Astronomers have discovered that asteroid 1998 KY26, the target of Japan's Hayabusa2 extended mission, is only 11 meters across and rotates every five minutes, far smaller and quicker than previously estimated. These findings, based on observations from major telescopes including ESO's Very Large Telescope, complicate the 2031 spacecraft encounter but boost scientific intrigue. The asteroid's tiny size marks it as the smallest ever targeted by a space mission.
Recent coordinated observations from observatories across continents, including the European Southern Observatory's Very Large Telescope in Chile's Atacama Desert, have provided fresh insights into asteroid 1998 KY26. Led by astronomer Toni Santana-Ros from the University of Alicante in Spain, the team combined these results with prior radar data to reveal the asteroid's true dimensions and spin rate. Previously thought to be about 30 meters wide with a 10-minute rotation, it is now confirmed at just 11 meters—small enough to fit inside the VLT's dome—and spinning twice as fast, completing a turn in roughly five minutes.
"We found that the reality of the object is completely different from what it was previously described as," Santana-Ros stated in the study published in Nature Communications. This asteroid is the final destination for JAXA's Hayabusa2 spacecraft, which successfully explored the much larger 900-meter asteroid Ryugu in 2018 and returned samples to Earth in 2020. With fuel to spare, Hayabusa2's extended mission will arrive at 1998 KY26 in 2031, making it the first spacecraft to visit such a diminutive body.
The updates pose challenges for the mission, particularly for any planned touchdown on the surface. "The smaller size and faster rotation now measured will make Hayabusa2's visit even more interesting, but also even more challenging," noted co-author Olivier Hainaut from ESO in Germany. The asteroid's bright surface suggests it is likely a solid rock fragment, possibly from a shattered larger body, though it could be a rubble pile. "We have never seen a ten-meter-size asteroid in situ, so we don't really know what to expect and how it will look," Santana-Ros added.
These observations enhance preparations for the encounter and have broader implications. Santana-Ros highlighted that the techniques used could aid future asteroid exploration, mining efforts, and defense against small near-Earth objects, similar to the 2013 Chelyabinsk meteor, which was slightly larger than 1998 KY26. Hainaut emphasized the ability to characterize such tiny potential hazards from Earth.