YORP effect on the evolution of asteroid spin states

Abstract

With the rise of the second deep space exploration, more and more attention has been paid to the research of asteroid as well as the YORP effect. The YORP effect, mainly arising from the thermal re-radiation from an irregularly shaped surface, may cause significant changes in spin rate and obliquity of an asteroid over millions of years. The study of the YORP effect plays an essential role in understanding the evolution of asteroids, the formation of binary systems, and the origin and development of the solar system. There are several methods on the evaluation of the YORP effect based on different models in the existing literature. As applying basic research, this study reviews the theory of the YORP effect, including thermal physical model (TPM), and improves the derivation of the formula. Furthermore, a horizon map is considered to describe the self-shelter, and the magnitude and direction of the radiative recoil force are amended according to the local horizon map. Based on the polyhedral asteroid model, an algorithm is proposed to attain the horizon map, the relationship between the inclination of the asteroid rotation axis and the YORP moment, and to simulate the spin state evolution numerically. Comparisons on numerical calculations and astronomical observation analyses are performed for several simple conditions to validate the performance of the TPM algorithm. Then, using the precise polyhedral shape models derived from radar observations, the YORP moment of many asteroids and its rotation state evolution are investigated. This study will help to reveal the formation and evolution of different asteroid structures and is of considerable significance to the target selection and target physical properties characterization of future asteroid exploration missions.