Keck and Gemini Characterization of Hayabusa2# Rendezvous Target 1998 KY26

Abstract

Near-Earth object (NEO) 1998 KY _26 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 KY _26 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 KY _26 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 3 σ upper limit on the dust production of 1998 KY _26 of <10 ^−5 kg s ^−1 , <10 ^−2 kg s ^−1 , and <10 ^−1 kg s ^−1 assuming μ m, mm, and cm size dust particles. In addition, we compare the orbit of 1998 KY _26 and other known asteroids with large nongravitational parameters to NEO population models and find that the majority, including 1998 KY _26 , 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 KY _26 may be caused by the shedding of large dust grains from its surface due to its rotation rather than H _2 O vapor outgassing.

Keywords

• Near-Earth objects
• Asteroid surfaces