The exosphere of Mercury, which has much in common with the exosphere of the Moon, can also contain suspended dust particles, which, under the action of intense solar radiation, acquire positive charges and form one of the components of the dusty plasma system. In addition to dust particles, there are photoelectrons above the planet surface, formed as a result of interaction of solar radiation with the planet surface, as well as with suspended dust particles. Mercury, unlike the Moon, has its own magnetosphere, which affects the parameters of dusty plasma system. The dusty plasma parameters near the Mercury surface can vary depending on the distance from the planet to the Sun, which considerably changes when the planet moves along the elongated orbit, and also depending on the localization of the region under consideration on the planet surface. Thus, near the magnetic poles, the solar wind can reach the planet surface, which must be taken into account when determining the plasma parameters. Far from the magnetic poles, the effect of the solar wind can be neglected. In the dusty plasma near the surface of Mercury, one can expect the development of linear and nonlinear wave processes. In this paper, nonlinear waves are considered, namely, dust acoustic solitons and nonlinear periodic waves. The profiles of potentials of high-amplitude solitons and nonlinear periodic waves are obtained, as well as the soliton amplitudes as functions of the altitude above the planet surface and soliton velocity.

Wave processes in dusty plasma near the surface of Mercury are discussed. The near-surface layers of Mercury's exosphere have a number of common features with those of the exosphere of the Moon, e.g., there are dust particles above the illuminated side of both cosmic bodies that become positively charged due to the photoelectric effect. Mercury has its own magnetosphere that protects the surface from particles of the solar wind. However, the solar wind can reach the surface of the planet near the magnetic poles. Therefore, dust particles of the same size get different charges depending on their localization above the Mercury's surface. A drift wave turbulence can appear in dusty plasma in the magnetic field near the Mercury's surface in the presence of gradient of electron concentration. The solar wind that streams at speeds of about 400 km/s relative to plasma near the surface of the planet can induce longitudinal electrostatic oscillations with frequencies determined by the electron plasma frequency. We analyze wave processes taking into account the difference in parameters at aphelion and perihelion of the Mercury's orbit, along with the fact whether the dust particles are located near the magnetic poles or far from them.

The circumlunar environment is a dusty plasma consisting of small particles of lunar regolith, photoelectrons, electrons, and solar wind ions. When moving around the Earth, part of the trajectory of the Moon passes through the Earth's magnetosphere. In addition, the magnetic field is characteristic for some areas on the Moon, the so-called lunar magnetic anomalies. The magnetic field values above these areas can exceed the magnetic field values of the Earth's magnetosphere in the region of the Moon's trajectory by one or two orders of magnitude. The magnetic field and photoelectron density gradients can lead to the development of drift turbulence. The relevant conditions are discussed in this work.

The possible effect is studied of the magnetic field of Earth's magnetotail and the magnetic field in the regions of magnetic anomalies of the Moon on the processes of formation of dusty plasma above the Moon. It is shown that due to the action of the magnetic field in Earth's magnetotail, transfer of charged dust is possible over long distances above Moon's surface. Accordingly, the dusty plasma above the surface of the Moon illuminated by the solar radiation can exist in the entire range of lunar latitudes. The transfer of dust grains over long distances due to the uncompensated magnetic component of Lorenz force is a new qualitative effect that is absent in the absence of magnetic field. The magnetic component of Lorenz force acting on the dust grain from the fields of magnetic anomalies is either lower or comparable to the similar force calculated for the magnetic fields of Earth's magnetotail. However, due to the substantial localization of magnetic anomalies, their effect on the dynamics of charged dust grains above the Moon's surface does not lead to new qualitative effects.

The program of scientific research of the Luna-25 lunar lander includes the experiment Dust monitoring of the Moon (in Russian, Pylevoi monitoring Luny (PmL)), which provides for the study of the dynamics of lunar microparticles and parameters of the near-surface dusty plasma. Using the PmL instrument, it is planned to record for a long time individual microparticles above the lunar surface, to measure and evaluate their physical characteristics (momentum, velocity, charge, mass, and concentration), as well as to monitor the dynamics of the parameters of the near-surface dusty plasma environment (density, temperature, and potential). The instrument has passed successfully the entire range of ground tests.

In 2022, our country will return to the Moon. This is a daunting task with many challenges and dangers. One of them, so far the least studied and most obscure, is the subject of this article, prepared using the materials of the report Exploration of the Moon and Planets with the Help of Automatic Spacecraft: A Prelude to the Exploration of the Moon by Man (it was heard at a scientific session of the General Meeting of RAS members on April 21, 2021). The surface of the Moon, like most atmosphereless bodies, is covered with a layer of dust: a fine fraction of regolith, crushed over hundreds of millions of years of being on the surface of the planet. Under the influence of external factors-both natural and anthropogenic-dust particles can rise from the surface, levitate under the influence of electrostatic forces, and settle on spacecraft. The experience of the six American Apollo manned missions showed that lunar dust microparticles affected the service systems of the lander, deposited on the astronauts' suits, got into the air recirculation systems of the sealed lander and, as a result, influenced the health of the astronauts. Considering the size of such particles, which can be tens or hundreds of nanometers, it has become clear that the toxicity of moondust is one of the most serious problems in the study of the Moon with human participation. This conclusion was made at the end of the Apollo program. The factor of lunar dust during manned missions to the Moon is discussed, and methods for solving this problem are outlined.

We demonstrate the possibility of the existence and propagation of dust acoustic solitons in the dusty plasma of the lunar exosphere, which contains, in addition to electrons and ions of the solar wind and photoelectrons from its surface, charged dust particles, as well as photoelectrons emitting from the surfaces of these particles. Soliton solutions are found and the ranges of possible velocities and amplitudes of such solitons are determined depending on the height above the lunar surface for different subsolar angles.

The surface of the Moon, like that of any airless body in the Solar System, constantly experiences micrometeorite bombardment as well as the influence of solar radiation, solar wind, and other factors of outer space. As a result of the impacts of high-velocity micrometeorites over billions of years, the lunar surface silicate basis crumbles, turning into particles with a wide size distribution. Considering the explosive nature of their origin, these particles are characterized by an extremely irregular shape with sharp edges or conglomerates sintered at high temperatures or almost spherical droplets. On the illuminated side of the Moon, solar radiation, especially the ultraviolet part of its spectrum, and solar wind streams interact with the upper regolith layer, charging the regolith surface. The photoelectrons generated above the surface create, together with the charged regolith surface, a near-surface double layer. The electric field generated in this layer, as well as the particle charge fluctuations on the surface, create conditions under which electric forces may exceed the gravitational force and the van der Waals force of adhesion. As a result, micron- and submicron-sized regolith particles become capable of detaching from the surface and levitating above it. These dynamic processes cause the transport of dust particles above the lunar surface and the scattering of sunlight on these particles. Glows of this kind were observed over the lunar surface by television systems of American and Soviet landing vehicles in the early stages of lunar exploration. American astronauts who landed on the lunar surface during the Apollo program also discovered manifestations of lunar dust. It turns out that dust particles levitating over the regolith surface due to natural processes and those took off the surface due to anthropogenic factors cause many technological problems that compromise the performance of landing vehicles and their systems, hamper astronaut activity on the lunar surface, and are detrimental to their health. Based on the results of these missions, it is concluded that micron- and submicron-sized dust particles, levitating above the surface, pose a major, barely surmountable obstacle in further research and exploration of the Moon. Since then, studies of physical processes associated with the behavior of lunar dust, manifestations of its aggressive properties (toxicity), and ways to reduce the harmful effects of dust on engineering systems and on humans have become topical in theoretical and experimental research. In this review, the results of the past half century of studies on the behavior of dust particles serve as a basis to discuss the formation of the lunar regolith and the Moon's near-surface plasma-dust exosphere under the influence of outer space factors. The causes and conditions underling the behavior of dust particles are examined as well as implications of these processes, the influence of anthropogenic factors, and possible hazards to spacecraft and engineering systems during the implementation of the currently planned programs of lunar research and exploration. The main unsolved problems are listed in studying the behavior of the dust component of the lunar regolith; ways to address the problematic issues are discussed.

A renaissance is being observed currently in investigations of the Moon. The Luna-25 and Luna-27 missions are being prepared in Russia. At the same time, in connection with the future lunar missions, theory investigations of dust and dusty plasmas at the Moon are being carried out by scientists of the Space Research Institute of the Russian Academy of Sciences. Here, the corresponding results are reviewed briefly. We present the main theory results of these investigations concerning the lunar dusty plasmas. We show, in particular, the absence of the dead zone near a lunar latitude of 80 where, as was assumed earlier, dust particles cannot rise over the surface of the Moon. This indicates that there are no significant constraints on the Moon landing sites for future lunar missions that will study dust in the surface layer of the Moon. We demonstrate that the electrostatically ejected dust population can exist in the near-surface layer over the Moon while the dust appearing in the lunar exosphere owing to impacts of meteoroids present everywhere. The calculated values of number densities at high altitudes of the particles formed as a result of the impacts of meteoroids with the lunar surface are in accordance (up to an order of magnitude) with the data obtained by the recent NASA mission LADEE. Finally, we formulate new problems concerning the dusty plasma over the lunar surface.

Physical conditions in the near-surface layer of the Moon are overviewed. This medium is formed in the course of the permanent micrometeoroid bombardment of the lunar regolith and due to the exposure of the regolith to solar radiation and high-energy charged particles of solar and galactic origin. During a considerable part of a lunar day (more than 20%), the Moon is passing through the Earth's magnetosphere, where the conditions strongly differ from those in the interplanetary space. The external effects on the lunar regolith form the plasma-dusty medium above the lunar surface, the so-called lunar exosphere, whose characteristic altitude may reach several tens of kilometers. Observations of the near-surface dusty exosphere were carried out with the TV cameras onboard the landers Surveyor 5, 6, and 7 (1967-1968) and with the astrophotometer of Lunokhod-2 (1973). Their results showed that the near-surface layer glows above the sunlit surface of the Moon. This was interpreted as the scattering of solar light by dust particles. Direct detection of particles on the lunar surface was made by the Lunar Ejects and Meteorite (LEAM) instrument deployed by the Apollo 17 astronauts. Recently, the investigations of dust particles were performed by the Lunar Atmosphere and Dust Environment Explorer (LADEE) instrument at an altitude of several tens of kilometers. These observations urged forward the development of theoretical models for the lunar exosphere formation, and these models are being continuously improved. However, to date, many issues related to the dynamics of dust and the near-surface electric fields remain unresolved. Further investigations of the lunar exosphere are planned to be performed onboard the Russian landers Luna-Glob and Luna-Resurs.