. This discovery matters now because the spacecraft is already on its way, and its entire 2031 mission strategy depends on accurate knowledge of the asteroid’s size, brightness, and behavior. The study reveals an 11 meter object spinning once every 5.35 minutes, forcing scientists to rethink everything from landing plans to safety operations. s41467-025-63697-4
Fast Facts
Study: New observations reveal asteroid 1998 KY26 is only 11 meters wide and spins every 5.35 minutes.
Why It Matters: These findings change key plans for the Hayabusa2 mission arriving in 2031.
Key Insight: The asteroid is brighter, faster, and structurally weaker than earlier believed.
Impact: Results improve planetary-defense models and prepare scientists for the first visit to a tiny fast-rotating asteroid.
Scientists found that 1998 KY26 is only about 11 meters wide, not 30 meters as earlier radar data suggested. It also spins in 5.35 minutes, nearly twice as fast as the old estimate. Researchers combined optical observations from 2024 with reprocessed radar data from 1998 and discovered the asteroid is unusually bright with a high “albedo,” pointing toward an Xe-type composition. This means it reflects more sunlight than most small asteroids and may contain enstatite-rich material.
Researchers proved this by observing the asteroid during a rare close pass in 2024. They used the world’s biggest telescopes, including the Very Large Telescope and the Gran Telescopio Canarias. They created lightcurves showing changes in brightness as the asteroid rotated. Earlier studies only had limited angles, but the 2024 observations captured it from many directions, revealing the true shorter rotation period. Scientists then re-examined old radar data using the corrected spin rate and found the smaller size.
This discovery matters for several reasons. For the Hayabusa2 extended mission, a smaller and faster-spinning target means mission operations may be more challenging. Tools designed to fire projectiles or approach the surface may not work as planned. For planetary defense, understanding 1998 KY26 helps scientists model small, fast-spinning objects that could pose impact risks. Such objects are as large as the Tunguska and Chelyabinsk impactors.
Experts say these new results show how essential updated data is for mission planning. The research team notes that the asteroid’s weak structural strength, measured at less than 20 pascals, suggests it might be a loose rubble pile that somehow survives its fast spin. Others caution that it could still be a solid monolithic rock. The uncertainty adds tension, since future spacecraft operations must account for both possibilities.
This finding also links to larger scientific issues. Tiny, fast-rotating asteroids can teach scientists about how solar radiation, collisions, and heating change the orbits of near-Earth objects over time. Some researchers classified 1998 KY26 as a “dark comet” due to odd non-gravitational forces, but the new study finds no evidence of dust or gas, pushing scientists to rethink how these forces work.
What happens next depends on future observations. The asteroid will be too faint for ground-based study until Hayabusa2 arrives in 2031. The only chance to update measurements before then will come from the James Webb Space Telescope, which may observe the asteroid during two short visibility windows between 2028 and 2029. These data could confirm the new size and help determine its thermal properties.
This discovery shows how much scientists can learn from rare close passes. It also highlights how much uncertainty remains about small asteroids that could someday threaten Earth. The new study gives mission planners better tools, but it also leaves important questions open until Hayabusa2 reaches the asteroid.
Story Source:
Materials provided by Insert Institution Here. Content may be edited for style and length.
Journal Reference:
T. Santana-Ros, P. Bartczak, K. Muinonen, A. Rożek, T. Müller, M. Hirabayashi, D. Farnocchia, M. Micheli, R. E. Cannon, M. Brozović, O. Hainaut, D. Oszkiewicz, A. K. Virkki, L. A. M. Benner, A. Campo Bagatin, P. G. Benavidez, A. Cabrera-Lavers, C. E. Martínez-Vázquez, K. Vivas. Hayabusa2 extended mission target asteroid 1998 KY26 is smaller and rotating faster than previously known. Nature Communications, 2025. DOI: 10.1038/s41467-025-63697-4