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HSE researchers, together with colleagues from Space Research Institute of RAS, MIPT, and the University of Colorado, ventured to find out where the plasma-dust cloud around the Moon comes from. To do this, they compared theoretical calculations with experimental data and theorized that this cloud likely consists of matter that rose from the Moon’s surface as a result of meteoroid collisions. Their paper determines the nature of the dusty plasmas found around the Moon and provides a theoretical foundation for previous observations.
The interplanetary space in the Solar System is filled with dust particles. They are present in planet ionospheres and magnetosphere plasmas, as well as circulate cosmic bodies that lack an atmosphere. Due to high temperatures, the only place where there is no dust is on the Sun and in near proximity to it.
‘During the Surveyor and Apollo space missions to the Moon, it was observed that sunlight scatters at the terminator, which leads to lunar horizon glowand streamers over the surface (despite the Moon’s lack of atmosphere). Most probably, the light scatters on charged dust particles, the source of which is the Moon’s own surface. Indirect proof of the existence of a lunar plasma-dust cloud was also observed during Soviet expeditions, Luna 19 and Luna 22, according to Sergey Popel, one of authors of the research project, Doctor of Science in Physics and Mathematics, Professor at the HSE Faculty of Physics and Head of the Laboratory of Plasma Dust Processes in Space Objects at Space Research Institute of RAS.
The project’s authors looked at the possibility of the lunar plasma-dust cloud’s evolution due to meteoroid collisions with the Moon’s surface. The data received on the basis of this theory generally coincides with the results of experimental studies carried under the auspices of the American LADEE (Lunar Atmosphere and Dust Environment Explorer) mission.
A cloud of submicron dust surrounds the Moon within a radius of several hundred kilometers. The dust parameters were measured by using a LDEX shock ionization sensor, which directly detects dust particles when a space vehicle is conducting orbit. The aim of the experiment was to detect the distribution of dust particles by altitudes, sizes and concentrations above various sections of the lunar surface. The data received from the LADEE experiment proved to be an incentive for continuing the theoretical studies previously commenced by the IKI researchers. The experts received an opportunity to compare their calculations with the experimental data. It turns out that they comply, particularly in terms of the particles’ speed and concentration.
‘The concentration of plasma-dust cloud particles in our calculations doesn’t contradict with the experimental data. A constant flow of meteoroids of micron, millimeter sizes hits the lunar surface. Therefore, matter is, in fact, constantly thrown from the surface, and part of it is actually melted. Liquid melted drops rise above the lunar surface and then harden. By interacting with solar wind electrons and ions, as well as solar radiation, they get electric charges. Some of the particles depart from the Moon and fly off into space. And the particles that “lacked the speed” compose the plasma dust cloud over the lunar surface.’ Sergey Popel explained.
The LADEE experiments revealed a stepwise rise in dust concentration during interactions of annual meteor showers with the Moon. In turn, this effect was particularly evident during Geminids (high-speed meteor showers). Furthermore, this confirms the link between the dust cloud’s evolution and meteoroid collisions with the lunar surface. Theories that sate that dust particles rise over the Moon surface due to electrostatic processes, such as the so-called ‘fountain model’, nevertheless cannot explain the occurrence of dust rising to high altitudes and, consequently, the evolution of plasma-dust clouds observed through the LADEE project.
The authors added that further studies are necessary: as of now, they have presented a simple model, which requires further development. For instance, it’s possible to carry out calculations while giving due consideration to the factors of surface geometry.
IQ