Asteroid target for Hayabusa2 found to be smaller and faster than expected

Asteroid target for Hayabusa2 found to be smaller and faster than expected
by Erica Marchand
Paris, France (SPX) Sep 22, 2025

Astronomers using the European Southern Observatory's Very Large Telescope and other facilities worldwide have discovered that asteroid 1998 KY26, the final target of Japan's Hayabusa2 mission, is significantly smaller and rotates much faster than earlier estimates suggested. The findings provide crucial guidance for mission planning as the spacecraft prepares for its 2031 rendezvous.

Lead researcher Toni Santana-Ros of the University of Alicante explained that their analysis shows the asteroid measures only 11 meters across, compared with previous estimates of about 30 meters. The team also found that KY26 completes a full rotation in just five minutes, roughly twice as fast as prior measurements indicated.

"The smaller size and faster rotation now measured will make Hayabusa2's visit even more interesting, but also even more challenging," said ESO astronomer Olivier Hainaut. He noted that a delicate touchdown maneuver could be more difficult to achieve under these conditions.

Hayabusa2, operated by the Japanese Aerospace Exploration Agency (JAXA), originally explored the 900-meter asteroid Ryugu in 2018 and returned samples to Earth in 2020. With resources still available, the mission was extended to visit KY26 in 2031. This will be the first spacecraft encounter with such a tiny asteroid, making it an unprecedented opportunity to study the smallest building blocks of the solar system.

Ground-based observations were essential to refining KY26's properties, as its faintness makes it visible only during close Earth flybys. Using ESO's Very Large Telescope in Chile, scientists confirmed the asteroid has a relatively bright surface and is likely composed of solid rock. However, they cannot fully rule out the possibility that it is a rubble pile loosely bound by gravity.

"We have never seen a ten-metre-size asteroid in situ, so we don't really know what to expect and how it will look," Santana-Ros remarked. He added that their ability to characterize such a small object demonstrates the potential for future studies of other near-Earth asteroids, including those of concern for planetary defense or possible resource use.

Hainaut emphasized the broader significance: "We now know we can characterise even the smallest hazardous asteroids that could impact Earth, such as the one that hit near Chelyabinsk in 2013, which was barely larger than KY26."

Research Report:Hayabusa2 extended mission target asteroid 1998 KY26 is smaller and rotating faster than previously known