The Non-Principal-Axis Rotation and Convex Shape Model of Earth Quasi-Satellite and the Target of China's Tianwen-2 Mission (469219) Kamo`oalewa
Abstract
(469219) Kamo`oalewa is the most stable Earth quasi-satellite and the target of China's Tianwen-2 asteroid sample return mission. Due to its small size, fast rotation, and the limited observing geometry accessible from the ground, many physical properties of Kamo`oalewa remain poorly constrained, including the rotational state and shape. We obtained three epochs of high-cadence, high signal-to-noise photometric lightcurves of Kamo`oalewa with the Gemini North Telescope from 2026 April to May, supplemented by one lightcurve from the Lowell Discovery Telescope in 2026 May. Our analysis suggests that Kamo`oalewa is in a non-principal-axis rotation with an elongated shape. Four possible solutions exist, including a long-axis mode (LAM) solution and a short-axis mode (SAM) solution, as well as their corresponding mirrored angular momentum directions. The most preferable solution has a LAM model with a precession period Pϕ=27.65±0.03 min and a rotational period Pψ=50.49±0.08 min, and the angular momentum points to ecliptic coordinates (λ, β) = (226o±20o, −39o±20o), although we cannot rule out other solutions or other close-by periods due to aliasing. We also derived a convex shape inversion for the LAM models with consistent rotational parameters but could not find a satisfactory inversion for the SAM models. The corresponding angular momentum points to (λ, β)=(225o, −43o), and the periods are Pϕ=27.90 min and Pψ=49.66 min. The non-principal-axis rotation provides additional constraints on the dynamic history or the internal structure of Kamo`oalewa.
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BibTeX
@misc{sun2026nonprincipalaxis,
title = {{The Non-Principal-Axis Rotation and Convex Shape Model of Earth Quasi-Satellite and the Target of China's Tianwen-2 Mission (469219) Kamo`oalewa}},
author = {Xiaoyu Sun and Zhijun Song and Hanjie Tan and Bin Yang and Josef Ďurech and Nicholas Moskovitz and Audrey Thirouin and Samantha Hemmelgarn and Wen Bo and Yang Yu and Jian-Yang Li},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2608.00424},
eprint = {2608.00424},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.00424},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - The Non-Principal-Axis Rotation and Convex Shape Model of Earth Quasi-Satellite and the Target of China's Tianwen-2 Mission (469219) Kamo`oalewa
AU - Xiaoyu Sun
AU - Zhijun Song
AU - Hanjie Tan
AU - Bin Yang
AU - Josef Ďurech
AU - Nicholas Moskovitz
AU - Audrey Thirouin
AU - Samantha Hemmelgarn
AU - Wen Bo
AU - Yang Yu
AU - Jian-Yang Li
PY - 2026
DA - 2026/09/11
PB - arXiv
DO - 10.48550/arxiv.2608.00424
UR - https://arxiv.org/abs/2608.00424
AB - (469219) Kamo`oalewa is the most stable Earth quasi-satellite and the target of China's Tianwen-2 asteroid sample return mission. Due to its small size, fast rotation, and the limited observing geometry accessible from the ground, many physical properties of Kamo`oalewa remain poorly constrained, including the rotational state and shape. We obtained three epochs of high-cadence, high signal-to-noise photometric lightcurves of Kamo`oalewa with the Gemini North Telescope from 2026 April to May, supplemented by one lightcurve from the Lowell Discovery Telescope in 2026 May. Our analysis suggests that Kamo`oalewa is in a non-principal-axis rotation with an elongated shape. Four possible solutions exist, including a long-axis mode (LAM) solution and a short-axis mode (SAM) solution, as well as their corresponding mirrored angular momentum directions. The most preferable solution has a LAM model with a precession period P_ϕ=27.65±0.03 min and a rotational period P_ψ=50.49±0.08 min, and the angular momentum points to ecliptic coordinates (λ, β) = (226^o±20^o, −39^o±20o), although we cannot rule out other solutions or other close-by periods due to aliasing. We also derived a convex shape inversion for the LAM models with consistent rotational parameters but could not find a satisfactory inversion for the SAM models. The corresponding angular momentum points to (λ, β)=(225^o, −43^o), and the periods are P_ϕ=27.90 min and P_ψ=49.66 min. The non-principal-axis rotation provides additional constraints on the dynamic history or the internal structure of Kamo`oalewa.
ER -