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Published June 2025 | Version Published
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Keck and Gemini Characterization of Hayabusa2# Rendezvous Target 1998 KY₂₆

Creators

  • 1. ROR icon Eureka Scientific
  • 2. ROR icon California Institute of Technology
  • 3. ROR icon Observatoire de la Côte d'Azur
  • 4. ROR icon University of Tokyo
  • 5. ROR icon University of Leicester
  • 6. ROR icon University of Hawaii at Manoa
  • 7. ROR icon Space Telescope Science Institute
  • 8. ROR icon Griffith Observatory
  • 9. ROR icon Goddard Space Flight Center
  • 10. ROR icon Gemini North Observatory

Abstract

Near-Earth object (NEO) 1998 KY26 is a target of the Hayabusa2# spacecraft, which it will rendezvous with in 2031 July. The asteroid has been noted to rotate rapidly and has a large out-of-plane nongravitational acceleration. We present observations consisting of deep-g- and R-band imaging obtained with the Keck I/Low Resolution Imaging Spectrometer (LRIS) and visible spectroscopy from Gemini North/Gemini Multi-Object Spectrograph (GMOS) taken of 1998 KY26 on 2024 June 8–9 when the asteroid was ∼0.037 au from the Earth. The asteroid does not show evidence of a dust coma and has a surface brightness profile similar to nearby background stars in the deep images. The spectrum of 1998 KY26 from the combined LRIS and GMOS observations most closely resembles Xe-type asteroids, possessing a spectral slope of 6.71% ± 0.43% 100 nm−1, and color indices g – r = 0.63 ± 0.03, r – i = 0.15 ± 0.03, i – z = 0.05 ± 0.04, and implies a diameter of ∼10 m. From our deep image stacks, we compute a 3σ upper limit on the dust production of 1998 KY26 of <10−5 kg s−1, <10−2 kg s−1, and <10−1 kg s−1 assuming μm, mm, and cm size dust particles. In addition, we compare the orbit of 1998 KY26 and other known asteroids with large nongravitational parameters to NEO population models and find that the majority, including 1998 KY26, likely originated from the inner Main Belt, while the second most numerous group originates from the outer main belt, followed by a third group possibly originating from the Jupiter Family Comet population. Given its inner Main Belt origin, its Xe-type spectrum, and rapid rotation, we hypothesize that the nongravitational acceleration of 1998 KY26 may be caused by the shedding of large dust grains from its surface due to its rotation rather than H2O vapor outgassing.

Copyright and License

© 2025. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

The authors wish to thank Alessandro Morbidelli for his help with computing the NEO source probabilities for the objects studied in this manuscript, and Josh Walawender for supporting the Keck/LRIS observations. The authors also wish to thank the Gemini North operations staff for help coordinating the observations described in this manuscript.

Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c)3 nonprofit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Based on observations obtained at the international Gemini Observatory, a program of NSF NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the U.S. National Science Foundation on behalf of the Gemini Observatory partnership: the U.S. National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnologìa e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea).

Keck and Gemini North Observatory is located on Maunakea, land of the Kānaka Maoli people, and a mountain of considerable cultural, natural, and ecological significance to the indigenous Hawaiian people. The authors wish to acknowledge the importance and reverence of Maunakea and express gratitude for the opportunity to conduct observations from the mountain.

Facilities: Keck:I - KECK I Telescope (LRIS), Gemini:Gillett - .

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Dates

Available
2025-05-12
Published online

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Caltech groups
Palomar Observatory, Division of Physics, Mathematics and Astronomy (PMA), Division of Geological and Planetary Sciences (GPS)
Publication Status
Published