Characteristics of dust plasma environment at lunar south pole

Abstract

Unlike the Earth, the Moon lacks the protection of an atmosphere and a global magnetic field, and is directly exposed to complex radiation environments such as high-energy cosmic rays, solar wind, and the Earth's magnetotail plasma. The surface of the Moon is covered with a thick layer of lunar soil, of which particles with a size of 30nm-20<i>μ</i>m are called lunar dust. In complex environments such as solar wind or magnetotail plasma, lunar dust carries an electric charge and becomes charged lunar dust. Charged lunar dust is prone to migration under the action of the electric field on the lunar surface. Charged migrated lunar dust is easy to adhere to the surface of instruments and equipment, causing visual impairment, astronauts' movement disorders, equipment mechanical blockage, sealing failure, and material wear, which affects the lunar exploration mission. As an important lunar exploration landing site, the lunar South Pole receives special solar radiation and produces a special dust plasma environment due to its special location. In order to provide an environmental reference for lunar South Pole exploration, it is necessary to explore the characteristics of the dust plasma environment in the lunar South Pole and its impact. In view of the lunar South Pole environment, this paper uses the Spacecraft Plasma Interactions Software(SPIS) software developed by the European Space Agency to model and simulate. The simulation obtains the logarithmic distribution of the lunar dust space density within the range of 0-200 m at the lunar South Pole, the potential distribution near the lunar surface, and the spatial distribution characteristics of plasma electrons and ions. The obtained lunar dust space density and lunar surface potential are similar to the previous theoretical derivation and field detection data, so the simulation results have high reliability. The spatial potential distribution and the spatial density distribution of electrons and ions in the lunar environment with and without lunar dust are compared. Finally, the following conclusions can be drawn: The research results show that the space potential increases with increasing altitude. The potential at 0-10 m near the South Pole of the Moon is about -40 V, and the space potential at 100 m is about -20 V. The density of lunar dust in the altitude range below 10 m is 10<sup>7.22</sup> m<sup>-3</sup>-10<sup>4.66</sup> m<sup>-3</sup>. The electron density in the dust plasma near the lunar surface is 10<sup>5.47</sup> m<sup>-3</sup>, and the ion density is 10<sup>6.07</sup> m<sup>-3</sup>, and both increase with increasing altitude. Charged lunar dust affects the spatial distribution of lunar dust, mainly by affecting the distribution of the space electric field, which leads to differences in electron distribution, but has little effect on ions.