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空间等离子体环境中的带电粒子附着和运动会在小行星表面形成可观测的电位，这一表面充电现象阻碍了小行星的安全着陆和探索。传统方法计算速度较低，且聚焦于静态小行星，缺少对实际情况中旋转小行星的充电机制研究。为此，本文提出了基于神经网络和有限元法的多尺度模型，实现了对旋转小行星的三维动态模拟。对小行星和周围环境的模拟和分析结果表明，小行星表面的最大和最小电位均会随着自转周期增长而减小，夜侧最小电位由周期为一小时的-4.96V降低为周期为七天的-5.97V，当周期长于七天时，这种下降趋势变缓，七天到半年的周期增长仅能造成0.001V的电位变化。太阳风暴经过期间，电子和离子的密度及温度升高，自转周期导致的电位差异可达上百伏。表面材料的组成也会影响小行星表面电位受周期影响的差异程度。由斜长石或斜方辉石构成时，不同自转周期小行星之间的表面电位差异较为明显，而钛铁矿构成的小行星则更依赖于所处姿态。研究自转小行星的表面充电现象，对探究小行星与太阳风相互作用的性质至关重要。The attachment and movement of charged particles in the space plasma environment can result in observable potentials on the asteroid surface, this surface charging phenomenon has been extensively studied. However, the influence of asteroid's rotation on surface charging and the surrounding plasma is not yet fully understood. Traditional methods using numerical integration and PIC have slow computation speeds, and mainly focus on the charging mechanisms of static asteroids. In this study, we established a multi-scale model based on neural networks and the finite element method, improving simulation efficiency and enabling three-dimensional dynamic simulations of rotating asteroids. Simulation results for asteroids with different rotation periods indicate that the maximum and minimum surface potentials decrease as the rotation period increases. The minimum potential on the nightside decreases from -4.96V with one-hour period to -5.97V with one-week period. For asteroids with longer periods, this decreasing trend slows down, with the increase from one week to half a year causing changes of 0.001V in potential. Because strong electric field near the the terminator accelerates electrons and ions, electrons respond more promptly to the electric field because of their much higher mobility and diffusion coefficient, exhibiting a more severe accumulation phenomenon than ions, then decrease the surface potential. This phenomenon is most pronounced when the solar wind is obliquely incident, where the subsolar point is close to the terminator, resulting in the strongest electric field. This downward trend becomes more when the period exceeds one week, specifically, the asteroid and plasma have enough time to reach equilibrium at all angles. During the passage of solar storms, the surface potentials at different stages vary significantly, with potential differences caused by rotation periods reaching hundreds of volts. Surface minerals also play a role, plagioclase is the most sensitive mineral among those explored, while ilmenite appears indifferent to changes in rotation periods. Understanding the surface charging of asteroids under various rotation periods and angles is crucial for further research on solar wind plasma and asteroid's surface dust motion, providing a reference for the safe landing and exploration of asteroids.
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Keywords:
- Asteroids /
- Solar wind plasma /
- Neural networks /
- Surface charing
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