太阳系中旋转小行星表面充电特性  

Surface charging characteristics of rotating asteroids in the solar system

作　　者：宋智颖 全荣辉[1] 刘志贵 Song Zhi-Ying;Quan Rong-Hui;Liu Zhi-Gui(College of Astronautics,Nanjing University of Aeronautics and Astronautics,Nanjing 210016,China)

机构地区：[1]南京航空航天大学航天学院,南京210016

出　　处：《物理学报》2024年第24期262-272,共11页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:42241148,51877111)资助的课题.

摘　　要：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1 h的-4.96 V降低为周期为七天的-5.97 V,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0.001 V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,so far,the influence of asteroid rotation on surface charging and the surrounding plasma has not yet been 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 establish a multi-scale model based on neural networks and the finite element method,thereby improving simulation efficiency and enabling three-dimensional dynamic simulations of rotating asteroids.Simulation results for asteroids with different rotation periods indicate that both the maximum surface potential and the minimum surface potential decrease as the rotation period increases.The minimum potential on the nightside decreases from-4.96 V with one-hour period to-5.97 V with one-week period.For asteroids with longer periods,this downward trend slows down:the period increases from one week to half a year,resulting in a potential change of 0.001 V.Because strong electric field near the the terminator accelerates electrons and ions,electrons respond more promptly to the electric field,owing to their much higher mobility and diffusion coefficient,exhibiting a more severe accumulation phenomenon than ions,resulting in the decrease of 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.When the period exceeds one week,this downward trend becomes less pronounced,specifically,the asteroid and plasma have enough time to reach equilibrium at various angles.During the passage of solar storms,there is a significant change in surface potential at different stages,with potential difference caused by rotation periods reaching hundreds of volts.Surface minerals also play a role,with plagioclase

关 键 词：小行星 太阳风等离子体 神经网络 表面充电 

分 类 号：P18[天文地球—天文学]