Formation of Microspherules of Lunar Regolith in Plasma–Dust Processes Initiated by Meteoroid Impacts

The possibility of the formation of microspherules in plasma-dust processes initiated by meteoroids impacting the lunar surface is discussed. It is demonstrated that spherules are formed from the material of the melt zone created by a high-speed meteoroid impacting the lunar surface. Initially, they rise above the surface of the Moon and then fall back. It is these spherules that were found in the course of investigation of the lunar soil. Liquid spherules solidify while floating above the surface of the Moon and acquire electric charges as a result of the interaction with electrons and ions, together with the solar radiation, thereby becoming part of the plasma-dust system above the Moon. The concentration of spherules in dusty plasma above the lunar surface and their size distribution are obtained. The upper bound of the spherule size in the distribution is determined by the existence of the upper bound in the statistical data on the size of relatively small meteoroids and amounts to several micrometers. The size of spherules substantially larger than 1 μm corresponds to meteoroids larger than 1 cm. It is impossible to obtain unique statistics with respect to size for large meteoroids. Therefore, it is possible to obtain the size distribution only of spherules of micron and submicron size. The size of meteoroids impacting the lunar surface and creating relatively large spherules can only be estimated. It is demonstrated that the presence of spherules in dusty plasma above the lunar surface can be discovered by piezoelectric sensors during future Luna-25 and Luna-27 missions.