Scientists at St Petersburg University and Moscow State Technical University of Civil Aviation have developed a new more effective investigation technique to study the lunar soil without having to land on the Moon. The method is based on the research findings that were carried out by scientists during the Soviet period and have been forgotten for almost 40 years. The research findings are published in the world’s leading journal Planetary and Space Science.

The lunar exploration techniques at distance from the Moon are not a new phenomenon. Until recently, the elemental composition of lunar rocks was studied using so-called passive techniques of remote analysis based on the spectrometry of gamma, neutron, and X-ray radiation excited in the surface layer of lunar rocks by various sources of natural origin and detected onboard a lunar orbiter. And although the passive techniques have helped to achieve significant success in the study of lunar rocks, they all have significant drawbacks.

The main disadvantage of the passive techniques is the low intensity flows of natural characteristic radiations of lunar rocks. Humans are far from being able to increase their intensity, not to mention to control these radiation flows. Advancing these techniques is also a hard nut to crack. We cannot increase spatial resolution of the obtained results, i.e lunar rocks composition maps, or increase the number of elements we should detect, or increase accuracy of detecting the elemental composition of the materials. For example, the most popular technique – X-ray fluorescence analysis – depends on solar flares. They last for a very short time, and it is possible to predict them only for three days

Only active techniques to study lunar rocks elemental composition can lead us to a breakthrough in lunar exploration. They are based on spectrometry of artificially induced characteristic radiations of rock forming elements of lunar rocks.

Evgeny Kolesnikov, an author of the research project, Doctor of Physics and Mathematics, Professor in the Department of Physical Mechanics at the Faculty of Mathematics and Mechanics at St Petersburg University

The scientist conducts various studies in this direction with his scientific group. His recent work has been published in collaboration with Aleksandr Zelensky, Candidate of Physics and Mathematics and Associate Professor in the Department of Electrical Engineering and Airborne Electrical Equipment at Moscow State Technical University of Civil Aviation. He was a post-graduate student at the Department of Physical Mechanics at St Petersburg University. ‘Today, what we have been researching into is becoming more and more popular due to a global surge in the interest to study the Earth’s natural satellite. ’Along with Russia and the United States, Europe, China, India and Japan are now participating in the work on studying the Moon. An important place in modern research, as in the past, belongs to the study of the elemental composition of the surface rocks of the Moon’, said Aleksandr Zelensky.

The technique developed by the scientists at St Petersburg University and Moscow State Technical University of Civil Aviation is based on the spectrometry of the characteristic X-ray radiation (CXR) of lunar rocks. The researchers propose to artificially excite this radiation in the surface layer of the Moon's soil with an electron beam: a special set of equipment creates a beam and directs it to the area of interest on the lunar surface, and then, based on the analysis of the recorded X-ray radiation, determines the elemental composition of the rocks of this area. As a result, detailed maps of the composition of the Moon's surface rocks can be quickly created.

The research will be carried out from a spacecraft orbiting the Moon at a distance of about 40 km.

The choice of the optimal type of characteristic radiation and the optimal method of its excitation is determined by the need to create a system that, on the one hand, would ensure the determination of the elemental composition of lunar rocks, and on the other hand would have the mass and dimensions that allow it to be placed in a low lunar orbit using existing space vehicles.

The technique developed by the scientists meet all these standards.

‘The main advantage of our technique over other active systems of elemental analysis at a distance is that we can obtain relatively low levels of energy of electrons in the probe beam by using the neutral hydrogen atom beams. The levels can vary from several dozens of keV (for the elements at the beginning of the periodic table) to hundreds of keV (for the elements in the middle of the periodic table). Moreover, due to the large CXR excitation cross-sections, it is possible to generate sufficiently intensive CXR fluxes in the satellite orbit given a relatively low current of the probing beam. The intensity of the CXR fluxes from the lunar rock elements is sufficient for their reliable detection against the background of the decelerating radiation flux excited simultaneously with the CXR and against the background of the natural X-ray flux in the circumlunar space,’ said Evgeny Kolesnikov.

This technique will allow us to obtain more detailed and accurate maps of the elemental composition of the lunar surface, including light elements (magnesium, aluminum, silicon) and heavy elements (calcium, titanium, iron). It will also enable us to determine how the lunar landforms depend on their elemental composition and what elements can be found in specific parts of the lunar surface that are of special interest to scientists.

A more effective study of the lunar surface is necessary not only to enrich our knowledge of its nature, but also-in the future-to build bases on the Moon and begin its industrial development.

Notably, Russian scientists started to study the possibilities for lunar surface investigations from the lunar orbit as long ago as 50 years. In 1960–1970, both the USSR and the USA gained considerable success in lunar investigations. In the USSR, the Research Institute of Mathematics and Mechanics at Leningrad University played a significant role in developing systems of distance exploration of lunar surface. Yet all research endeavours in lunar exploration came to an end in the 1980s, with many projects frozen and sent to the archives.

Today, advancing the techniques for lunar investigations is gaining popularity once again. The Earth’s satellite is in the focus of many nations, including Russia and the USA. What had been developed in 1970s–80s is further investigated by the scientists at St Petersburg University and Moscow State Technical University of Civil Aviation, said Evgeny Kolesnikov. What makes a difference is the new technologies that are used to bring to life these ideas. ‘New is a well forgotten past, especially in our case. In our research project, we use the advancements achieved by the Research Institute of Mathematics and Mechanics at the University during the Soviet period, including the manuscript that dates back to 1982 and was deposited at the All-Union Institute for Scientific and Technical Information (VINITI). It was written by me and Mr Kuryshev, who was a senior research associate at the Research Institute of Mathematics and Mechanics. In the manuscript, we proved for the first time that this technique could be successfully used in practice,’ said Evgeny Kolesnikov.