标题： 小天体表面风化层长期运动趋势 显示英文标题

标题： Long-term Trends of Regolith Movement on the Surface of Small Bodies

摘要： 本文从非线性动力学的角度研究了太阳系小天体表面扰动风化层物质的长期迁移。我们提出了一种近似模型来描述长期质量运动，该模型结合了复杂的地形和不规则的引力场。以小行星101955贝努为代表，考察了动力环境的全局变化，这为旋转加速的小行星划分了蠕动-滑动-剥落区域。在蠕动区域，基于“触发-滑动”运动模式假设，建立了扰动风化层颗粒的动力学方程。计算了系统的平衡点、局部流形和大规模轨迹，以阐明长期风化层运动的动力学特性。通常，我们发现对于低自转速率，表面风化层颗粒从极地/赤道地区流向中纬度地区，这主要由地球位势梯度主导。而当自转加速到高速率时，风化层颗粒倾向于向赤道迁移，这与低纬度地区的局部平衡拓扑结构变化同时发生。从长期角度来看，我们发现平衡点主导着风化层运动的全局趋势。利用本文发展出的方法论，我们在自转加速过程中展望或回顾了风化层物质的长期运动，结果揭示了平衡点具有显著的调节作用。通过详细分析不同自转速率下的动力学方案，我们实现了对自转加速过程中风化层运动全局趋势的宏观预测，这解释了由风化层材料长期运动驱动的全球地质演化。 显示英文摘要

摘要： This paper studies the long-term migration of disturbed regolith materials on the surface of Solar System small bodies from the viewpoint of nonlinear dynamics. We propose an approximation model for secular mass movement, which combines the complex topography and irregular gravitational field. Choosing asteroid 101955 Bennu as a representative, the global change of the dynamical environment is examined, which presents a division of the creeping-sliding-shedding regions for a spun-up asteroid. In the creeping region, the dynamical equation of disturbed regolith grains is established based on the assumption of "trigger-slide" motion mode. The equilibrium points, local manifolds and large-scale trajectories of the system are calculated to clarify the dynamical characteristics of long-term regolith movement. Generally, we find for a low spin rate, the surface regolith grains flow toward the middle latitudes from the polar/equatorial regions, which is dominated by the gradient of the geopotential. While spun up to a high rate, regolith grains tend to migrate toward the equator, which happens in parallel with a topological shift of the local equilibria at low latitudes. From a long-term perspective, we find the equilibrium points dominate the global trends of regolith movements. Using the methodology developed in this paper, we give a prospect or retrospect to the secular motion of regolith materials during the spin-up process, and the results reveal a significant regulatory role of the equilibria. Through a detailed look at the dynamical scheme under different spin rates, we achieve a macro forecast of the global trends of regolith motion during the spin-up process, which explains the global geologic evolution driven by the long-term movements of regolith materials.