Three-dimensional simulation of surface charging in meteorite craters on rotating asteroids

Meteorite craters on the asteroid surface obstruct the horizontal flow of solar wind, forming a plasma wake that modulates the particle fluxes and the electrostatic environment far downstream. In this study, the surface charging properties of asteroids with nontrivial terrain are simulated on the basis of the neural network and the finite element method. Key factors such as the location, size and depth-to-width ratio of craters are all considered. Under normal conditions, as the latitude of the crater increases, the potential variation at its floor during a rotation gradually becomes smoother, finally stabilizing around -27.5 V with minor fluctuations when the crater approaches the poles. Because of the diverging motions of electrons and the less deflected trajectories of ions, near the terminator, the surface potential variation within craters with low depth-to-width ratios primarily depends on ion density, which decreases with increasing depth. In contrast, for craters with a depth-to-width ratio greater than 0.5, the potential differences at the crater floor arise mainly from the electron distribution. While the surface potential appears indifferent to changes in crater size, only during solar storms, the floor of large-scale craters, such as those with a diameter of 800 m, perform a 26.78 V decrease in potential compared to small craters of 50 m. Both studies of localized plasma flow field and the surface charging phenomenon of asteroids have substantial influence on the future safe landing and exploration missions.