In a cosmic twist, astronomers using some of the world’s most powerful telescopes have discovered that asteroid 1998 KY26, Japan’s Hayabusa2 space target, is far smaller and faster than anyone expected. The new data, gathered by observatories including Gemini South, SOAR, and the Víctor M. Blanco 4-meter Telescope, reveals that the asteroid is just 11 meters wide and spins at dizzying speed: one full rotation every five minutes.
“We found that the reality of the object is completely different from what it was previously described as,” says astronomer Toni Santana-Ros of the University of Alicante, Spain. “One day on this asteroid lasts only five minutes!”
Earlier estimates pegged the asteroid at 30 meters wide, rotating every 10 minutes. This updated profile means Japan’s Hayabusa2 spacecraft will face a much trickier landing when it reaches the asteroid in 2031.
Hayabusa2, operated by the Japanese Aerospace eXploration Agency (JAXA), is on an extended mission after successfully returning samples from the much larger asteroid Ryugu in 2020. With fuel to spare, the spacecraft is now headed toward 1998 KY26 to explore one of the smallest asteroids ever visited.
Asteroid Ryugu began its cosmic journey more than 4 billion years ago
“This will be the first time a space mission encounters a tiny asteroid,” notes the team. Previous missions have only studied space rocks hundreds or thousands of meters across.
To prepare for this unprecedented encounter, Santana-Ros and his team waited for 1998 KY26 to swing close to Earth. Because the asteroid is so small and faint, they needed massive telescopes to get a good look. Instruments like Gemini South (the only one to use multiple filters), SOAR, and the NSF Víctor M. Blanco Telescope played key roles in capturing the asteroid’s details. Gemini South, part of the International Gemini Observatory, is funded in part by the U.S. National Science Foundation and operated by NSF NOIRLab.
The observations revealed a bright surface, suggesting the asteroid might be a solid chunk of rock, possibly a fragment from a planet or another asteroid. Still, the team can’t rule out the possibility that it’s a loose pile of rubble held together by gravity.
“We have never seen a ten-meter-sized asteroid in situ, so we don’t really know what to expect and how it will look,” says Santana-Ros, who is also affiliated with the University of Barcelona.
And here’s the kicker: “The amazing story here is that the size of the asteroid is comparable to the size of the spacecraft that is going to visit it!” Santana-Ros adds. “And we were able to characterize such a small object using our telescopes, which means that we can do it for other objects in the future.”
This breakthrough could reshape how scientists plan future asteroid missions, and even open doors to asteroid mining.
As Santana-Ros puts it: “Our methods could have an impact on the plans for future near-Earth asteroid exploration or even asteroid mining.”
Journal Reference:
- Santana-Ros, T., Bartczak, P., Muinonen, K. et al. Hayabusa2 extended mission target asteroid 1998 KY26 is smaller and rotating faster than previously known. Nat Commun 16, 8275 (2025). DOI: 10.1038/s41467-025-63697-4