Summary and Keywords
Since the early 1990s, in analytical reviews, experts have increasingly been paying attention to the growing scarcity of rare and rare earth metals (REM) necessary for the development of advanced technologies in modern industry. The volume of the world market has increased over the past 50 years from 5,000 to 125,000 tons per year, which is explained by the extensive use of REM in the rapidly developing areas of industry associated with the advancement of high technology. Unique properties of REM are primarily used in the aerospace and other industrial sectors of the economy, and therefore are strategic materials. For example, platinum is an indispensable element that is used as a catalyst for chemical reactions. No battery can do without platinum. If all the millions of vehicles traveling along our roads installed hybrid batteries, all platinum reserves on Earth would end in the next 15 years! Consumers are interested in six elements known as the platinum group of metals (PGM): iridium (Ir), osmium (Os), palladium (palladium, Pd), rhodium (rhodium, Rh), ruthenium (ruthenium, Ru), and platinum itself. These elements, rare on the Earth, possess unique chemical and physical properties, which makes them vital industrial materials. To solve this problem, projects were proposed for the utilization of the substance of asteroids approaching the Earth. According to modern estimates, the number of known asteroids approaching the Earth reaches more than 9,000. Despite the difficulties of seizing, transporting, and further developing such an object in space, this way of solving the problem seemed technologically feasible and cost-effectively justified. A 10 m iron-nickel asteroid could contain up to 75 tons of rare metals and REM, primarily PGM, equivalent to a commercial price of about $2.8 billion in 2016 prices.
However, the utilization of an asteroid substance entering the lunar surface can be technologically simpler and economically more cost-effective. Until now, it was believed that the lunar impact craters do not contain the rocks of the asteroids that formed them, since at high velocities the impactors evaporate during a collision with the lunar surface. According to the latest research, it turned out that at a fall rate of less than 12 km/s falling body (drummer) can partially survive in a mechanically fractured state. Consequently, the number of possible resources present on the lunar surface can be attributed to nickel, cobalt, platinum, and rare metals of asteroid origin. The calculations show that the total mass, for example, of platinum and platinoids on the lunar surface as a result of the fall of asteroids may amount more than 14 million tons. It should be noted that the world’s known reserves of platinum group metals on the Earth are about 80,000 tons.
Since the early 1990s, in analytical reviews, experts have increasingly been paying attention to the growing scarcity of rare and rare earth elements.
A study of the problems associated with the use of rare earth metals (REM) shows that over the last 50 years the demand for this resource has experienced a steady upward trend, which is explained by the widespread use of REM in fast-growing areas of industry associated with the advancement of high technologies. First of all, consumers are interested in six elements, known as the platinum group of metals (PGM): iridium (Ir), osmium (Os), palladium (palladium, Pd), rhodium (rhodium, Rh), ruthenium (ruthenium, Ru), and platinum itself. These elements, rare on the Earth, possess unique chemical and physical properties, which makes them vital industrial materials.
For example, the use and production of rare niobium (Nb) metal is rapidly increasing, due to a combination of its properties, such as refractoriness; the ability to form heat-resistant, superconducting, and other alloys; corrosion resistance; and so on. Niobium is widely used for the production of superconducting magnets and alloys with high heat resistance for jet aviation and rocket technology. Niobium also found its application in the production of containers for the storage of radioactive waste or installations for their use. Niobium increases the strength of metals such as titanium, molybdenum, and zirconium, and simultaneously increases their heat resistance. Niobium-containing alloys and pure niobium are used to make rocket parts and parts of the airborne equipment of Earth’s artificial satellites.
The increase in demand mentioned is superimposed on the ever decreasing rate of extraction of these resources. This unfavorable trend is further complicated by a number of geopolitical circumstances. The resources of rare and rare earth elements are very unevenly distributed. Thus, two deposits in South Africa provide 80% of the world’s platinum production. The greater part—92% of the niobium used in the world—is exported from Brazil.
Currently, almost all the reserves of rare earth elements—97%—are supplied by China. Pointing to such a disproportion, in 2010 year analysts of the world’s largest financial conglomerate, Goldman Sachs Group, Inc., noted that a measure of the growing deficit is, among other things, a sharp increase in world prices for rare metals and REM. At the time of the 2010 prices had risen almost tenfold from the level of 2009 and continued to grow. If in 2010 the cost of 1 kg of REM was $10.30, then during the next two years it went up to $162.66. However, according to forecasts of analysts from Goldman Sachs Group, Inc., the explored reserves, for example, platinum, copper, and nickel on Earth, would last no more than 40 years (Toor, 2011). Different sources forecast roughly the same timescale for the disappearance of most rare metals and REM on Earth. The current situation means researchers need to turn the search for REM resources toward the now accessible part of near-Earth space.
The idea that water-ice deposits exist in the permanently shadowed areas of lunar polar regions is heavily debated among scientists and is seen as an important component of extraterrestrial resources. These deposits could potentially be used for the production of rocket fuel and substances for ensuring human life on the Moon as the first stage of possible expansion in the future.
Since the 1980s have been marked by an increase of new information of evidence for cold-trapped volatiles at the lunar poles (Li et al., 2018).
Orbital measurements reveal an enhancement in hydrogen at both poles, which is interpreted as evidence for surface or subsurface water ice (Mitrofanov et al., 2010). In addition, recent Moon Mineralogy Mapper (M3) data reveal hydroxylation of the lunar surface (Wöhler et al., 2017). Lunar hydroxyl and water are targets of interest both as scientific repositories and for exploration purposes.
Resource Possibilities of Asteroids Close to the Earth
In its customer dispatch, Goldman Sachs gave a detailed analysis of the current situation and, in particular, called for the development of platinum mining in outer space (Saefong, 2015).
According to analysts at Goldman Sachs, at present there are no financial and technological barriers to the development of asteroid resources. According to the preliminary development of specialists in space technology from the California Institute of Technology, the creation of survey probes will cost several tens of millions of dollars. The machinery to catch near-Earth asteroids approaching the Earth will require expenditures of 2.6 billion dollars. Financial analysts believe that these investments are quite affordable for modern venture companies. After all, the construction of a single mine for the extraction of REM on Earth costs a billion dollars. At the same time, thanks to the development of private space companies, the cost of launches is constantly decreasing. If earlier in the era of space shuttles, sending into orbit one kilogram of cargo would cost $30,000, today these costs have already been reduced to $5,000. Private space companies SpaceX and Blue Origin promise to reduce these amounts by several times due to reuse of the first stages of rockets and other components. Thus, according to forecasts of Goldman Sachs analysts, the initial costs will quickly be paid off. In the development of an asteroid, a mining company can obtain platinum worth $50 billion.
The article (Diamandis & Anderson, 2012) cites data from another private company for the development of space resources—Planetary Resources, Inc. (PRI), according to which a metal asteroid comparable in size to a football field, as a rule, possesses reserves of platinum for the specified amount of money. PRI was one of the first to announce that the purpose of its creation is the utilization of material resources of near space (Edwards, 2017). The research of this company involves the creation of new space vehicles and a new technology for the utilization of asteroid resources.
The basic concept developed by PRI since 2012 is an orbital complex in the form of an elastic “bag” equipped with a propulsion system for maneuvering in space (see Figure 1; Diamandis & Anderson, 2012). It is assumed that the asteroid chosen in advance can be captured by this device and move to a stationary circumlunar orbit or to Lagrange points 1 or 2, where the object will stay for a long time and gradually undergo development. In the framework of the technology being developed, it is planned it will be used on asteroids that are in orbits with perihelion distances of less than or equal to 1.3 au. It is obvious that at the current capability level of rocket technology of disposal, asteroids of limited dimensions may be exposed. In this connection, the stage of initial search and selection of objects acquires special importance.
In the scheme developed by PRI, at the initial stage it is assumed that the choice of the desired object will be carried out on the basis of remote analysis, using ground-based or space-based telescopes.
In the initial steps to determine the goals and objectives of the new company, specialists from PRI calculated the possibilities of selecting objects using ground-based telescopic observations and the economic efficiency of further utilization of the resources of the selected asteroid.
Figure 2 shows the results of this analysis, published in the journal New Scientist (Clark, 2012). For marketing analysis, the results of telescopic observations of the asteroid 1986 DA, carried out by the famous researcher of the bodies of the solar system, W. Hartmann, were used in 1994. The left diagram in Figure 2 shows the chemical composition of this metal asteroid, measuring about 2 km and having a mass of 3 × 1013 kg. The main component of the asteroid is iron, with an admixture of platinum, nickel, and cobalt.
At the time of the research (1994), the world market situation was such that the total cost of the asteroid 1986 DA material, if it could be disposed of, could amount to 25 trillion dollars. But in a few years, at the time of the formation of PRI (2012), the situation on the world metal market had changed dramatically, and the total cost of the asteroid could have amounted to 87.2 trillion dollars. It should be noted that in the latter case, the greatest value was represented by nickel reserves, not platinum, as one would expect. For the sake of clarity of estimates, the authors of the study showed in the right diagram the amount of the U.S. public debt, at the time of the study, equal to 15 trillion dollars.
However, the first objects for development can be only asteroids with dimensions in the meter range, for the utilization of which see the scheme shown in Figure 1. Nevertheless, the specialists of PRI believe that in this case, the implementation of the project will be economically justified. As an example, data on typical compositions of asteroids of various types are given. It is known that a typical S-type asteroid (a stone asteroid) of about 10 meters in size can contain a metal fraction with a total mass of 650 tons, which includes about 50 kg of rare metals and REM. A more promising option is to dispose of the substance of an M-type asteroid (metallic asteroid) of the same size. To assess the economic feasibility of such an operation, one can use the data published in Shaw (2012), such an iron-nickel asteroid could contain up to 75 tons of rare metals and REM, primarily PGM, equivalent to a commercial price of about 8 billion dollars in market prices in 2016.
In connection with the foregoing, the problem of choosing an object for resource development becomes particularly important. Therefore, in the future, the management of PRI, for the analysis of closely approaching asteroids, plan to widely use orbital telescopes mounted on small satellites, weighing 30–50 kg, which obviously will lead to a reduction in the cost of the entire program.
The first devices of this type of “Arkyd” series have already been prepared for test in space. Figure 3 (on the sidebar) shows the general view of the small satellite “Arkyd” in the orbital configuration (Lewicki, Diamandis, & Anderson, 2015).
The first vehicle of this series, Arkyd-3, was delivered to the International Space Station by the SpaceX CRS-6 space-rocket complex on April 14, 2015. Three months later, the Arkyd-3 spacecraft was launched into the near-earth orbit via the International Space Station (ISS) lock device and launched a test flight of 90 days duration (Figure 3; Lewicki et al., 2015).
In November 2016, the government of Luxembourg became the minority shareholder of PRI (Lewicki & Schneider, 2016). According to the agreement, the European shareholder provides 25 million euros of financing for the launch of the Arkyd-6 satellite. The aim of this mission, launched in January 2018, is to study closely approaching asteroids potentially suitable for resource development.
In 2013, another private company appeared in the United States, which aimed to solve scientific and technological problems in the search for and utilization of natural resources on asteroids (Spector, 2013). In strategic terms, Deep Space Industries adopted a slightly different scheme of initial stages and further technological development. Since the main task was initially to study and develop resources on asteroids of considerable size, it is technologically not supposed to use the technique of catching and transporting objects using a “space bag.” In this regard, it is planned that the choice of potential targets be carried out by contact methods with the help of appropriate apparatuses (Brandt-Erichsen, 2016).
At the state level, at the request of the National Aeronautics and Space Administration (NASA), a number of research organizations, under the leadership of the Keck Institute for Space Studies, developed its own project to capture, transport, and dispose of a small asteroid (Brophy, Culick, & Friedman, 2012).
One version of a plan discussed by a group of scientists and engineers at the California Institute of Technology was dedicated to investigating the feasibility and requirements of capturing a near-Earth asteroid, bringing it closer to our planet, and using it as a base for future manned spaceflight missions. NASA estimates there are 19,500 asteroids of at least about 100 m wide, which are large enough to detect with telescopes within 45 million km of Earth.
Another project involves capturing an asteroid to put in a high orbit around the Moon.
Figure 4 provides a conceptual diagram of the system for asteroid capture considered in this project. It is assumed that the most rational solution to the problem will be the development of a small asteroid with a diameter of about 7 m. The planned dimensions of the container are 15 m in diameter and 10 m in length. Figure 5 provides a conceptual diagram of the moment of capture considered in this project.
It is assumed that long distances extended to a near-Earth orbit by an Atlas-5 carrier rocket when reaching a remote object will be overcome by low-thrust engines (ionic engines), while further maneuvering would be carried out with the aid of several xenon engines.
The Keck version of events would take six to ten years and would see a craft heading to the target asteroid and capturing it in a big bag before bringing it back to the Moon.
According to the schedule of the project, after being put into low Earth orbit in 2025, the device will take about four more years to find the chosen asteroid and to seize it. In the future, the device, along with the captured asteroid, must move to a high near-moon orbit, which will take another two to six years. According to preliminary calculations, the entire first stage of the project could last up to 10 years. By this time, the manned space complex should have been completed; using this, the development of the asteroid substance would have been carried out already with the participation of astronauts (Figure 6).
Resources on the Lunar Surface
Initially, the recognized direction was the study and possible utilization of the resources of asteroids. According to the majority of expert opinions, such a decision was considered technologically and economically quite effective, despite the obvious complications of operations for capturing and transporting objects for further development. These features are evident in the analysis of all the details described in the project “NASA–Keck ISS.” But simultaneously with these works, the results of new studies that allow us to consider an alternative way of mining rare metals and REM in near-Earth space began to appear. It has been confirmed that the asteroid substance, as an unquestionable source of such resources, is in sufficient quantities on the lunar surface, which allows its utilization by technologically more simple methods.
The results of the first studies of lunar material samples, delivered to the Earth, really showed that the surface layer of the Moon in the mass is intensely enriched with a meteorite substance. It was found that the pure metallic iron found in the lunar rocks is likely to have an extra-lunar meteorite origin and can serve as an indicator of the introduced substance. According to preliminary results, based on the data on the chemical analysis of samples delivered to the Earth by the Apollo and Luna missions, the admixture of meteoritic matter in the surface layer of the Moon was estimated at a value of approximately 1–2% by different researchers. In the course of subsequent studies, these data were refined.
Among the samples of the lunar substance brought to Earth by the “Apollo 12” crew was a fragment of breccia, which has a number of exotic properties (Andersen & Hinthorne, 1972). Sample 12013, of about 5 cm in size, had a mass of 82.3 g (see Figure 7) (Quick, James, & Albee, 1981a). As a result of a detailed analysis of the chemical composition of this fragment, it was found out that in addition to typical elements for the lunar material, the following components were found: barium (Ba)—up to 2 wt. %, niobium (Nb)—up to 2 wt. %, zirconium (Zr)—up to 2,200 ppm, chromium (Cr)—up to 2,300 ppm, germanium (Ge)—up to 500 ppm. These are included in the rare Earth category (according to the classification of the lunar rocks—KREEP rocks, (an acronym built from the letters K (the atomic symbol for potassium), REE (rare-earth elements) and P (for phosphorus)). The presence of such inclusions is virtually unambiguous evidence of the introduction of asteroid components into the lunar material. In addition, studies based on isotope analysis have shown that sample 12013 consists of an extremely complex mixture of melts and other components of undetermined origin (Quick, James, & Albee, 1981b).
In this case, despite the fact that the sample was found in the Oceanus Procellarum, the substance of marine basalt in this breccia is absent. The repeated determination of the age of individual components showed that the youngest components date back to 4.16–4.17 billion years ago, and older fragments are approaching the age of the original lunar differentiation—about 4.5 billion years ago.
The age of marine basalts of the Oceanus Procellarum is on average 3.1–3.3 billion years in many definitions. Thus, the researchers came to the unanimous opinion that during its formation the studied sample underwent shock metamorphism about 4 billion years ago in the era of intense bombardment of the Moon by meteorites and asteroids. In the Oceanus Procellarum, this fragment of breccia was apparently abandoned from the highland during a later shock event.
Returning to the chemical composition of sample 12013, attention should be paid to the relatively high content of rare niobium metal, the unique properties of which have been described. It should also be mentioned that the usual content of niobium in terrestrial ores of industrial importance is usually 2–4%.
Proceeding from these results and taking into account the complex history of the formation and migration of sample 12013, one should turn to the studies of samples delivered to the Earth from the mainland regions of the Moon space probe “Luna-20” (February 1972) and “Apollo 16” spacecraft (April 1972). Some of these studies were undertaken repeatedly at a higher current level and yielded more accurate results.
Among the regolith samples from the sample delivered by “Luna-20,” anorthosite-type particles were isolated in which the sizes of metallic inclusions reached from tens to hundreds of microns. According to preliminary studies, the composition of this fraction falls into a typical meteorite region with a content of 5 to 7% nickel (Ni) and about 0.5% cobalt (Co) (Hubbard, Vinogradov, Ramendik, & Chupakin, 1977). At the same time, studies of anorthosite fragments revealed the presence of rare earth elements at a concentration 10 times greater than in typical meteorites of chondritic composition. When compared with the results of studies of the fine fraction of samples delivered by the “Apollo 16” spacecraft, it was found that in this case the concentration of rare earth elements in the sample of the “Luna-20” is two-thirds less. At the same time, the content of Co, Sc, Cr turned out to be higher by about one and a half to two times (Helmke, Blanchard, Larry, & Haskin, 1979). Similar results, reliably showing the presence of an asteroid substance on the Moon, were obtained by analyzing samples delivered to the Earth by the “Apollo 16” spacecraft. One example is the study of breccia sample 60035. The sample mass is 1.05 kg. The age of inclusion of anorthosite composition was determined as 4.09 ± 0.1 billion years. Analysis of this part of the sample revealed a high content of iridium (Ir), which, according to the authors of the study, indicates a reliable presence of inclusions of the asteroid substance (Ma & Schmitt, 1982).
A study of an anorthosite sample 60015, having a mass of 5.57 kg, also showed traces of a meteorite substance in the form of siderophiles with a relatively high content of iridium (Laul & Schmitt, 1973; Taylor et al., 1973). Similar results were obtained in the analysis of other samples of highland rocks from the “Apollo 16” collected during the expedition (Ebihara, Wolf, Warren, & Anders, 1992).
Real monitoring of shock events on the lunar surface, the possibility of which appeared in exploring the Moon with seismometers during the Apollo 12, Apollo 14, Apollon 15 and Apollo 16 space expeditions (NASA) shows that the inflow of a meteoric (asteroid) substance occurs constantly. On large-scale images obtained by the long-focus camera “LRO” (Lunar Reconnaissance Orbiter), new impact craters of various sizes are regularly found. As an example, we can compare the images obtained on December 2, 2012 (M183689789L) and July 27, 2013 (M1129645568L).
In Figure 8 the first image is placed on the left, the second image is shown on the right. In an image taken about eight months later, an impact crater with a diameter of 18 m appeared (Robinson, 2013). In the study by Speyerer, Povilaitis, Robinson, Thomas, and Wagner (2016), more than 14,000 such pairs of images were analyzed, resulting in 222 new craters with a diameter of 3 to 43 meters, formed over the previous seven years. Figure 9 shows the distribution of these objects. The red dots mark two shock events, which were also observed from the Earth.
When analyzing existing projects for the utilization of an asteroid substance in space, there are obvious prerequisites for using the option of searching for, developing, and delivering to the Earth appropriate material resources from the Moon. A number of aspects can be pointed out. As was shown, modern projects for the development of asteroids resources consider the development of objects of only small dimensions, no more than 10 meters across. On the lunar surface, the substance of asteroids of any size and mass that has fallen out during a historically long time can most likely be found. In the case of the development of asteroid resources of lunar origin, the technological side of space missions is greatly simplified, since such complex and energy-consuming stages as the search, capture, transportation, and placement of objects into special orbits are eliminated. It is also possible that economically this route will be more effective, since operations for the delivery of material from the Moon with the help of both automatic and manned systems have, in principle, already been worked out.
New studies of possible parameters of impact events are very important for solving the problem of using lunar resources of asteroid origin. As a result of modern simulation of asteroids’ incidence on the Moon, it was found out that at certain speeds the impactor does not evaporate during the high-temperature explosion as previously thought, but undergoes only mechanical destruction and its substance is largely retained inside the crater formed (Bland et al., 2008). According to these estimates, when the “slow” asteroids fall, 50% of the mass of the projectile is concentrated inside the formed crater, the rest of the fragmented material forms a nearby ejecta field.
Later, these provisions were confirmed and refined by a generalization of results based on 14,331 simulations of asteroid impacts (Yue et al., 2013). Figure 10 shows the histogram of the distribution of shock events from the impact velocities of the shock, based on the data obtained.
The shaded area of the graph corresponds to the selected group of “slow” asteroids, whose fall rate does not exceed 12 km/s. According to these results, the material of such percussionists is largely preserved on the lunar surface in a fragmented form inside the crater and in the surrounding ejecta field.
Statistical estimates have shown that about a quarter of all lunar craters of various sizes are formed as a result of the fall of “slow” impactors.
As an example of real education, which arose on all grounds as a result of the fall of the “slow” asteroid, we can cite a crater in the region of Mare Humorum, shown in Figure 11. The crater was identified in an image taken by the LROC NAC M157851844LE in May 2011 (Enns, 2011).
The next urgent task will be the development of a technique for the remote determination of lunar objects containing exogenous inclusions.
Preliminary studies in this direction were carried out based on the results of the lunar space missions “Chandrayaan-1” (India) and “SELENE/Kaguya” (Japan).
Studies using the M3 remote sensing system mounted on the “Chandrayaan-1” spacecraft discovered a new type of rock identified on the Moon, dominated by magnesium-enriched spinel (Pieters et al., 2011). The presence in the surface layer of spinels and olivines with a high magnesium content was also detected by the Spectral Profiler, installed on the “SELENE / Kaguya” spacecraft (Yamamoto et al., 2010). According to these results, it is possible to remotely identify the remnants of shock workers of different chemical composition inside the craters, where one can observe the presence of bottom sediments. Thus, the detection within the impact craters of such atypical minerals as magnesia-enriched spinels and olivines can serve as a reliable indication of the presence of an asteroid substance. Consequently, to the number of possible resources of the Moon, the authors of these studies rightly include nickel, cobalt, platinum, and rare metals of asteroid origin.
The modern remote sensing technique, using the registration of various physical radiations emanating from the lunar surface, taking into account the near-surface layers serving as sources of such flows, allows for a detailed study to identify local deposits of exogenous lunar resources.
The results of the researchers (Bland et al., 2008; Yue et al., 2013), served as the basis for the development of software products that, with a high degree of probability, allow us to determine the expected parameters of a shock event depending on the characteristics of the projectile.
Initially, software products were developed to simulate the impact of small bodies on the Earth. Then the same authors developed and implemented on the same basis a version of the simulator that works online, not only for the case of impactors falling on the Earth, but also on other solid planets (Collins, Melosh, & Marcus, 2005). The simulator was used to obtain the estimates given as follows (Marcus, Melosh, & Collins, 2017). As initial data, the drill size values, the expected angle of incidence, the velocity of incidence, the density of the impactor (ice, porous stone fragment, monolithic stone fragment, metal drummer), and the density of the surface substance of the object of incidence were introduced into the program. In the cases considered, the magnitude of the angle of incidence was assumed equal to 45°, as the most probable. The velocity of the fall was assumed equal to 10 km/s, as is most often encountered for “slow” asteroids according to Figure 10. The density of the surface substance for the Moon was considered to be, on average, 2.75 g/cm3 (density of the upper regolith layer).
The results of the calculations included the expected mass of the impactor, the values of the diameter and depth of the impact crater, the kinetic energy and impact energy, the state of the fallen body after the impact, and the probable frequency of such events in time.
Since the simulator (Marcus et al., 2017) allows calculations for impact events involving falling bodies larger than 100 m, a simulator (Hamilton, 2010) was used to analyze events with smaller impactors, allowing this to operate with any size of objects, up to microparticles.
Thus, the detection of fresh shock craters due to observations of the survey program LRO allows a comparatively accurate estimate of the real inflow of the asteroid substance to the lunar surface since 2012. As the analysis by the authors of the works (Speyerer et al., 2016; Yue et al., 2013) showed, in the aggregate of 222 craters, the largest number of objects in size group around the median value of 10 m. In addition, in Yue et al. (2013) it was shown that the fourth part of these shock events occurred as a result of the fall of “slow” asteroids, which had an average speed of 10 km/s.
The currently available definitions of the chemical composition of the asteroids approaching the Earth show that the objects most enriched with the metal fraction are S-type (stone) and M-type (metal) asteroids.
Simulations (Hamilton, 2010) show that a 10.1 m impact crater in the lunar surface layer is formed as a result of a 10 km/s drop of a stone asteroid measuring 0.8 m. The mass of an asteroid of this type was found to be equal to 803.8 kg. The impact crater of this diameter has a simple cup-like shape with a depth of 2 m. If we extrapolate the data obtained in Bland et al. (2008) regarding the impact velocity of the impactors at 10 km/s, the fraction of the asteroid substance preserved after the impact within the newly formed crater will be 22% of the mass of the falling body. With a typical ratio of the components in the S-type asteroids, the total mass of the metal fraction from the mass of the stone asteroid can be up to 40%, that is, 321.5 kg. Accordingly, the mass of the silicate phase is 482.3 kg. According to the calculated data, the composition of the metallic phase can be represented in the following form: iron—270.89 kg, nickel—48.23 kg, cobalt—2.41 kg, platinum and platinoids—0.012 kg.
To obtain a realistic estimate of the asteroid material influx to the lunar surface, it should be taken into account that the S-type asteroids in the population of bodies approaching the Earth make up 17%. Taking into account the isolation of “slow” asteroids from this population (25%), the final number of shock events involving “slow” S-type asteroids will be 9.4 events in seven years. However, estimates obtained in Hamilton (2010) suggest that one similar drop occurs every 25 days. The difference can arise because of the incomplete study of the distribution of lunar craters of similar dimensions. Consequently, the boundary values of the frequency estimation of the falls for the entire period under consideration are from nine to 102 events.
Thus, the substance of the metallic phase that arrived on the lunar surface as a result of the fall of the “slow” S-type asteroids about a meter in size can consist of the following masses: iron from 536.0 to 6079.2 kg, nickel from 95.4 to 1081.2 kg, cobalt from 4.9 to 51 kg, platinum and platinoids from 0.0234 to 0.2652 kg.
Similar calculations were made for the case of the fall of “slow” M-type asteroids. Calculations carried out according to the program (Hamilton, 2010) showed that the M-type falling bodies had a median size of 0.54 m, resulting in craters with a diameter of 10.1 m and a depth of 2 m. According to the same calculations, the frequency of the events considered is one drop every 25 days.
The total mass of the asteroid in this case is 660 kg and it has a completely metallic composition: iron—556.1 kg, nickel—99.1 kg, cobalt—4.9 kg, platinum and platinoids—0.025 kg. Since near-Earth metal asteroids average 10% of the total number of objects, the estimated number of falls in this period of time is 5.55 over seven years.
Thus, the estimation of the frequency of events involving M-type asteroids lies in the interval from about six to 102. The safety of the incoming matter in the impact crater is still estimated at 22%.
The final calculations give the following values of the mass of the asteroid substance preserved in impact craters of the considered origin in the form of bottom sediments: iron from 775.2 to 12503.4 kg, nickel from 138.0 to 2228.2 kg, cobalt from 6.6 to 110.2 kg, platinum and platinoids from 0.0342 to 0.5631 kg. Figure 12 provides a real example of how an impact crater that emerged as a result of the fall of a “slow” meteorite of the M-type can look. The image was taken from the orbit by the Narrow Angle Camera (NAC) LRO camera in the area of Lacus Autumni in the Orientale basin (M114498609) (Robinson, 2014).
According to calculations using a simulator (Hamilton, 2010), shown in Figure 12, the crater could be formed by a slow M-type asteroid measuring 28.5 m. The crater has a diameter of 600 m at a depth of about 100 m. The calculated value of the frequency of such events is one drop every 910 years. Particular attention should be paid to the nature of the field of ejecta and bottom sediments. With the probable mass of the projectile 107.56 tons, in crushed form, 23.7 tons of asteroid substance should remain on the lunar surface. A significant part of this fragmented material refers to the gland. But at the same time, in this case, probably 3.56 tons of nickel, 0.18 tons of cobalt, and up to 0.9 kg of platinum and platinoids.
To estimate the practically accessible volumes of the resources under consideration, it is necessary to involve data on the distribution on the lunar surface of craters of various sizes. The empirically obtained dependence of the density of the distribution of objects of different diameters per unit area has the general form of the power function: N = aDk, where N is the number of objects, in diameter of a large prescribed value of D by a constant area measure, a and k are constant parameters for individual regions of the Moon and certain intervals D (Shevchenko, 1980).
For example, for a typical sea surface and a crater population in the range from 10 m to 1000 m, the distribution can be represented by the following logarithmic dependence: log N = 11.36-2.68 D. Diameters of craters in this case are expressed in meters, and the area of reference is 106 km2. Using this dependence, taking into account all the limitations on the number of different types of impactors mentioned, it can be determined that there will be five 10-meter craters with 1 km impact of the substance from the S-type impactors and three craters with bottom sediments of M-type impactors. Consequently, the total amount of available asteroid matter per 1 km2 of the lunar surface can typically be: nickel—up to 12.1 tons, cobalt—up to 585 kg, platinum and platinoids—up to 3 kg.
However, it should be noted that this example demonstrates only the theoretical possibility of assessing the availability of asteroid-origin resources on the lunar surface. In the calculations, an insignificant mass of asteroid matter arrived at the Moon as a result of the precipitation of very small bodies for a limited period of time (seven years), covering only the actual observed shock events, was taken into account.
Using the simulator (Marcus et al., 2017), it can be established that an asteroid of M-type with a size of 1 km, when it falls at a speed of 10 km/s (a “slow” asteroid), forms a crater 20.25 km in diameter and 732 m deep. With the total mass of the projectile at 4.19 billion tons and provided that 22% of the mass of the fallen body remains in the impact crater, the total volume of the bottom sediments of the asteroid composition in this case can reach 921.8 million tons. According to the calculated proportions in the system (Lewis, 1997), this means that within the crater in the bottom sediments is likely to be 915.2 million tons of iron, 6.6 million tons of nickel, 0.33 million tons of cobalt, and 1,650 tons of platinum and platinoids.
Estimating the significance of the possible presence of such resources in the crater of the Moon alone, it is enough to recall that now annual production of platinum on the Earth (more precisely, annual supplies of platinum to the world market) has amounted to 170–180 tons (Matthey, 2016).
According to those working on the NASA–Keck project, which envisages the direct development of resources of a small (no more than 10 m size) asteroid, the cost of only the first stage—the capture and transportation of the object to the near-moon orbit—may amount to 2.6 billion dollars (Hecht, 2013). As mentioned, such expenses could be compensated in case of complete utilization of the M-type asteroid substance with a size of 10 m (Shaw, 2012). However, subsequent operations—the launch of a manned expedition, the actual development of the facility, and the delivery of the received material to Earth, will require additional costs.
If one turns to the sources of asteroid resources on the lunar surface, then the expected profitability of space missions is significantly higher. When considering only one case of a crater with a diameter of 20 km, as described, the market price in 2017 prices of the proposed bottom sediments of platinum and platinoids of 1,650 tons will amount to 51 billion dollars. The market value of the expected resources of nickel and cobalt in the same crater will be approximately $80 billion.
Calculations by the simulator (Marcus et al., 2017) give the frequency of the fall of an M-type asteroid the size of 1 km at a collision rate of 10 km/s as one event for every 456,601 years. If we take the period of intense meteorite-asteroid bombardment of the Moon as approximately equal to 3.8–3.9 billion years, according to the calculations of the event frequency, the total number of falls of “slow” asteroids of a given size and mass will be 8,536. As mentioned, only 10% of them, that is, ~ 854 events, can occur in the fall of metallic asteroids. Thus, the total mass of platinum and platinoids on the lunar surface as a result of the drop of only impactors with the described properties will amount to 14.1 million tons. It should be noted that this asteroid substance represents only a part of the possible bottom sediments in lunar craters, since our calculations did not take into account other types and sizes of impactors. But it should be remembered that modern estimates of possible volumes of asteroid resources on the Moon vary to different degrees depending on the initial data used, thus requiring additional studies of the lunar surface.
In this article, analytical studies of reputable world organizations confirming that the terrestrial reserves of rare and rare earth elements have been intensively depleted were presented. These trends, in turn, lead to the fact that the development of high technologies on Earth will begin to experience increasing difficulties. Therefore, the search for and disposal of extraterrestrial resources is pursued not so much for commercial purposes, but also as vital for the further progress of terrestrial civilization.
Historically, in the initial stage of studying the problems of utilizing space resources on a new level of knowledge and technology, the main attention of specialists was focused on projects for developing near-Earth asteroids. Despite the complexity of transport operations and severe restrictions on the size of bodies suitable for development, this direction was considered technologically feasible and quite cost-effective. With the advent of new research on the presence of an asteroid substance on the lunar surface, it became possible to consider other ways of solving such problems.
In mid-2016, it was announced that for the first time in NASA’s history of space exploration, the United States would issue an official permit to private company Moon Express Inc. to independently carry out a program of flights to the Moon to study and reclaim lunar natural resources (Pasztor, 2016).
As a long-term space program, experts still consider the creation of the lunar base. Since elements of space industrialization will inevitably become one of the directions of the extraterrestrial outpost of mankind, the issues of detection and utilization on the lunar surface of sediments of rare and rare earth elements of asteroid origin will become especially important.
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