Free Astronomy Magazine November-December 2025

10 NOVEMBER-DECEMBER 2025 ASTRO PUBLISHING Because the asteroid is very small and, hence, very faint, studying it required waiting for a close en- counter with Earth and using large telescopes, like ESO’s VLT in Chile’s Ata- cama Desert. The observa- tions revealed that the asteroid has a bright sur- face and likely consists of a solid chunk of rock, which may have originated from a piece of a planet or an- other asteroid. However, the team could not com- pletely rule out the possi- bility that the asteroid is made up of rubble piles loosely sticking together. “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,” says San- tana-Ros, who is also affili- ated with the University of Barcelona. “The amazing story here is that we found that the size of the asteroid is comparable to the size of the spacecraft that is going to visit it! And we were able to characterise such a small object using our telescopes, which means that we can do it for other objects in the future,” says Santana-Ros. “Our methods could have an impact on the plans for future near-Earth asteroid exploration or even aster- oid mining.” “Moreover, we now know we can char- acterise even the smallest hazardous asteroids that could impact Earth, such as the one that hit near Chelyabinsk, in Russia in 2013, which was barely larger than KY 26 ,” concludes Hainaut. ! T his animation shows the touchdown manoeuvre that Japan’s Hayabusa2 spacecraft is likely to perform when it reaches its target in 2031, in a brief encounter with the asteroid 1998 KY 26 . Now that a new study has shown that this asteroid is roughly three times smaller than previously expected, and spinning twice as fast, this procedure may be more difficult to conduct. [ESO/M. Kornmesser. Asteroid: T. Santana-Ros et al. Hayabusa2 model: SuperTKG (CC-BY-SA)] A t only 11 metres across, the asteroid 1998 KY 26 is the smallest asteroid that any space mission has attemp- ted to touch down on. In 2031, Japan’s Hayabusa2 space- craft is planned to rendezvous with this tiny asteroid, after its prior successful mission to the much larger 162173 Ryugu in 2018. Ryugu is 900 metres wide and can be seen in this video looming behind 1998 KY 26 , although in real- ity both asteroids follow very different orbits, and are only shown close together in this animation for compari- son While both asteroids are spinning, 1998 KY 26 spins much more quickly, further complicating Hayabusa2’s fu- ture touchdown. [ESO/M. Kornmesser. Asteroid models: T. Santana-Ros, JAXA/University of Aizu/Kobe University] H ere we have a size comparison between the previous tar- get asteroid for Japan’s Hayabusa2 space mission, 162173 Ryugu, and 1998 KY 26 . Hayabusa2 collected samples from Ryugu in 2018, returning them to Earth in 2020. After this suc- cessful mission, 1998 KY 26 was chosen as Hayabusa2’s next target. Now, a new study with ESO’s Very Large Telescope (VLT) has shown that this asteroid is only 11 metres wide, making it a much more difficult asteroid to touch down on than previously thought. This artist’s impression highlights the sheer size difference between Hayabusa2’s targets. [ESO/ M. Kornmesser. Asteroid models: T. Santana-Ros, JAXA/Uni- versity of Aizu/Kobe University] teroid — all previous missions visited asteroids with di- ameters in the hundreds or even thousands of metres. Santana-Ros and his team observed 1998 KY 26 from the ground to support the preparation of the mission.