Observational and Experimental Techniques

Characteristics of minerals in primitive chondrites, micrometeorites, and interplanetary dust particles (IDPs) such as chemical composition, crystal structures, textures, size, and shape indicate that solids and gases hardly reached equilibrium in the solar nebula. They may record a part of physicochemical conditions where dust formed or altered in the solar nebula or their parent bodies. Even the presence or absence of the minerals constrain the conditions in which they can survive or disappear. On the basis of the thermodynamical equilibrium models, which succeeded in predicting minerals stable in each temperature and pressure condition, laboratory experiments have played crucial roles in understanding kinetically controlled processes, such as evaporation, condensation (nucleation and growth), and chemical reactions, and deducing formation and alteration conditions in the solar nebula and their parent bodies from observations of primitive extraterrestrial materials. In laboratories, it is impossible to reproduce physicochemical conditions in the solar nebula mainly because of the limited laboratory timescales. Therefore, each experimental work focuses on a single process or reproduction of certain mineralogical characteristics observed in meteorites and IDPs. The kinetically controlled reactions of abundant minerals such as forsterite were examined by laboratory experiments of evaporation, gas–solid reaction, and condensation. Evaporation and condensation coefficients were determined based on the Hertz–Knudsen equation and nucleation theory, which are important parameters controlling timescales of reaction, temperature dependences, grain size or reaction volume, and chemical fractionation occurring in a limited timescale. In addition, chemical compositions and textures of amorphous metastable materials were systematically investigated by condensation experiments of nanoparticles. Various types of laboratory experiments and theoretical studies are complementary to each other for understanding the mineralogy of extraterrestrial materials and dust formation and evolution in the solar nebula.

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.