The next leg of Japan’s Hayabusa2 mission is now facing an unexpected challenge: the asteroid it is targeting for its next visit, 1998 KY26, has turned out to be significantly smaller and rotating much faster than previously suspected, adding a new layer of difficulty to the project.
Data from multiple observatories reveal the asteroid is only one-third of its expected size and has twice the presumed rotational speed, but still, the Japan Aerospace Exploration Agency (JAXA) will have six years to adjust its Hayabusa2 mission, currently planned for a 2031 meet-up with 1998 KY26.
The European Southern Observatory’s Very Large Telescope (ESO’s VLT) in Chile was a major data source for the new research, revealed in a new paper published in Nature Communications.
Hayabusa2 Surprise
“We found that the reality of the object is completely different from what it was previously described as,” said lead author Toni Santana-Ros, a researcher from the University of Alicante, Spain, who led the team in support of JAXA’s mission.
The target now stands revealed as a mere 11 meters wide and completes a rotation in just five minutes based on radar data. This means that the asteroid is even smaller than the dome on the telescope used to observe it, the VLT. Earlier estimates clocked the rotation at 10 minutes and measured a 30-meter diameter.
“The smaller size and faster rotation now measured will make Hayabusa2’s visit even more interesting, but also even more challenging,” says co-author Olivier Hainaut, an astronomer at ESO in Germany.
With a smaller and faster target, the touchdown mission has now become significantly more of a technical challenge than it already was for Hayabusa2’s final objective.
A Success So Far
Despite the new difficulties, Hayabusa 2 has already been a tremendous success, returning samples from the asteroid 162173 Ryugu in 2020, collected during a 2018 surface touchdown. Scientists have prized those samples that have already led to many interesting discoveries, including a significant reconsideration of how space rocks brought water to the early Earth.
With that achievement behind it, the spacecraft still has enough fuel to extend its mission for a 2031 rendezvous with 1998 KY26. Never before has such a tiny asteroid been investigated up close. Ryugu is about 900 meters in diameter, and the Bennu asteroid visited by NASA’s OSIRIS-Rex mission is roughly 500 meters in diameter.
While the observations have led the team to draw some conclusions about the nature of 1998 KY26, there remain two possibilities. The asteroid’s surface is quite bright, and Santana-Rios suggests it is likely one solid piece of rock, broken off from a planet or a larger asteroid. Alternatively, the asteroid may consist of smaller rubble piles, only loosely attached to form a whole, the asteroid’s small size adding to the uncertainty.
Understanding Asteroids
“We have never seen a ten-metre-[sized] asteroid in situ, so we don’t really know what to expect and how it will look,” said Santana-Ros.
Beyond supporting the Hayabusa2 mission, the new work is a benchmark for ground-based asteroid studies. This is the first time researchers have resolved an object so small that it is comparable in size to the spacecraft going to visit it. The techniques utilized here will be of use to future work investigating the near-Earth environment, asteroid mining, and even planetary defense.
While sending a reconnaissance vehicle is the most comprehensive way to analyze an asteroid, future impact events may not come with enough warning time to plan and launch such a mission. Refining ground-based observations to better understand such objects may be crucial to future deflection missions, mitigating the risk of future potentially devastating impact events comparable to the famous 1908 Tunguska event.
The paper, “Hayabusa2 Extended Mission Target Asteroid 1998 KY26 is Smaller and Rotating Faster than Previously Known,” appeared in Nature Communications on September 18, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.