Journal Article

Shape, Regolith Size and Thickness, SMFe0 Content, and Spectral Type of Tianwen-2 Target Asteroid (469219) Kamo‘oalewa

Lin, Honglei, Zhang, Xiaoping, Zhang, Guozheng, Zhang, Yongxiong, Vernazza, Pierre, Cloutis, Edward, Fenucci, Marco, Zhao, Jin, Niu, Yunbo, Zhang, Pengfei, Yan, Xiaoran, Li, Yang, Wu, Xing, Wang, Xiaobin, Lu, Xuejin

2026

Overview

China’s Tianwen-2 spacecraft was launched on 2025 May 29 and will arrive at the Earth quasi-satellite (469219) Kamo‘oalewa in 2026 July. We previously reported that Kamo‘oalewa develops an LL-chondrite-compositional, highly space-weathered surface. Here, using the light-curve data and the Cellinoid model, we modeled Kamo‘oalewa’s shape, rotation period, and pole orientation. We then estimated the global distribution of regolith critical size using the balance method of gravity, cohesive force, and centrifugal force. Furthermore, in the temperature range of 253.15−473.15 K, we measured the thermal parameters of laser-irradiated LL chondrite powder that best matches Kamo‘oalewa’s spectrum, estimating Kamo‘oalewa’s thermal inertia and skin depth (lower limit of regolith thickness). Using the radiative transfer mixing model, we also estimated the sub-micrometer-sized iron (SMFe0) content in Kamo‘oalewa’s regolith. Finally, using the MIT online spectral classification tool for the laser-irradiated LL chondrite powder, we obtained a virtual spectral type of Kamo‘oalewa. Our model gives a size of 68 × 46 × 39 m, a rotation period of 27.66 minutes, and a pole orientation of 134 .° 7 longitude and −11 .° 4 latitude for Kamo‘oalewa. Regolith grains with a size <2 cm can remain stable over 93.8% of the global surface area of Kamo‘oalewa. Laser-irradiated LL chondrite powder shows a low thermal inertia (163.14−232.31 J m−2 K−1 s−1/2), corresponding to a thermal skin depth of 3.1−3.5 mm on Kamo‘oalewa. An SMFe0 content of 0.29 ± 0.05 wt.% is required to match Kamo‘oalewa’s spectrum. The virtual spectral type of Kamo‘oalewa is given as “Sqw.”

• Publisher: IOP Publishing
• Subject: Asteroids / Centrifugal force / Chinese spacecraft / Chondrites / Lasers / Near-Earth Objects / Radiative transfer / Regolith / Rotation / Space weathering / Spacecraft / Specific heat / Spectral classification / Thermal inertia / Thermodynamic properties / Thickness