Meteoroid i meteoryt. Powrót do podstaw i definicji

The authors drew attention to the classification in December 2022 of over one ton of lunar meteorites that fell to Earth. They have been found since the early 1960s, but their first classification, as lunar meteorites, was made only in 1982. This was possible thanks to more advanced geochemical research and the possibility of comparing their results with the results of analyzes of samples of rocks and lunar regolith brought by the Soviet missions of the Luna program, and above all by several American missions of the Apollo program. With access to over 1.4 tons of lunar rocks on Earth, we are now able to conduct multidisciplinary studies of the lunar geology. Their results are particularly important in the context of building human settlements or lunar bases for further exploration of the solar system. This applies to both the physical properties of these rocks, as well as their chemical and mineral composition in the context of the presence of deposits of various mineral resources. It should be emphasized that meteoritic material from the Moon has been increasing in terrestrial collections (especially scientific ones) very quickly since 2015. This is the result of extensive exploration work, primarily in Antarctica, Africa, the Arabian Peninsula and Australia. Among the identified rocks reaching the Earth in the form of lunar meteorites, the most numerous are feldspar breccias (impact metamorphic rocks), anorthosites (plutonic igneous rocks building highlands areas of the silver globe) and basalts (extrusive igneous rocks building areas of the lunar maria). In addition, there are other igneous mafic rocks, such as gabbro, norite, troctolite and others. The surface of the crust is covered with regolith composed of fragments of the above-mentioned igneous rocks and breccias subjected to fragmentation by successive collisions with meteorites and micrometeorites and the action of solar wind particles (space weathering). As a result of these processes, the surface of the Moon is covered with a layer of loose sedimentary rock with a thickness of a few to several meters. Locally, a regolith may be a compact clastic sedimentary rock if a significant number of rock fragments are welded together with the glaze produced during collisions with micrometeorites. The authors also briefly presented the genesis and evolution as well as the geological structure of the Moon based on the results of the latest geophysical and geochemical (including isotopic) as well as mineralogical and petrological research. They pointed out that the proposed model of the genesis of the Moon from synestia formed after the collision of the proto-Earth with another hypothetical planetary embryo called Theia, explains well the chemical and isotopic homogeneity of the Earth and the Moon. The authors also pointed out that due to the common genesis, lunar meteorites are classified and named in the same way as terrestrial rocks, which definitely distinguishes them from other meteorites. The exceptions are Martian and HED meteorites, which are classified similarly to terrestrial rocks, although their names often do not have equivalents in the classification of terrestrial rocks (e.g. SNC meteorites). Tracking data on officially classified lunar meteorites, the authors found that in December 2022, the total mass of meteoritic matter considered to coming from the Moon exceeded 1 ton. Lunar meteorites are currently the largest source of information about the geology of the Silver Globe, accounting for almost two-thirds of the mass of lunar material available for study on Earth.