Surface Thermal Inertia of Near-Earth Asteroid (469219) Kamo`oalewa: Statistical Estimation and Implications

Abstract

The Chinese small body exploration mission Tianwen-2 is aimed at sampling the near-Earth, fast-rotating asteroid (469219) Kamo`oalewa and returning the samples to Earth. Characterisation of the currently unknown physical properties of Kamo`oalewa in the pre-mission phase would support mission implementation. In this study, we preliminarily estimate the surface thermal inertia of Kamo`oalewa using a statistical method, based on the Yarkovsky-related orbital drift of (–6.155 ± 1.758) × 10<sup>-3</sup> au/Myr for Kamo`oalewa obtained in our previous work. A reasonable estimate of the surface thermal inertia obtained is \(402.05_{{ - 194.37}}^{{ + 376.29}}\) J K^–1 m^–2 s^–1/2. This low value suggests the presence of coarse regolith on the surface of Kamo`oalewa or its nature as a porous rock. The regolith potentially present on the surface of Kamo`oalewa may have millimetre- to decimetre-sized grains with cohesive strengths varying from ~0.76 to ~0.045 Pa. If Kamo`oalewa is a porous rock, its porosity is expected to range from ~20 to 50%, corresponding to tensile strengths of ~1.3 to 11.5 MPa. This study provides preliminary insights into the surface thermal inertia of Kamo`oalewa from a statistical viewpoint, which may facilitate the Tianwen-2 mission.