Japan’s Hayabusa2 spacecraft, already renowned for its successful sample return from asteroid Ryugu in 2020, faces an unprecedented challenge in its extended mission. New astronomical observations have revealed that asteroid 1998 KY26, the target for Hayabusa2’s 2031 rendezvous, is far smaller and faster than previously believed. Initially thought to be about 30 metres wide and rotating once every 10 minutes, KY26 has now been found to measure just 11 metres across and spins once every five minutes. The findings were published on Thursday, following observations by the European Southern Observatory’s Very Large Telescope (VLT) in Chile.
“We found that the reality of the object is completely different from what it was previously described as,” said Toni Santana-Ros, astronomer at the University of Alicante and the University of Barcelona, who led the study using the VLT.
Challenges for Hayabusa2’s extended mission
Hayabusa2’s mission extension was approved after its return from Ryugu, allowing the spacecraft to continue towards KY26. While it has enough fuel to make the journey, the new revelations raise serious complications. The asteroid’s size is comparable to the spacecraft itself, complicating efforts to orbit and potentially land on its surface. Its rapid spin further intensifies the challenge, as completing one rotation in just five minutes makes maintaining proximity and stability extremely difficult.
Olivier Hainaut, astronomer at the European Southern Observatory, emphasised the complexity: “The smaller size and faster rotation now measured will make Hayabusa2’s visit even more interesting, but also even more challenging.”
This marks the first mission ever to attempt exploration of an asteroid this small, and the encounter will demand precision unlike any previous planetary mission. Astronomers had to wait until KY26’s close pass to Earth to refine their calculations, highlighting just how elusive such small space rocks are.
Scientific value and broader implications
Despite the technical hurdles, studying KY26 carries enormous scientific value. Its bright surface suggests it could be a solid monolithic rock, though it might also be a loosely bound rubble pile. Understanding such objects is crucial, not just for planetary science but also for planetary defence. Asteroids of similar size have struck Earth before, such as the Chelyabinsk event in 2013, which caused widespread damage and injuries.
As Santana-Ros explained, “We have never seen a 10-metre-size asteroid in situ, so we don’t really know what to expect and how it will look.” This mission could therefore provide vital insights into how small asteroids are structured and how they behave in space. Hayabusa2’s work at KY26 will also inform future missions involving asteroid mining and strategies to mitigate potential threats to Earth.
The Hayabusa2 mission is now poised to make history once again, this time by attempting to characterise the smallest asteroid ever targeted by a spacecraft. While the new findings make the mission more complex, they also promise to expand humanity’s understanding of small near-Earth objects.