image: The tiny asteroid 1998 KY26 (center) is observed here by the Gemini South telescope, one half of the International Gemini Observatory, funded in part by the U.S. National Science Foundation and operated by NSF NOIRLab. The observations have revealed that 1998 KY26 is just 11 meters wide, almost three times smaller than previously thought, and is spinning once every 5 minutes, which is almost two times faster than expected. This image is composed of exposures taken through four filters. As exposures are taken, the asteroid remains fixed in the center of the telescope’s field of view. However, the positions of the background stars change relative to the asteroid, causing them to appear as colorful streaks in the final image.
Credit: International Gemini Observatory/NOIRLab/NSF/AURA/T. Santana-Ros
Astronomers using observatories around the world, including the Gemini South telescope, the SOAR telescope and the Víctor M. Blanco 4-meter Telescope funded in part by the U.S. National Science Foundation and operated by NSF NOIRLab, have found that the asteroid 1998 KY26 is almost three times smaller and spinning much faster than previously thought. The asteroid is the 2031 target for Japan’s Hayabusa2 extended mission, and the new observations offer key information for the mission’s operations.
“We found that the reality of the object is completely different from what it was previously described as,” says astronomer Toni Santana-Ros, a researcher from the University of Alicante, Spain. The new observations, combined with previous radar data, have revealed that the asteroid, 1998 KY26, is just 11 meters wide. It is also spinning about twice as fast as previously thought: “One day on this asteroid lasts only five minutes!" he says. Previous data indicated that the asteroid was around 30 meters in diameter and completed a rotation in approximately 10 minutes. The smaller size and faster rotation will make the spacecraft’s touchdown maneuver more difficult to perform than anticipated.
1998 KY26 is set to be the final target asteroid for the Japanese Aerospace eXploration Agency (JAXA)’s Hayabusa2 spacecraft. In its original mission, Hayabusa2 explored the 900-meter-diameter asteroid 162173 Ryugu in 2018, returning asteroid samples to Earth in 2020. With fuel remaining, the spacecraft was sent on an extended mission until 2031, when it’s set to encounter 1998 KY26, aiming to learn more about the smallest asteroids. This will be the first time a space mission encounters a tiny asteroid — all previous missions visited asteroids with diameters in the hundreds or even thousands of meters.
Santana-Ros and his team observed 1998 KY26 from the ground [1] to support the preparation of the mission. Because the asteroid is very small and, hence, very faint, studying it required waiting for a close encounter with Earth and the use of large telescopes, like Gemini South, SOAR, the NSF Víctor M. Blanco Telescope and European Southern Observatory's Very Large Telescope. Gemini was the only telescope observing the object through multiple filters, which proved crucial for its characterization. Gemini South is one half of the International Gemini Observatory, funded in part by the U.S. National Science Foundation (NSF) and operated by NSF NOIRLab.
The observations revealed that the asteroid has a bright surface and likely consists of a solid chunk of rock, which may have originated from a piece of a planet or another asteroid. However, the team could not completely rule out the possibility that the asteroid is composed of rubble piles loosely sticking together. “We have never seen a ten-meter-sized asteroid in situ, so we don't really know what to expect and how it will look,” says Santana-Ros, who is also affiliated with the University of Barcelona.
“The amazing story here is 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 characterize 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 asteroid mining.”
Notes
[1] The telescopes include Gemini South with the Gemini Multi-Object Spectrograph (GMOS), Southern Astrophysical Research (SOAR) Telescope, the NSF Víctor M. Blanco Telescope with the Dark Energy Camera (DECam), European Southern Observatory's Very Large Telescope (VLT) with FOcal Reducer and low dispersion Spectrograph 2 (FORS2), and Gran Telescopio CANARIAS (GTC) with the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) instrument.
More information
This research was presented in a paper titled “Hayabusa2 extended mission target asteroid 1998 KY26 is smaller and rotating faster than previously known” to appear in Nature Communications (doi: 10.1038/s41467-025-63697-4).
The team is composed of T. Santana-Ros (Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, and Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (IEEC-UB), Spain), P. Bartczak (Instituto Universitario de Física Aplicada a las Ciencias y a las Tecnologías, Universidad de Alicante, Spain and Astronomical Observatory Institute, Faculty of Physics and Astronomy, A. Mickiewicz University, Poland [AOI AMU]), K. Muinonen (Department of Physics, University of Helsinki, Finland [Physics UH]), A. Rożek (Institute for Astronomy, University of Edinburgh, Royal Observatory Edinburgh, UK [IfA UoE]), T. Müller (Max-Planck-Institut für extraterrestrische Physik, Germany), M. Hirabayashi (Georgia Institute of Technology, United States), D. Farnocchia (Jet Propulsion Laboratory, California Institute of Technology, USA [JPL]), D. Oszkiewicz (AOI AMU), M. Micheli (ESA ESRIN / PDO / NEO Coordination Centre, Italy), R. E. Cannon (IfA UoE), M. Brozovic (JPL), O. Hainaut (European Southern Observatory, Germany), A. K. Virkki [Physics UH], L. A. M. Benner (JPL), A. Cabrera-Lavers (GRANTECAN and Instituto de Astrofísica de Canarias, Spain), C. E. Martínez-Vázquez (International Gemini Observatory/NSF NOIRLab, USA), K. Vivas (Cerro Tololo Inter-American Observatory/NSF NOIRLab, Chile).
NSF NOIRLab, the U.S. National Science Foundation center for ground-based optical-infrared astronomy, operates the International Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), NSF Kitt Peak National Observatory (KPNO), NSF Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and NSF–DOE Vera C. Rubin Observatory (in cooperation with DOE’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona.
The scientific community is honored to have the opportunity to conduct astronomical research on I’oligam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence of I’oligam Du’ag to the Tohono O’odham Nation, and Maunakea to the Kanaka Maoli (Native Hawaiians) community.
Links
- Read the paper: https://www.nature.com/articles/s41467-025-63697-4
- ESO press release
- Check out other NOIRLab Science Releases
Contacts
Lars Lindberg Christensen
Head of Communications, Education & Engagement
NSF NOIRLab
Email: lars.christensen@noirlab.edu
Journal
Nature Communications
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
Hayabusa2 extended mission target asteroid 1998 KY26 is smaller and rotating faster than previously known
Article Publication Date
18-Sep-2025