New Observations Reveal Asteroid Is Smaller and Faster Than Expected
“The reality of this object is completely different from what previous studies suggested,” says Toni Santana-Ros, an astronomer at the University of Alicante in Spain and lead author of the Nature Communications paper. By combining newly collected data with earlier radar observations, the team determined that the asteroid measures just 11 meters across—small enough to fit inside the dome of the Very Large Telescope (VLT) unit used for the study. They also found that the asteroid rotates once every five minutes, far faster than the earlier estimates of a roughly 30-meter diameter and a ten-minute rotation period.
A Smaller, Faster Target Creates New Challenges for Hayabusa2
“The reduced size and rapid spin rate will make Hayabusa2’s rendezvous even more fascinating, but also significantly more challenging,” notes co-author Olivier Hainaut of the European Southern Observatory (ESO) in Germany. The asteroid’s tiny dimensions and swift rotation complicate any attempt to carry out a brief surface touchdown—a maneuver the mission team had originally planned for.
Asteroid 1998 KY26 is the final destination of the Japan Aerospace Exploration Agency’s (JAXA) Hayabusa2 spacecraft. During its primary mission, Hayabusa2 visited the 900-meter-wide asteroid Ryugu in 2018 and successfully returned samples to Earth in 2020. Thanks to surplus fuel, the spacecraft was assigned an extended mission that will conclude in 2031, when it is scheduled to encounter 1998 KY26. This flyby will mark the first time a spacecraft has visited an asteroid of such small size; all previous missions have targeted bodies hundreds or thousands of meters across.
Ground-Based Telescopes Provide Rare Insights Into a Tiny Object
To support mission planning, Santana-Ros and his colleagues observed 1998 KY26 from Earth. Because the asteroid is both faint and extremely small, they had to wait for a relatively close approach to Earth and then rely on some of the world’s most powerful telescopes, including ESO’s VLT in Chile’s Atacama Desert.
The observations suggest that the asteroid has a bright surface and is likely a solid, rocky fragment—possibly originating from a shattered planetesimal or larger asteroid. However, the team cannot fully rule out the possibility that it may instead be a loosely bound cluster of debris. “We have never seen an asteroid only ten meters in size up close, so we truly do not know what to expect,” says Santana-Ros, who is also affiliated with the University of Barcelona.
Implications for Future Exploration and Planetary Defense
“What’s remarkable is that the asteroid is roughly the same size as the spacecraft that will visit it,” Santana-Ros emphasizes. “And the fact that we could characterize such a tiny object from Earth means we can apply these techniques to many others.” According to the team, this approach could influence future plans for near-Earth asteroid missions or even early-stage concepts for asteroid mining.
“Importantly, we now know that we can study even the smallest potentially hazardous asteroids—like the one that exploded over Chelyabinsk in 2013, which was only slightly larger than KY26,” adds Hainaut.
These findings are presented in the paper “Hayabusa2♯ mission target 1998 KY26 preview: decametre size, high albedo and rotating twice as fast” published in Nature Communications.
