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26DUSTY PLASMAS AT THE MOON: RECENT DEVELOPMENTS AND
UNSOLVED PROBLEMS
S.I. Popel, A.P. Golub', G.G. Dolnikov, A.Yu. Dubinskii, Yu.N. Izvekova, S.I. Kopnin, A.V. Zakharov, L.M. Zelenyi
Space Research Institute RAS, Moscow, Russia
The future Russian lunar missions Luna 25 and Luna 27 are planned to be equipped with instruments for direct detection of nano- and microscale dust particles and determination of plasma properties over the surface of the Moon. Lunar dust over the Moon is usually considered as a part of a dusty plasma system. Here, we present the main our theory results concerning the lunar dusty plasmas. We start with the description of the observational data on dust particles on and over the surface of the Moon. We show that the size distribution of dust on the lunar surface is in a good agreement with the Kolmogorov distribution, which is the size distribution of particles in the case of multiple crushing. We discuss the role of adhesion which has been identified as a significant force in the dust particle launching process. We evaluate the adhesive force for lunar dust particles with taking into account the roughness and adsorbed molecular layers. We show that dust particle launching can be explained if the dust particles rise at a height of about dozens of nanometers owing to some processes. This is enough for the particles to acquire charges sufficient for the dominance of the electrostatic force over the gravitational and adhesive forces. The reasons for the separation of the dust particles from the surface of the Moon are, in particular, their heating by solar radiation and cooling. We consider migration of free protons in regolith from the viewpoint of the photoemission properties of the lunar soil. Finally, we develop a model of dusty plasma system over the Moon and show that it includes charged dust, photoelectrons, and electrons and ions of the solar wind. We determine the distributions of the photoelectrons and find the characteristics of the dust which rise over the lunar regolith. We show that there are no significant constraints on the Moon landing sites for future lunar missions that will study dusty plasmas in the surface layer of the Moon. We discuss also waves in dusty plasmas over the lunar surface. Furthermore, we formulate new problems concerning the dusty plasma over the lunar surface.
This work was supported by the RFBR (project no. 15-02-05627).
