Surface dynamics of small fast-rotating asteroids: Analysis of possible regolith on asteroid 2016 HO3

The Chinese Tianwen-2 mission is planned to explore and sample the near-Earth asteroid 2016 HO3, also named 469219 Kamo-oalewa. This paper intends to answer the question of whether 2016 HO3 has any regolith. A 3D model of an irregular shape was reconstructed from light curve data of 2016 HO3, with simulated impact craters embedded on its surface. We used numerical simulations to calculate the acceleration from gravity, fast rotation, and the van der Waals cohesive force. We found that the poles have a higher chance of hosting regolith, and the regolith may also rest on the walls of craters that face toward the rotation axis, making them potential sample collection sites. On the surface of 2016 HO3, the van der Waals force is strong enough to hold particles smaller than several centimeters against centrifugal force. Furthermore, we compare a pair of transient processes: thermal fatigue, which generates small particles, and micro-impacts, which remove the surface mass. Thermal fatigue is at least comparable to, and perhaps more efficient than, micro-impacts for 2016 HO3. Therefore, it is highly possible that regolith exists on the surface of 2016 HO3.